Progressive Crop Consultant May/June 2021

May / June 2021 

The Potential of Ultraviolet Light to Suppress 

Grapevine Powdery Mildew 

Developing a Nitrogen Fertilizer Plan for Olive Orchards 

Soil Health on Every Farm 

Transitioning from Hand to Machine Harvesting 

of Blueberries 

May/June 2021 

VINEYARD REVIEW 

Pages 37-51 

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Volume 6: Issue 3 

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4 

IN THIS ISSUE 

Transitioning from Hand 

to Machine Harvesting 

of Blueberries for Fresh 

Market 

PUBLISHER: Jason Scott 

Email: jason@jcsmarketinginc.com 

EDITOR: Marni Katz 

ASSOCIATE EDITOR: Cecilia Parsons 

Email: article@jcsmarketinginc.com 

PRODUCTION: design@jcsmarketinginc.com 

Phone: 559.352.4456 

Fax: 559.472.3113 

Web: www.progressivecrop.com 

CONTRIBUTING WRITERS & INDUSTRY SUPPORT 

12 

Developing a Nitrogen 

Fertilizer Plan for Olive 

Orchards 

Kris Beal 

Vineyard Team 

Robert Blundell 

Graduate Studen Researcher, 

UC Davis 

Akif Eskalen 

UCCE Specialist, Plant Pathologist, 

UC Davis 

Sonia Rios 

UCCE Subtropical Horticulture 

Farm Advisor, Riverside and San 

Diego Counties 

Steven Sargent 

University of Florida 

Fumiomi Takeda 

USDA-ARS 

16 

Pre-Plant Weed 

Management Followed 

by for Alfalfa Stand and 

Yield 

4 

Elizabeth J. Fichtner 

UCCE Farm Advisor, Kings and 

Tulare Counties 

David M. Gadoury 

Senior Research Associate, Plant 

Pathology and Plant-Microbe 

Biology Section, Cornell AgriTech, 

Geneva, NY 

Lisa Wasko DeVetter 

Washington State University 

Jeffrey Williamson 

University of Florida 

Eryn Wingate 

Agronomist, Tri-Tech Ag Products, 

Inc. 

22 

26 

Managing Soil and 

Structure Quality 

Avocado Invasive Insect 

Pests 

Mark S. Hoddle 

UCCE Specialist, Biological Control, 

UC Riverside 

Changying Li 

University of Georgia 

Sarah Light 

UCCE Agronomy Advisor, Sutter 

and Yuba Counties 

Craig Macmillan 

Niner Wine Estates 

Dr. Karl Wyant 

Vice President of Ag Science, 

Heliae Agriculture, Board of 

Directors, Western Region 

Certified Crop Adviser 

Wei Q. Yang 

Oregon State University 

32 


38 

46 


The Potential of Ultraviolet 

Light to Suppress 

Grapevine Powdery 

Mildew 

Irrigation Scheduling In 

Winegrape Vineyards 

16 

UC COOPERATIVE EXTENSION 

ADVISORY BOARD 

Surendra Dara 

UCCE Entomology and 

Biologicals Advisor, San Luis 

Obispo and Santa Barbara 

Counties 

Kevin Day 

UCCE Pomology Farm Advisor, 

Tulare and Kings Counties 

Elizabeth Fichtner 

UCCE Farm Advisor, 

Kings and Tulare Counties 

Katherine Jarvis-Shean 

UCCE Orchard Systems 

Advisor, Sacramento, Solano 

and Yolo Counties 

Steven Koike 

Tri-Cal Diagnostics 

Jhalendra Rijal 

UCCE Integrated Pest 

Management Advisor, 

Stanislaus County 

Kris Tollerup 

UCCE Integrated Pest Management 

Advisor, Fresno, CA 

Mohammad Yaghmour 

UCCE Area Orchard Systems 

Advisor, Kern County 

48 

Grapevine Trunk Diseases 

48 

The articles, research, industry updates, company profiles, and advertisements 

in this publication are the professional opinions of writers 

and advertisers. Progressive Crop Consultant does not assume any 

responsibility for the opinions given in the publication. 

May / June 2021 www.progressivecrop.com 3

TRANSITIONING FROM HAND TO MACHINE 

HARVESTING OF BLUEBERRIES FOR 

FRESH MARKET 

A look at machine harvesting in blueberries research from around the country. 

By FUMIOMI TAKEDA | USDA-ARS 

CHANGYING LI | University of Georgia 

LISA WASKO DEVETTER | Washington State University 

JEFFREY WILLIAMSON | University of Florida 

STEVEN SARGENT | University of Florida 

WEI Q. YANG | Oregon State University 

Blueberry production acreage in 

the U.S. is expanding. Across the 

country, commercial blueberry 

growers are increasingly using over-therow 

(OTR) mechanical harvesters (MH) 

to pick their blueberries for fresh market 

(Figure 1). Growers everywhere are experiencing 

difficulties in finding sufficient 

labor for hand harvest operations and 

due to the rising costs of labor. Harvesting 

blueberries with OTR harvesters can 

significantly reduce the overall cost of 

harvesting to a fraction of that needed for 

hand harvesting (HH) and workers needed 

for harvest operations from about 500 

hours of labor per acre per year to as little 

as three hours of labor per acre per year. 

However, compared to hand harvesting, 

OTR harvesting causes more berry loss 

due to falling on the ground and green/ 

red berries are harvested along with ripe, 

blue fruit. 

Detailed field testing of OTR harvesters 

for picking blueberries for the fresh market 

was conducted nearly 30 years ago in 

Michigan. That research in South Haven, 

Mich. evaluated the quality of blueberries 

harvested by hand and by four rotary 

and slapper harvesters that were used by 

growers at that time to harvest blueberries 

for processing. MH blueberries were 

sorted at the packinghouse (Figure 2). 

The most significant findings were a high 

percentage of detached blueberries had 

impact damage (Figure 3) and more 

than 20% of detached blueberries fell on 

the ground. The bruise damage was attributed 

to iImpact to the fruit created by 

the rapid actions of shaking rods and detached 

berries landing on the hard catching 

surface. Those studies revealed that 

blueberries harvested by the machines 

had a high percentage of blueberries with 

more than 20% of sliced surface area 

showing bruise damage (Figure 3 and 4, 

see page 5). Also, MH blueberries were 

much softer compared to hand harvested 

fruit. Their conclusion was that MH 

blueberries should not be cold-stored for 

more than two weeks while HH blueberries 

could go in controlled atmosphere 

storage for six weeks and air-shipped to 

Europe in excellent condition. 

Soon after, USDA engineers developed 

an experimental harvester called the V45 

harvester designed specifically to harvest 

fresh-market blueberries. It used a 

direct-drive shaker with an angled, double-spike-drum, 

a unique cane dividing 

and positioning system to push the canes 

out diagonally and cushioned catching 

Figure 1. A front view of Oxbo over-therow 

(OTR) blueberry harvester (all photos 

courtesy F. Takeda.) 

Figure 3. Bruise damage caused by mechanical 

harvesting makes the flesh dark and soft. Half of 

these berries have excessive bruising. 

Figure 2. Mechanical harvesting detaches 

unripe green fruit and clusters that 

must be sorted out on the grading line. 

4 Progressive Crop Consultant May / June 2021

Figure 4. Sliced examples of mechanically harvested blueberries. From left to right: 

Fruit with no internal bruise as indicated by no large discolored tissue; Fruit with 

impact damage at the stem end as indicated by discoloration inside the seed core; 

Fruit exhibiting damaged area from impact force to that triangular shaped, discolored 

section; and Discolored area has been highlighted in purple with SketchAndCalc 

program to calculate bruised area as 17% of the total cut surface area. 

surfaces to harvest fruit with minimum damage. With the V45 

harvester design, the detached blueberries dropped less than 15 

inches onto a soft neoprene sheet glued to a hard catch plate and 

soft sheet over the conveyor belt. 

These soft surfaces reduced impact force on the fruit detached 

by the V45 harvester. However, gluing a soft surface onto a hard 

surface has proven to show little reduction in bruise damage 

when harvesting is performed with conventional harvesters 

with two vertical drum shakers and berries falling more than 30 

inches. Only five V45 harvesters were sold by the now defunct 

B.E.I Inc. (South Haven, Mich.), although it was thought to have 

good fruit selectivity (low green fruit removal) compared to 

slapper models, little ground loss (fruiting cane pushed away 

from the crown) and superior quality over existing commercial 

harvesters at the time with two vertical drum shakers and either 

a metal or hard plastic catch surface. 

Sometimes, the fruit harvested by the V45 harvester had quality 

as good as commercially HH fruit. Its limitations were: 1) It 

needed to be driven much slower to avoid damaging bushes; 2) It 

could not harvest trellised rows or those with overhead sprinklers; 

and 3) It could not harvest all varieties, especially those 

with stiff, upright canes like ‘Jersey’ and many rabbiteye cultivars. 

The Fulcrum harvester made by A&B Packing Equipment 

(Lawrence, Mich.) has features like those of the V45 harvester. 

In the last ten years or so, U.S. blueberry farmers targeting the 

fresh market have been facing challenging economic situations 

(e.g., rising cost of hand picking, shrinking labor force, global 

competition, etc.) They and other specialty crop farmers have 

a greater interest in using automation and OTR machines to 

harvest their crop. The authors of this article have participated 

in different aspects of machine harvesting and sorting of 

blueberries to reduce the amount of internal bruise damage 

and in packing line sorting technology and damage detection 

systems to improve the quality of packed fruit. Several blueberry 

MH manufacturers (e.g., Oxbo International, Lynden, Wash.; 

A&B Packing Equipment, Lawrence, Mich.; BSK, Serbia; and 

FineFields, the Netherlands) have put more efforts devoted to 

developing MH systems that would impart low or no bruise 

damage so that fruits can be packed for fresh market. Following 

is a summary of recent developments in MH. 

Bruised Berries from Mechanical Harvesting 

Most OTR harvesters currently available are better suited for 

harvesting processed blueberries because they can cause 

excessive fruit damage. However, OTR machines have 

been used to pick blueberries for fresh market. In these 

instances, the fruit should be packed and transported to 

consumers as quickly as possible. When blueberries are 

HH, typically the picker gently picks ripe fruit selectively. 

In Chile and China, for example, ripe berries are picked 

individually to obtain high fresh quality. 

In the Pacific Northwest and elsewhere in North America, 

ripe fruit is often harvested by rubbing fruit cluster 

or sometimes by “tickling” them between the thumb 

and index finger and catching the detached berries in the palm 

and then placing them in a small harvesting bucket. In contrast, 

MH involves the shaking of the entire bush with rapid action of 

shaking rods to move canes back and forth. The cane movement 

causes ripe berries that need less fruit removal force than green/ 

red berries to be displaced from the fruit stem (pedicel) and 

fall onto catching surfaces. Experienced MH operators make 

slight adjustments on machine settings to obtain good selectivity 

(minimize green/red berry removal and maximize ripe fruit 

removal). 

The blueberry bush can range from 3 to about 6 feet tall with 

fruit located from the tip of the canes to branches near the 

ground, which causes the berries located on the top part of bush 

to fall as much as 50 inches. When an OTR harvester picks blueberries 

and fruit falls from that height onto plastic catch plates 

and conveyor belts, one can hear berries hitting the hard catch 

surfaces. 

Based on this simplified description of the blueberry MH process, 

it was apparent that the interaction between the machine 

and fruit should be better understood. To do this, we used a 

custom-made miniature electronic sphere called the BIRD 

(blueberry impact recording device developed at the University 

of Georgia) to measure the fruit impacts during MH process in 

2010 and 2011. The BIRD sensor for this study weighed 14 g. The 

later version, BIRD II, was built to closely approximate the size 

and weight of a large blueberry (9/16-in diameter and weighed 6 

g) (Figure 5, see page 6). 

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Peak acceleration(g) 

250 

200 

Day of bruise assessment 

Drop height (ft) Day of drop After 14 days 

150 

2 11.4 16.2 

3 100 14.4 19.7 

4 20.3 25.6 

2 50 3.1 4.9 

3 3.7 2.0 

0 0 6 12 18 24 30 36 42 48 

4 2.9 6.6 

0 0.6 2.0 

Drop height (inch) 

Continued from Page 5 

Along with documenting fruit impacts 

with a BIRD, a closeup video camera recorded 

the harvesting to pinpoint critical 

control points where most impacts were 

created. The results showed that the drop 

to the plastic catch plates on the harvester 

accounted for over 30% of all impacts 

on the BIRD, followed by the drop from 

the grading belt on the harvester into an 

empty lug (20%). When the lug is filled 

with blueberries, fruit-to-fruit impacts 

occur, which are much lower than when 

the fruit fall into an empty lug. 

Impacts created by the conveyor, including 

secondary bounce from the catch 

plates, and shaking rods combined for 

another 25% of recorded impacts. The 

remaining 25% of impacts that occurred 

before the sphere contacted the catch 

plate were classified as obscured impact 

events which could not be identified 

clearly from the video and were attributed 

to contact with the shaking rod, 

branches and the vertical tunnel panels. 

These measurements suggested that 

the most significant reduction in fruit 

impacts could be achieved by 1) Modifying 

the catch plates; 2) Reducing drop 

heights, either by restricting bush size, 

placing catching surfaces closer to the 

fruit or decreasing drop heights at other 

transition points; and 3) Placing softer 

surfaces at the transition points (e.g., 

at transfer points in the fruit handing 

equipment on the top of platform.) 

The two parts of the impacts include 

the number of encounters between the 

sphere and different surfaces of the 

harvester and the magnitude of these 

impacts. In our study, the harvesting 

process was documented with video that 

recorded time-stamped impact events 

with the larger, heavier BIRD I sensor. 

Legend 

Stainless steel plate 

Glued foam pad on 

stainless steel plate 

Suspended foam pad 

Suspended fabric net 

Figure 6. The relationship between various contact surface materials and drop height. The 

impacts were collected with a BIRD II sphere dropped from different heights. 

Using these parameters, the OTR MH 

process was divided into four phases: 

Phase I (detachment and falling), Phase 

II (fruit hitting the catch plate/conveyor 

belt), Phase III (elevation from the 

conveyor/transfer belt to the top platform 

and conveyance through a trash blower) 

and Phase IV (dropping from the conveyor 

belt into the lug). 

Results showed that for the rotary drum 

shaker, the BIRD sensor recorded an 

average of 18 impacts in Phases I to IV. 

During Phase I, it is assumed blueberries 

detached by fast-moving harvesting rods 

that shake left and right, impact branches 

as they fall and/or are flung out to the 

side panel. There were about five impact 

events in Phase I, but magnitudes of 

these impacts proved to be less significant 

than initially assumed. In Phase 

II, the BIRD contacted the catch plate 

and usually only one or two events were 

recorded. The magnitude of the impacts 

in Phase II was extremely high compared 

to impacts recorded in Phases I, III and 

IV. Our results strongly suggested that 

the high impact that the falling blueberries 

receive at the point of contact with 

the catch plate injures the fruit, resulting 

in fruit softening and larger bruise while 

the fruit is in storage (Figures 3 and 4, 

see page 5). 

Further analysis was performed by 

dropping the large, heavier BIRD I sensor 

onto a hard-plastic catch plate from 

different heights (6, 12, 24, 36 and 48 in) 

(Figure 6). As expected, the impact values 

(peak acceleration at impact (g) increased 

sharply linearly with increasing 

drop height, ranging from 280 g at 6 in 

to about 800 g at 48 in (data not shown). 

In subsequent studies, impact measurements 

were made using the smaller and 

lighter-weight BIRD II sphere by dropping 

onto soft surfaces created by placing 

Figure 5 . BIRD II (red sphere) connected 

with a 4-pin connector to a laptop to 

charge its internal battery, initiate impact 

measurements or download collected data 

to a laptop or mobile device. 

cushioned padding on top of the hard 

plastic plates or by suspending the soft 

material (no hard surface underneath.) 

A wide range of impact values were obtained 

depending on the hardness of the 

catch plate (Figure 6). Impacts greater 

than 200 g were recorded on hard surfaces 

such as a stainless-steel sheet and a 

plastic catch plate even when the BIRD II 

was dropped from a height less than 30 

cm (12 in). Gluing a soft surface to a hard 

surface reduced impact; however, this 

type of surface still created high impact 

above a one-foot drop height such that 

blueberries falling 30 inches onto such a 

surface would still be bruised. For example, 

the suspended foam sheet we used 

in our harvest-assist blueberry picking 

machine in 2017 generated less than 200 

g even when the drop height was 42 in, 

but well above the 120 g at which ripe 

blueberries can be bruised by impact 

force. Only the netted fabric that acted 

like a hammock produced low enough 

impact force and kept the blueberries 

from getting bruised even when the fruit 

was dropped from a 48-in height. Thus, 

it was thought that replacing the hard, 

plastic fruit catching and collection surfaces 

with soft and durable catching surface 

materials and plate design features 

that prevent soft surface from contacting 

any hard surfaces underneath had the 

potential to improve the quality of MH 

blueberries and reduce bruise damage 

associated with high mechanical impact. 

In terms of mechanical impact to blueberry 

fruit, our research has shown that 

bruise damage and the loss of firmness 

in MH fruit can be decreased by reducing 

space between blueberries on 

the bush and the catching surface to 12 



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inches in the case of hard plastic fruit 

catching surfaces or by modifying the 

fruit catching surfaces to create a softer 

fruit landing surface. Ideally, the fruit 

catching surface should not exceed 

120 g impact even when the BIRD II is 

dropped from a height of 48 in (equivalent 

to the distance between the top of a 

large mature blueberry bush and catch 

plates on the harvester). 

The design of soft surfaces can be 

achieved by either incorporating netted 

material or a soft “rubber” sheet with no 

hard surfaces beneath for catching the 

fruit (Takeda and Wolford, U.S. Patent 

No. 9,750,188 and the Oxbo SoftSurface 

kit). For example, even with a soft 

surface insert in a hollowed-out plexiglass 

catch plate, the margins of the plate 

contributed to more than 20% of the 

exposed surface area. In addition, catch 

plates on the harvester overlapped with 

adjacent plates and rested on top of another 

plate. The outline of the plate below 

another created about 10% additional 

hard surfaces. 

When blueberries are HH, the packout 

is about 95% or better and fruit usually 

have little or no internal bruise damage 

(Table 1). The packout of MH blueberries 

is lower and typically ranges from 70% to 

slightly more than 80%. The remaining 

20% consists of soft, overripe and immature 

green- and red-colored berries. 

Commercial packing operations, for 

the most part, do not check for internal 

bruise damage in their MH blueberries. 

However, close inspections of MH 

blueberries packed into clamshells after 

sorting on commercial packing lines 

revealed berries were bruised (Figure 3, 

see page 4). Our studies evaluated different 

catch surface designs by inserting 

soft, flexible material to reduce internal 

bruise damage. We did record improvements 

in packout. However, neither 

the improvement in packout nor berry 

firmness approached that of HH fruit 

in the case of varieties Duke, Draper 

or southern highbush blueberry (SHB) 

Optimus even when they were harvested 

with OTR machines equipped with soft, 

flexible catch surfaces. The only exception 

to date has been the variety Last 

Day of bruise assessment 

Surface Drop height (ft) Day of drop After 14 days 

2 11 .4 1 6.2 

Hard 

3 14.4 1 9.7 

4 20.3 25.6 

2 3.1 4.9 

Soft 

3 3.7 2.0 

4 2.9 6.6 

Not dropped 0 0.6 2.0 

Table 1. Effect of catch surface (hard or soft) and drop height on internal bruise damage 

within one day of drop and after 14 days in cold storage (32 degrees F to 37 degrees F). 

Bruise damage is expressed as the percentage of cut surface area indicated by dark color 

(see Figure 4, see page 5). 

Call, where MH produced the quality 

approaching that of HH berries. MH of 

SHB Optimus produced higher-quality 

packout than other SHB varieties, such 

as Jewel, Star and Farthing, but even 

Optimus should not be cold-stored for 

more than one week. Our studies have 

shown that fresh market pack-out can 

be increased by installing a soft catch 

surface on the harvester, but the quality 

of HH blueberries has been better. 

Cultivar Susceptibility 

In a study conducted in Oregon, the 

susceptibility of 11 blueberry cultivars 

to impact damage was determined by 

dropping the fruit from 2-, 3-, and 4-foot 

heights onto a hard, plastic catch plate. 

Bruises developed more rapidly in rabbiteye 

cultivars (Ochlocknee, Powderblue 

and Overtime) than in northern highbush 

(NHB) and SHB cultivars. NHB 

cultivars Aurora, Cargo, Draper and Last 

Call had the least amount of bruising 

after two weeks in cold storage. Blue Ribbon, 

Legacy and Liberty had a moderate 

amount of bruising. 

These studies showed that simulated 

drop tests are useful in determining the 

potential of varieties for long-term cold 

storage and, more importantly, their 

potential to MH for fresh market. In a 

study in 2020 in Oregon, Draper and 

Legacy were MH with two OTR Oxbo 

harvesters, one fitted with and the other 

without the SOFTSurface kit. To date, 

the challenge for Oxbo Corporation and 

other machine manufacturers has been 

to procure soft materials that meet food 

safety standards and are durable for 

harvesting blueberries. 

The preliminary findings of this study 

were: 1) Machine harvesting with the 

SOFTSurface kit reduced fruit internal 

bruise damage in both Draper and Legacy 

fruits compared to those harvested 

with the unmodified OTR harvester as 

shown with a laboratory test (Table 1); 2) 

Draper and Legacy fruit harvested with 

the machine fitted with the SOFTSurface 

kit and sampled before sorting in the 

packing house were firmer compared 

to fruit harvested by the unmodified 

harvester; and 3) After one and two 

weeks in cold storage, there was no difference 

in firmness of berries harvested 

by machines fitted with and without the 

SOFTSurface kit. 

We found that fruit firmness-based sorting 

by itself may not be a good predictor 

of berry quality when MH blueberries 

are cold-stored for two weeks or more, 

but both Draper and Legacy blueberries 

picked by the OTR machine fitted with 

the SOFTSurface kit maintained better 

fruit firmness (>160 g/mm) values and 

lower internal bruise ratings in cold 

storage (Table 1). The improvements in 

fruit quality may well have been from a 

70% reduction in hard catch surface area 

in the SOFTSurface kit compared to the 

hard polycarbonate fruit catching surfaces 

in the regular harvesters. A laboratory 

test determined the effects of dropping 

blueberries from different heights onto 

either a hard (e.g., polycarbonate catch 

plate on conventional harvesters) or soft 

catch surface (e.g., prototype SOFTSurface 

kit) on internal bruise development 

(Table 1). Blueberries were sliced to 

visually assess bruise damage on the day 

of the drop test and after cold storage for 

two weeks. 

Young (~3-ft-tall) and mature (6-ft-tall) 

trellised Last Call blueberry plants were 

either HH or picked with a modified 

OTR machine. Fruit samples from both 

methods were manually sorted and 

evaluated for internal bruise damage 

on the day of harvest and the remaining 

samples were placed in cold storage. 

Cold-stored samples were taken out after 


two and four weeks and evaluated for internal bruise damage 

(Table 2). On the day of harvest (zero days after harvest), about 

80% of blueberries showed no bruise damage, and the remainder 

showed damage ranging from 1% to more than 50%. There 

was little change in internal bruise for samples from matures 

bushes that were either HH or MH. However, there was a 

dramatic decline in the percentage of fruit with no internal 

damage among the samples from machine harvesting of young 

plants. 

Our field observations of the Last Call bushes used in this 

study indicated that the canes of young plants were upright 

during the harvest and detached fruit fell straight down. In 

contrast, on the taller, mature bushes, the canes had grown 

well above the height of the trellis and they were leaning 

outward at the time of harvest. This placed the fruit away from 

the crown and less than 30 inches above the catching surface 

and may have contributed to reducing mechanical impacts in 

terms of numbers and magnitude, thus reducing the amount of 

internal bruise damage. 

Sorting Out Bruised Berries 

Blueberry growers in the Pacific Northwest and in Chile have 

expressed an interest in machine harvesting blueberries for the 

export market. The consensus among them is that the varieties 

for the export market must be firm and arrive at the destination 

in excellent condition after more than three weeks of cold 

storage and a transoceanic travel period. Our machine harvesting 

research has consistently shown that the MH blueberries 

generally had more internal bruise damage and shorter shelf 

life than the HH blueberries. 

Commercial optical sorting equipment are now available 

for grading blueberries. In the last three years, HH and MH 

blueberries have been processed on commercial blueberry 

packing lines in Oregon and Washington equipped with an 

optical sorter (e.g., UNITEC, BBC and MAF). For each packing 

line, samples of Draper and Legacy were taken from lugs prior 

to unloading onto the conveyor system, and a second group 

of samples were collected after the fruit had gone through the 

optical sorting machine. Samples from both locations were assessed 

for bruise damage (% bruised area). The bruise data are 

presented in Table 3 in which the data are expressed in terms 

of how the samples were distributed (e.g., blueberries with no 

damage to those that were severely bruised.) The analysis indicated 

that sorting by optical sorters did not remove blueberries 

with moderate to severe internal bruise damage. 

Next, we compared the blueberry fruit firmness value with the 

area of internal bruise damage on the sliced surface. One would 

likely assume that softer fruit will have more bruise damage. 

Our results and those from a report by Chilean researchers 

showed that this was not the case as shown by the low correlation 

coefficient (r-value) for these two fruit quality parameters. 

Whether the fruit had been collected from the packing line 

before or after the optical sorting machine, the correlation 

coefficients for berry firmness and bruise damage were less 

than 0.4 in NHB cultivars. This suggested that optical sorters 

in commercial blueberry packing houses were not effective in 

removing blueberries with internal bruise damage. 

Once more in the laboratory, we conducted drop tests in which 

HH Duke blueberries were dropped from a height of 62 inches 

to ensure that the samples would be bruised. A hyperspectral 

imaging system was used to locate and quantify bruise damage 

in each whole fruit (25 berries at a time). We then measured 

fruit firmness with a FirmTech II at the site of the bruise impact 

as determined by the imaging system. Then, the same fruit was 

rotated and additional firmness measurements were taken at 90 

and 180 degrees from the bruised site. 

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0 1 2 3 4 5 

Harvest method** Bush age At harvest y 

OTR machine Young 7 8 5 8 9 1 0 

OTR machine Old 89 0 3 3 4 2 

Hand Old 7 8 1 6 1 0 5 1 

After 1 4 days in cold storage 

OTR machine Young 47 3 9 9 1 3 21 

OTR machine Old 7 7 2 6 6 6 4 

Hand Old 80 2 1 0 3 5 2 

After 28 days in cold storage 

OTR machine Young 43 2 8 15 16 16 

OTR machine Old 86 1 3 6 2 3 

Hand Old 86 1 3 6 2 

*The IBD categories are on a scale of 0 to 5, with 0 representing 0% IBD, 1 representing 1 % to 5% IBD, 2 

representing 6% to 1 0%, 3 representing 1 1 % to 20%IBD, 4 representing 21 % to 50% IBD and 5 

representing more than 51 % IBD. 

**Fruit samples were randomly collected on the day of harvest. 

Table 2. Percent of blueberries in each internal bruise damage (IBD) category 

as affected by hand harvesting and harvesting with a modified OTR 

machine and the age of ‘Last Call’ northern highbush blueberry immediately 

after harvesting and after two and four weeks in cold storage. 


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Internal bruise damage (% of samples in each category) 

Cultivar Location 0 1 2 3 4 5 

Draper Before 33.5 1 .5 21 .5 30.0 1 1 .0 2.5 

After 22.5 7.5 26.5 30.0 1 1 .0 2.5 

Legacy Before 47.0 1 .0 21 .5 20.5 1 3.0 2.0 

After 23.5 1 .0 1 7.5 30.0 1 8.5 9.5 

Table 3. Determination of internal bruise damage in machine-harvested Draper and Legacy 

blueberry samples collected from packing line locations either before or after inspection 

with an optical sorter. Samples were sliced through their equator and the bruised area was 

assessed visually as the percentage of sliced area and converted to a value between 0 and 5 

using a 5rating scale: 0= no bruise, 1= 1% to 5% bruised, 2= 6% to 10%, 3= 11% to 20%, 4=21% 

to 50% and 5= greater than 50%. 


The analysis showed that at the site of 

the bruise damage, the average fruit 

firmness was 149 g/mm. However, at the 

sites that were 90 and 180 degrees from 

the impacted location, the firmness was 

greater than 162 g/mm. This meant that 

a lower firmness value was detected 

when the damaged area was purposely 

used to determine firmness, resulting 

in a much higher r-value between fruit 

firmness and internal bruise damage 

values. Fruit that were firm at the time 

of packing (e.g., >180 g/mm value using 

a FirmTech II instrument) were found to 

have internal bruise damage exceeding 

15%. In the near future, our research 

team will sort MH blueberries with 

this imaging system to separate whole 

unbruised and bruised blueberries and 

conduct postharvest quality evaluation 

for unbruised and bruised MH blueberries 

to determine the shelf life of each 

group with an eye toward exporting MH 

blueberries to distant Asian markets. Of 

course, taking this non-destructive imaging 

system from the laboratory bench 

to integrating it into commercial optical 

sorting machines for IBD detection and 

sorting is a challenge facing the machine 

manufacturers. 

Conclusions 

More blueberries for fresh market are 

being machine harvested. 

Machine harvested blueberries have 

more internal bruise damage. 

On-going research is developing a better 

understanding of what causes bruising 

and working with harvest machine manufacturer 

to reduce bruise damage. 

New sensor technologies for blueberry 

sorting could assist in reducing bruised 

berries in fresh packs. 

Our research has shown that to make 

MH more profitable for blueberry growers, 

the current OTR harvesters must 

be modified to reduce impact damage 

and ground loss. Cultivars with superior 

machine harvestability are being 

released by blueberry breeding programs, 

and research must continue to develop 

equipment capable of harvesting blueberries 

with less bruise damage. The sorting 

system on the packing line for MH 

fruit must be improved with a greater 

precision to eliminate fruit with severe 

internal bruise damage. This would ensure 

that the quality of MH blueberries 

going into clamshells would be as good 

as HH fruit. Blueberry growers in some 

regions can then contemplate having 

MH blueberries packed for export. Also, 

proper training and pruning of blueberry 

bushes to maintain a small crown can 

increase MH efficiency. These changes 

will help in making small, incremental 

improvements in increasing pack-outs 

and fresh quality of packed blueberries. 

Finally, in order for MH blueberries to 

have quality that is as good as HH fruit, 

the blueberry industry needs to be willing 

to make changes by growing superior 

varieties, modifying how blueberry bushes 

are grown and harvested, and improving 

how the fruit is sorted. This will take 

a concerted effort from growers, breeders, 

horticulturists, engineers and supply 

chain specialists. These changes could 

lead to blueberry fields that look different 

from what we see today, with radically 

different ways of harvesting blueberries 

and technological advancements for sorting 

blueberries with the goal of improving 

the quality of MH blueberries going 

into clamshells. 

In terms of harvesting and packing technology, 

it is envisioned that U.S. blueberry 

growers will be using robotic harvesting 

systems in the field or in warehouses 

with specialized automated or semi-automated 

harvesting machines that will 

avoid damaging berries, have better 

selectivity to reduce green berries picked 

and sort out over-ripe and diseased 

berries in the field. In packing houses, 

new non-destructive technologies are 

needed that will be capable of analyzing 

the blueberry fruit surface and below the 

skin and sort fruit for quality (large size, 

high sweetness, flavor, bloom, no bruise 

damage and color). These advances will 

facilitate market segmentation and high 

prices as one U.S. and several European 

blueberry distributors are doing already 

with HH blueberries. 

This research was supported in part by 

the U.S. Department of Agriculture 

agencies (Agricultural Research Service 

(Project No. 8080-21000-028, National 

Institute for Food and Agriculture 

(Agreement No. : 2008-51180-19579 and 

2014-51181-22471), Agricultural Marketing 

Service (FY 18 Oregon Department 

of Agriculture SCBG to WQY and 

FY18 Washington SCBG to LWD), U.S. 

Highbush Blueberry Council, Chilean 

Blueberry Committee and Naturipe 

Farms Blue Challenge. 

Our gratitude goes to blueberry growers 

and packers in Waldo, Fla.; Alma 

and Homerville, Ga.; South Haven and 

Grand Junction, Mich.; Kingsburg and 

Stockton, Calif.; Hillsboro, Independence 

and Roseburg, Ore.; and Burlington, 

Prosser, Lynden and Sumas, Wash., 

and in Chile who provided much needed 

in-kind support to the harvest project. A 

special thanks goes to Oxbo International 

Corporation which has collaborated 

with the group since 2014. 

Authors are employees of USDA-ARS (FT, 

fumi.takeda@usda.gov) Oregon State 

University (WQY, wei.yang@oregonstate. 

edu), University of Georgia (CL, cyli@uga. 

edu), Washington State University (LWV, 

lisa.devetter@wsu.edu) and University of 

Florida (SS, sasa@ufl.edu and JW, jgrw@ 

ufl.edu). 

Mention of trade names or commercial products 

in this publication is solely for the purpose 

of providing specific information and does not 

imply recommendation or endorsement by 

the U.S. Department of Agriculture. USDA is an 

equal opportunity provider and employer. 

Comments about this article? We want 

to hear from you. Feel free to email us at 

article@jcsmarketinginc.com 


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Developing a Nitrogen 

Fertilizer Plan for Olive 

Orchards 

By ELIZABETH J. FICHTNER | UCCE Farm Advisor, Kings and Tulare Counties 

Plant tissues pruned from the trees are typically flail mowed for reincorporation into the orchard floor. Nitrogen 

incorporated in this biomass will be released by mineralization (courtesy E. Fichtner.) 

Nitrogen management plans 

(NMP) for California olive 

orchards are essential for the Irrigated 

Lands Regulatory Program and 

can increase net return. A good NMP 

has the potential to increase yield, improve 

oil quality and mitigate biotic and 

abiotic stresses while reducing nitrogen 

losses from the orchard. 

Olives differ from other orchard crops 

in California in that they are both evergreen 

and alternate bearing. Individual 

leaves may persist on the tree for two to 

three years. Leaf abscission is somewhat 

seasonal, with most leaf drop occurring 

in late spring. 

Rapid shoot expansion occurs on 

non-bearing branches during the hottest 

part of the summer (July/August) 

on ‘Manzanillo’ olives in California. 

The fruit on bearing branches limits 

current-season vegetative growth. 

Olives bear fruit on the prior year’s 

growth, and the alternate bearing cycle 

is characterized by extensive vegetative 

growth in one year followed by 

reproductive growth the following year 

(Figure 1). With bloom occurring in 

late April to mid-May, fruit set can be 

estimated in early July, allowing for 

consideration of crop load while interpreting 

foliar nutritional analysis in late 

July-early August. 

Critical Nitrogen Values 

Foliar nitrogen content in July/August 

should range from approximately 1.3% 

to 1.7% to maintain adequate plant 

health. The symptoms of nitrogen 

deficiency manifest when foliar nitrogen 

content drops to 1.1% N. As leaves 

become increasingly nitrogen deficient, 

foliar chlorosis progresses from yellow-green 

to yellow. Leaf abscission is 

common at nitrogen levels below 0.9%. 

Nitro- 

gen deficiency in olive is associated 

with a reduced number of flowers per 

inflorescence, low fruit set and reduced 

yield. 

Table 1. The quantity of nitrogen removed per ton of fruit at harvest 

varies by variety. 

Variety 

1 ton per acre 

crop 

(lbs. Nitrogen) 

Arbequina 6.81 

Arbosana 

Koroneiki 

Manzanillo 

6.39 

7.45 

8.04 


crop 


34.07 

31.97 

37.26 

40.22 

Year 1: Spring ON bloom 

Year 1 - Summer ON crop 

Year 2 - Spring OFF bloom 

Year 2 - Summer OFF crop 


crop 


68.14 

63.94 

74.51 

80.44 

Source: Total Fruit Nutrient Removal Calculator for Olive in California B. Krueger (UCCE Glenn County) 

and R. Rosecrance (California State University, Chico). 

Year 3 - Spring ON bloom 

Figure 1. Illustrative model of the alternate bearing cycle of olive (courtesy 

Carol Lovatt, UC Riverside.) 


Excess nitrogen (>1.7%) adversely affects oil quality. Oil with 

low polyphenol concentration is associated with orchards 

exhibiting excess nitrogen fertility. Since polyphenols are 

the main antioxidant in olive oil, reduced polyphenol levels 

are associated with reduced oxidative stability. 

Nitrogen content may impact orchard susceptibility to biotic 

and abiotic stresses. For example, while excess nitrogen 

content has been associated with increased tolerance to 

frost prior to dormancy, it is associated with sensitivity to 

low temperatures in spring (post-dormancy). High nitrogen 

content has also been associated with increased susceptibility 

to peacock spot, a foliar fungal disease on olive. 

Foliar Sampling for Nitrogen Analysis 

By convention, foliar nutrient analysis is conducted in late 

July to early August in California. Fully-expanded leaves 

are collected from the middle to basal region of the current 

year’s growth at a height of about five to eight feet from 

the ground. To capture a general estimate of the nitrogen 

status of the orchard, samples should be taken from 15 to 30 

trees, with approximately five to eight leaf samples collected 

per tree. Leaves for analysis should only be collected from 

non-bearing branches. Growers may find it beneficial to 

make note of the ‘ON’ and ‘OFF’ status in the historical 

records of each block. The orchard bearing status, combined 

with anticipated yield and foliar analysis, will guide decisions 

for nitrogen applications the following 

year. 

Figure 2. Approximate distribution of nitrogen in the aboveground 

portion of olive trees. 

33% 19% 

44% 

4% 

Leaves 

Twigs/Branches/Trunk 

Fruit (pulp) 

Fruit (pit) 

Adapted from: Rodrigues et al. 2012 

Figure 2. Approximate distribution of nitrogen in the aboveground portion of 

olive trees (source: Rodrigues et al. 2012.) 

Estimation of Nitrogen 

Removed from the Orchard 

The easiest component of orchard nitrogen 

loss to estimate is the N in the harvested 

fruit. A ton of harvested olives removes 

approximately 6-8 lbs N from the orchard. 

The quantity of nitrogen in the fruit varies 

slightly between olive varieties (Table 1, 

see page 12). Growers can use the Fruit 

Removal Nutrient Calculator for Olive on 

the CSU Chico website to gain estimates of 

N removal by the three oil varieties (Arbequina, 

Arbosana and Koroneiki) and the 

Manzanillo table olive. This tool was developed 

by Dr. Richard Rosecrance, a professor 

at CSU Chico, and Bill Krueger UCCE farm advisor. To 

access the Fruit Removal Nutrient Calculator for Olive, visit 

rrosecrance.yourweb.csuchico.edu/Model/OliveCalculator/ 

OliveCalculator.html. 

Pruning may generate a second component of nitrogen loss 


Nitrogen Distribution in the Tree 

Over 75% of the aboveground nitrogen in 

the olive tree is incorporated in the vegetative 

biomass (Figure 2). The twigs, secondary 

branches, main branches and trunk 

account for approximately 33% of aboveground 

nitrogen. 23% of the aboveground 

nitrogen is harbored in the fruit, with the 

majority in the pulp (19%). Fruit is only an 

important nitrogen sink during the initial 

phase of growth. As fruit size increases, the 

N concentration decreases due to dilution. 

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from orchards. The best practice to mitigate 

nitrogen loss from pruning is to 

reincorporate the pruned material into 

the orchard floor by flail mowing. The 

nitrogen in this organic material will 

gradually become available to the trees 

through mineralization. 

In mature orchards, the wood removed 

by annually pruning is approximately 

equal to the annual vegetative growth. 

Consequently, the input and removal of 

nitrogen in vegetative growth is cyclic 

and almost equal in mature orchards. 

In young orchards, nitrogen inputs are 

utilized to support vegetative growth 

and little N is removed from the 

orchard in prunings or crop. During 

this time, nitrogen must be supplied to 

meet the demand to support vegetative 

growth. It is estimated that approximately 

2.5 lbs N is required to produce 

1000 lbs fresh weight of tree growth. 

Nitrogen Use Efficiency 

Not all the nitrogen supplied to the orchard 

from fertilizer and other inputs 

(i.e., organic matter, irrigation water) is 

utilized for tree growth and crop production. 

A fraction of nitrogen is lost 

from the orchard ecosystem through 

processes such as runoff, leaching and 

denitrification. Efficiency varies among 

orchards, with some orchard systems 

exhibiting higher nitrogen utilization 

rates than others. The efficiency generally 

varies from 60% to 90%. Higher 

values denote more efficient use of nitrogen 

inputs. To estimate the amount 

of nitrogen to supply an orchard, the 

demand is divided by the estimated 

efficiency. For example, if nitrogen demand 

is 50 lbs. per acre and efficiency 

is estimated at 0.8, then 62.5 lbs N per 

acre should be applied. 

Nitrogen management plans are 

site-specific and designed to meet orchard 

and crop demand while reducing 

environmental losses. Nitrogen utilization 

is never 100% efficient. Nitrogen 

use efficiency can be maximized by 

minimizing losses from irrigation and 

fertilization practices while utilizing foliar 

analysis and knowledge of alternate 

bearing status to fine-tune applications. 

References 

Fernández-Escobar, et al. 2011. Scientia Horticulturae 

127:452–454. 

Hartman, H.T. 1958. Cal Ag. Pgs 6-10. 

Rodrigues, M.A. et al. 2012. Scientia Horticulturae 

142:205-211. 




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PRE-PLANT WEED MANAGEMENT FOLLOWED BY IN-SEASON 

CONTROL FOR IMPROVED ALFALFA STAND AND YIELD 

By SARAH LIGHT | UCCE Agronomy Advisor, Sutter and Yuba Counties 

Good stand establishment is 

critical for productivity of an 

alfalfa field both in year one 

and in subsequent years. Weed competition 

during stand establishment 

may be irreversible because it can 

reduce alfalfa root growth and lead 

to thinner alfalfa stands and lower 

forage quality. Thus, it is important to 

have good weed control during alfalfa 

stand establishment. 

This project evaluated the efficacy of 

weed control options for both conventional 

and organic growers. Pre-plant 

mechanical cultivation and glyphosate 

spray were evaluated with the 

goal of providing regionally relevant 

information about an integrated weed 

management tool for improved stand 

establishment. 

Methods 

Six treatments (Table 1) were replicated 

three times in the field. Main plots 

were a pre-plant treatment (either no 

pre-plant treatment, pre-plant tillage 

or pre-plant glyphosate). Additionally, 

half of the plots received later in-season 

treatment (Table 1): either no treatment 

or Raptor application in-season after 

the crop had emerged. 

This field was planted in the spring in 

the Sacramento Valley of California. 

Weeds were germinated with winter 

rains. On some plots (treatments 3 and 

6), pre-plant glyphosate was sprayed 

on plots on January 31, 2020 at a rate of 

three pints glyphosate/acre. On other 

plots (treatments 2 and 5), mechanical 

cultivation was implemented on 

February 11, 2020 once the soil was 

dry enough. This cultivation was very 

shallow (top few inches of the soil) to 

avoid bringing new weed seeds to the 

soil surface. 

Alfalfa seed was flown on the field on 

March 4, 2020, and the field was then 

EXPERIMENTAL TREATMENTS 

T RE A TMENT N UM BER PRE -PLA NT TREA TMEN T IN -S E A S O N TRE ATMEN T HERBICIDE R A TE (S ) 

1 N o n e N o n e N / A 

2 T illa g e N o n e N / A 

3 G ly p h o s a te N o n e 3 p t / a c r e 

4 N o n e R a p to r 6 fl o z / a c r e 

5 T illa g e R a p to r 6 fl o z / a c r e 

6 G ly p h o s a te R a p to r 3 p t / a c r e + 6 fl o z / a c r e 

Table 1. Six treatments were replicated three times in the field. 

ring-rolled to cover seed and get good 

seed-to-soil contact. The field was then 

irrigated for germination a week later. 

In-season weeds were controlled on 

some of the plots (treatments 4, 5 and 

6) with a tank mix of Raptor (Imazamox 

Ammonium Salt) at 6 fl oz per 

acre and Buctril (Bromoxnil) on April 

25, 2020. 

Data Collected 

Baseline weed counts were taken on 

January 29, 2020 from all plots before 

treatment implementation but after 

weed germination. Individual broadleaf 

weeds and grasses + sedges were counted 

in three random 20x20 cm quadrats 

per plot. Plants were counted on this 

date because weeds and alfalfa plants 

were small and percent cover would not 

have captured potential differences. 

Weed counts were taken an additional 

three times between planting and first 

cutting from all plots. In-season weed 

counts were taken as percent cover 

in which the area of the quadrat was 

broken up in percent covered with 

broadleaves, grasses + sedges, bare soil 

and alfalfa. On April 9 and May 14, 

2020, weed counts were taken in three 

random 20x20 cm quadrats per plot, 

and on June 8, 2020, percent cover was 

observed in three random square-meter 

quadrats per plot. The larger quadrat 

was used for percent cover on June 8 

because alfalfa and weeds were tall 

at this time and the meter by meter 

square allowed for more accurate representation 

of each plot. 

Plots were hand harvested on June 8, 

2020 prior to first cutting by the grower, 

which occurred on June 10. Two 

square-meter areas of each plot, which 

were representative of the larger plot, 

were cut. Yield biomass was separated 

into weeds and alfalfa, dried, weighed 

separately and then converted to a 

pounds dry matter/acre basis. 

Finally, on June 23, 2020, following first 

cutting, alfalfa stand counts were taken 

in all plots by counting the number 

of alfalfa plants in three 20x20 cm 

quadrats. 

Baseline and Early Weed Counts 

The first weed counts (January 29, 2020) 

collected before treatment implementation 

showed the average count for 

grasses + sedges for all plots was zero at 

this count. For broadleaves, there were 

no significant differences by treatment, 

but there were significantly more weeds 

in the side of the field with no in-season 

control compared to the side where 

Raptor was applied in-season. 

April 9, 2020 Weed Counts 

Grasses + sedges: There were not many 

grasses or sedges in the field. 

Broadleaves: There were significantly 

less broadleaves in the plots that had 

pre-plant weed control (glyphosate or 

tillage). 

Alfalfa: Alfalfa plants were small at this 

counting date; however, there were 

significant treatment differences with 



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Percent Broadleaf Weeds 

Percent Alfalfa Plants 

Yield (lb/A in 100% dry weight 

100 

75 

50 

25 

0 

100 

75 

50 

25 

0 

4000 

3000 

2000 

1000 

0 

PERCENT COVER OF BROADLEAVES AT FIRST CUTTING (6/8/20) 

No pre-plant treatment Glyphosate pre-plant Tillage pre-plant 

Raptor In-season 

PERCENT COVER OF ALFALFA AT FIRST CUTTING (6/8/20) 

No pre-plant treatment 

Glyphosate pre-plant 


No In-season control 

ALFALFA YIELDS AT FIRST CUTTING (6/8/20) 

Tillage pre-plant 

Figure 2. Effect of early weed management and follow-up in-season weed management on 

percent cover of alfalfa at first cutting. 




Figure 1. Broadleaf weed cover at first harvest as affected by pre-plant and 

in-season weed control (June 8, 2020) (all figures courtesy S. Light.) 


Figure 3. Yield of the first cutting of alfalfa as affected by affected by early season and 

in-season weed management. 

# Alfalfa plants per 20x20cm quadrant 

ALFALFA STAND COUNTS AFTER FIRST CUTTING 




Figure 4. Alfalfa stand counts at first cutting showing significant effects of early 

pre-plant treatments as well as the effect of in-season herbicide treatment. 

Stand count data was collected after first cutting (see results in Figure 4.) (All 

photos by S. Light.) 


the pre-plant weed control treatments having more 

alfalfa than the control. 

May 14, 2020 Weed Counts* 

Grasses + sedges: There were not many grasses or 

sedges in the field. 

Broadleaves: There were significantly less broadleaves 

in the plots that had pre-plant weed control 

(glyphosate or tillage) and in the plots that had 

Raptor applied in-season. 

Alfalfa: There was significantly more alfalfa in the 

plots that had pre-plant weed control (glyphosate 

or tillage) and in the plots that had an in-season 

herbicide. 

*Data not shown 

Broadleaf Weeds Dominated at First Cutting 

There were significantly more broadleaf weeds in 

the plots that had no pre-plant weed control (glyphosate 

or tillage) (Figure 1). Additionally, the plots 

that had Raptor applied in-season reduced broadleaf 

weeds down to negligible levels compared with 

no in-season treatment (Figure 1). There were not 

many grasses or sedges in the field; however, there 

were more grasses in the side of the field with no 

in-season herbicide application. 

Alfalfa Stand 

There was significantly more alfalfa at first cutting 

in the plots that had pre-plant weed control 

(glyphosate or tillage) and in the plots that had an 

in-season herbicide (Figure 2). Weeds in the no 

pre-plant treatment essentially killed many of the 

young seedlings due to weed competition. This is a 

key issue since early growth and establishment of 

alfalfa seedlings sets the stage for vigorous growth 

over many years of production. This is demonstrated 

by the number of alfalfa plants in a 20x20 

cm quadrant after first cutting (Figure 4). There 

were significant differences in the alfalfa stand after 

first cutting. With regard to pre-plant treatments, 

both glyphosate spray and tillage pre-plant significantly 

increased alfalfa stand compared to the plots 

with no pre-plant treatment. 

Enhanced Yields 

Alfalfa yields were near zero for the plots where early 

control was not applied (Figure 4). Additionally, 

yields were improved over 90% when an in-season 

weed control was applied (Figure 4). This yield data 

is only for the first cutting of the stand, not for the 

full first year of production. There were significant 

differences in alfalfa yield between pre-plant treatments 

and plots that had no pre-plant weed control 

(Figure 3). Both the glyphosate and tillage pre-plant 


treatments increased yields. In addition, 

the Raptor spray significantly increased 

yields compared to plots without 

in-season control. 

A combination of early weed control 

combined with in-season weed control 

was the most successful at controlling 

weeds and enhancing alfalfa yields. 

Biomass was separated into alfalfa 

(Figure 3, see page 18) and weeds after 

plots were hand-harvested. Alfalfa and 

weeds were then weighed separately 

by plot. There were significantly more 

weeds by weight in the side of the field 

that did not get the herbicide spray in 

season compared to the side that did 

get an herbicide spray. However, within 

one side of the field (Raptor or not), 

there were no significant differences 

by pre-plant treatment. In other words, 

even though there was more alfalfa in 

the plots with pre-plant weed control, 

there were also more weeds. The photo 

taken at harvest show how heavy the 

weed pressure was even in plots with 

Glyphosate and tillage pre-plant that 

did not have in-season herbicide application. 

When comparing plots with the same 

pre-plant treatments with or without 

in-season herbicide spray, plots that 

were tilled pre-plant did not have 

significantly different stand counts 

regardless of in-season herbicide treatment. 

However, within the plots that 

were sprayed with glyphosate pre-plant, 

those that also were sprayed with Raptor 

in-season had significantly higher 

alfalfa stand counts than those without 

in-season control. 

Conclusions 

The data shows that controlling weeds 

prior to planting, either with shallow 

tillage or an herbicide spray (glyphosate), 

will reduce weed pressure, 

increase yields and lead to a stronger 

alfalfa stand after first cutting. There 

were also differences between plots 

that got an in-season herbicide and 

those that did not. Yields were highest 

in plots that had both pre-plant weed 

control and an in-season herbicide. The 

plots with the highest stand counts after 

first cutting were also the plots that had 


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A combination of early weed control combined with in-season 

weed control was the most successful at controlling weeds and 

enhancing alfalfa yields. 

This photo taken at harvest shows how heavy the weed pressure was even 

in plots with glyphosate or tillage pre-plant that did not have in-season 

herbicide application. 

Crop Resilience 

Vineyards and orchards grow best 

in fungally dominant soil. 

Fungal networks of mycelia and 

mycorrhizae extend the reach of 

roots to access nutrients and water. 

Beneficial fungi also help suppress 

disease and mitigate abiotic stresses 

like drought, salinity and heat. 

Biological fertility programs renew 

the soil with diverse fungi, which 

increases humus and water-holding 

capacity. 

Pacific Gro provides fungal food: 

fish oil, chitin and micro-nutrients 

from the ocean. You can measure 

differences the first season, and you 

may even see mushrooms sprout or 

mycelia spread. 

Vineyards, nut orchards, citrus groves, and cherry and apple orchards have 

had remarkable success with biological fertility programs including Pacific Gro. 

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both pre-plant and in-season weed 

control. However, the stand in the preplant 

treatment plots that did not have 

an in-season herbicide application still 

had relatively high alfalfa stand counts 

after first cutting. This means that with 

early effective weed control, the alfalfa 

stand may be more robust for future 

cuttings, even if weed pressure was 

high initially. As shown in the provided 

photos, the alfalfa was robust in the 

understory of the canopy, even when 

broadleaf weeds were very large. By 

first cutting, many broad leaf weeds 

had gone to flower, so they likely would 

not return after first cutting. However, 

when included in the harvest, these 

weeds reduce quality and price of the 

hay and also contribute seed to the 

weed-seed population in the field. 

Ideally, both pre-plant and in-season 

weed control would be implemented to 

get highest yields, quality, a vigorous 

stand and ensure animal safety. However, 

growers (particularly organic) may 

be able to do a pre-plant tillage to control 

weeds and establish a good alfalfa 

stand, accept some yield reduction and 

additional weed pressure leading up 

to first cutting and then have a strong 

alfalfa stand for subsequent cuttings. 

The author would like to thank the California 

Alfalfa & Forage Association for 

funding this project and River Garden 

Farms for their collaboration on this 

project. 





Managing Soil 

Structure and Quality 

Biological Management Practices to Maximize Soil Quality 

By DR. KARL WYANT | Vice President of Ag Science, Heliae Agriculture 

Board of Directors, Western Region Certified Crop Advisers 

Management practices that 

improve soil health and soil 

quality have gained considerable 

attention over the past few years. If you 

are wondering how to get started and 

what to focus on, you have come to the 

right place! In Part 2 of this article series, 

I focus on how the living, biologic 

components of the soil, the microbes, 

directly impact your soil, including the 

structure (e.g., aggregation and pore 

space). My focus on bacteria and fungi 

in the soil is a perfect complement to 

Part 1 of this article series, where we 

explored the physical and chemical 

components behind soil structure. Part 

1 can be found in the January/February 

2021 edition of Progressive Crop 

Consultant. 

Let us kick things off with a quick 

reminder of some terminology and 

drive home the connection between 

soil quality (structure) and soil health 

(biology). 

Soil quality: This term has broad application 

on your farm. Soil quality refers 

to how well a soil functions physically, 

chemically and biologically and does 

its “job” (Figure 1). Many factors influence 

the soil quality on a farm and are 

summed up in Figure 2. In this article, 

we will focus on the biological management 

practices that maximize soil 

quality, expressed here as soil structure. 

Soil health: This term refers to the 

interaction between organisms and 

their environment in a soil ecosystem 

and the properties provided by such 

Figure 1. Holistic soil management can be used to help improve soil structure and soil quality. 

We explored the physical and chemical controls in Part 1 and explore the biological controls in 

Part 2 of this article series (all figures and tables courtesy K. Wyant.) 

interactions. When you think of soil 

health, think of the biological integrity 

of your field (e.g., microbial population 

and diversity) and how the soil biology 

supports plant growth. 

There is a direct link between soil 

health (the living component) and soil 

quality (the structural component). 

The linkage is fungi and bacteria in the 

soil and the byproducts they secrete. 

These byproducts help restore your 

soil structure (Figure 3, see page 23). 

Furthermore, well-structured soils are 

characterized by excellent soil health, 

which indicates a feedback loop between 

the soil biology and soil particles. 

But how exactly do the microbes 

put your soil back together? 

Figure 2. Crop productivity is influenced by 

several interrelated concepts, which have an 

impact on the soil quality of a field. 


Component 

Practice 

Feed Existing Biology 

Add Biology 

Mulches and Compost 

Cover Cropping 

Reduce tillage 

Glue and Nets 

Abundant and diverse soil microbial 

communities produce lots of “free”- 

services for your farm soil. When 

your soil is healthy, microbes speed up 

nutrient release rates back to the crop, 

influence the water holding capacity of 

the soil, and help restore soil structure. 

How exactly do they go about sticking 

the soil together? The answer can be 

summed up in two terms: glues and 

nets. 

When you have a healthy and abundant 

soil bacteria population, they produce 

a sticky, glue-like gel called extracellular 

polymeric substances (EPS) that 

forms a protective slime layer around 

bacteria as they grow. EPS, since it is 

sticky, acts as a glue for soil particles, 

sticking them together and improving 

overall soil structure. 

Another important group of soil 

microbes, called fungi, is most known 

Provides the soil microbiome a food source 

Provide certain species of bacteria and fungi to soil 

Provides a bulk carbon and nutrient source to the soil 

Keeps living roots in the soil and protects soil from erosion 

Helps keep soil structure and microbial communities intact 

Table 1. Practices that can help improve soil biology and improve soil structure. 

by its aboveground structures like 

mushrooms. However, most soil fungi 

exist where you cannot see them below 

ground. In the soil, fungi produce millions 

of miles of microscopic threads 

called hyphae. These structures help 

fungi find resources and grow. The 

threads also help to capture and tie 

soil particles together like a net, which 

improves soil structure. Now that you 

know the connection between your soil 

biology and soil structure, let us turn 

our attention to management practices 

that can help optimize the contribution 

of microbes to improving your farm 

soil (Table 1). 

Soil Biology Management 

Guidelines 

Feed the Soil Biology 

This might seem like an obvious 

management choice, but this practice 

is often missed in the yearly crop plan. 


With a focus on abiotic 

stress, diKaP (0-31-50) 

improves nitrogen 

metabolism that can 

lead to reduced 

incidence of hull rot. 

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Figure 3. The soil on the left has poor soil structure while the soil on the right has excellent 

aggregation and structure. The samples also have vastly different living components in the 

soil, as shown in the agar plates. The soil with the best aggregation is characterized by having 

a healthy soil microbiome (right). 

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@redoxgrows 



Your soil is teeming with fungi and 

bacteria and they are ready to go to 

work for you. The problem? They are 

starving and will go dormant on you 

until conditions improve. Research 

shows that farm soils are generally low 

in the food stuffs that microbes like to 

eat, and that food scarcity will limit 

the activity of your soil biology. The 

answer? Provide them with a regular 

installment of something they like to 

eat to keep their populations up. You 

have many choices, including microalgae, 

molasses, fish emulsions, etc. 

Add Soil Biology 

Another option is to add biology to the 

soil. I do not have space to cover all 

the products out there, but the main 

concept is to provide selected species 

of bacteria or fungi to the soil and put 

them to work for you. Keep in mind 

that the inoculant must stay alive to get 

the benefit you are looking for. This can 

be quite a challenge considering how 

sensitive microbes are to changes in 

temperature and humidity from shipping 

to storage in the farm shop to field 

application. If you choose this option, 

make sure your product is viable and 

high quality when going out into the 

field. 

Mulches and Compost 

This practice is like the first management 

suggestion but provides more 

of a “slow release” food source for the 

microbes. Not all the carbon in plant 

mulch and compost is available as 

microbial food. Instead, it must be 

chemically and physically broken down 

before the microbes can take advantage 

of it. Another advantage is that mulches 

and compost provide a nutrient 

source to the soil. A potential disadvantage 

here is that mulches and compost 

can contain excess salts and weed seeds 

if not prepared correctly. 

Reduce Tillage and Improve Soil 

Biology 

Field activities like tillage can be hard 

on your soil biology, particularly the 

soil fungi. For example, when a disk 

moves through the field, it not only 

slices through the soil (what you want 

to happen) but it also slices and dices 

through all the fungi threads you 

are trying to grow (what you do not 

want to happen.) This unintentional 

result can have a severe impact on the 

biological contribution to soil structure. 

Moreover, excessive tillage can 

crush and compact your soil structure, 

which can set you back from a physical 

management perspective. Reducing 

tillage, therefore, can improve your soil 

structure on two fronts. Talk about a 

2-for-1 deal! 

Cover Crops and Soil Biology 

The cover crop, usually grown in 

between the rows of permanent crops 

(e.g., trees and vines) or in the ‘off-season’ 

for annual crops, can be used to 

help feed soil microbes. Cover crop 

roots secrete carbon substances, called 

exudates, which can help boost the soil 

fungi and bacteria when a crop is not 

in the ground. Keeping your soil alive 

year-round is key to optimizing the 

biological contribution to soil quality. 

Fine root hairs can also tie soil particles 

together, improving soil structure and 

quality. Another two-for-one deal! 

Testing for Soil Biology 

No doubt you are familiar with soil 

tests from your favorite agricultural 

laboratory. Traditional soil tests have 

mainly focused on measuring the 

chemical constituents of the soil (e.g., 

nitrate, phosphate, etc.) or the physical 

aspects of the soil (e.g., soil texture, 

cation exchange capacity). However, as 

useful as these tests are, they fail to explain 

how “alive” the soils are. There is 

good news though! Many laboratories 

are starting to offer soil health testing 

services which can help you get a better 

understanding of the biological components 

of your soil. Certified Crop Advisors 

(CCA) help guide growers through 

which test to order and, more importantly, 

help them interpret it. Common 

tests include measurements of carbon 

dioxide respiration, extraction of DNA 

for microbial community analysis 

and even direct counting of fungi and 

bacteria populations. There are many 

choices and sound advice from an 

experienced crop advisor that can help 

direct you down the right path and 

reduce the learning curve. 

Conclusion 

Biological factors can have a profound 

impact on overall soil structure and, 

thus, the soil quality of the field. Generally, 

poorly structured soils have a difficult 

time supporting optimized crop 

growth due to the severe reduction 

in water storage capacity, low oxygen, 

surface crusting and seed bed issues, 

accumulation of salinity, etc. If the soil 

looks like the example on the left side 

of Figure 3, it may be well worth your 

time and money to start implementing 

soil biology improvement practices as 

outlined in this article and revisit some 

of the physical and chemical practices 

discussed in Part 1 of this series. I 

strongly recommend that you put your 

field detective hat on to diagnose why 

your field is not performing as expected. 

A bit of detective work beforehand can 

pay off in turning your field around 

and using your input dollars most 

effectively. 

Dr. Karl Wyant currently serves as the 

Vice President of Ag Science at Heliae ® 

Agriculture where he oversees the internal 

and external PhycoTerra ® trials, assists 

with building regenerative agriculture 

implementation and oversees agronomy 

training. 

Resources 

Soil Health Partnership Blog: https:// 

www.soilhealthpartnership.org/shp-blog/ 

Soil Health Institute Blog: https://soilhealthinstitute.org/resources/ 

The Applied Side of Soil Health Measurements: 

https://phycoterra.com/ 

the-applied-side-of-soil-health-measurements-2/ 

The Connection Between Your Soil 

Structure and Soil Moisture: https://phycoterra.com/connection-between-soilstructure-soil-moisture-crop/ 

Physical and Chemical Controls of 

Soil Structure: http://progressivecrop. 

com/2021/01/managing-soil-and-structure-quality/ 





Avocado Invasive Insect Pests 

Current, Potential and Recent Threats to 

Southern California’s Avocado Industry 

By SONIA RIOS | UCCE Subtropical Horticulture Farm Advisor, Riverside and San Diego Counties 

AKIF ESKALEN | UCCE Specialist, Grapevine, Fruit Trees and Small Fruits Pathology 

MARK S. HODDLE | UCCE Specialist, Biological Control, UC Riverside 

Globally, invasive insect pests 

cause substantial damage to agricultural 

crops and natural environments. 

In the U.S. alone, crop and forest 

production losses from invasive insects 

and pathogens have been estimated at 

almost $40 billion per year (Pimentel et 

al. 2005). On average, a new non-native 

invertebrate is introduced into California 

every 40 days. With respect to insects and 

mites, about one-third of these become 

pests (Dowell et al. 2016), and economic 

losses in California are estimated at more 

than $3 billion per year (Metcalf 1995). 

Rapid growth of U.S. demand for fresh 

avocados has increased the fruit’s prominence 

in retail sales and diets. California 

is the largest producer of avocados grown 

in the U.S. The value of U.S. avocado 

production measured at approximately 

$392 million in 2017, (NASS, 2018). There 

are more than 3,000 avocado growers 

in the state farming on approximately 

50,000 acres of land, with Ventura County 

leading the state in most acres planted 

and harvested in recent years (California 

Avocado Commission [CAC], 2020). 

California avocados are particularly 

special because less than 1% of the state 

is suitable for growing them. A healthy, 

single ‘Hass’ avocado tree can produce 

up to 200 pounds of fresh fruit each 

year, which is ~500 pieces. In 2018 alone, 

California produced around 350 million 

pounds. Avocados are considered a 

specialty crop and are not cheap to grow 

because of water and land costs, and 

fruit therefore usually demands a high 

premium price. 

Traditionally, insecticide use in California 

avocado orchards has been minimal 

due to relatively few pest species, which, 

for the most part, have been under adequate 

levels of biological control (Hoddle 

2005). However, due to the increase of 

international trade, illegal importation 

and the smuggling of foliage, branches 

with leaves, whole plants and budwood, 

invasive insect and mite pests have begun 

to threaten the economic viability of 

avocado production in California. 

Polyphagous and Kuroshio 

Shot Hole Borers 

Polyphagous Shot Hole Bore (PSHB) 

is an invasive ambrosia beetle from 

Southeast Asia that was first detected in 

Los Angeles County in 2003 (Gomez et al. 

2018, Rabaglia et al. 2006). PSHB is a pest 

of great concern in Southern California 

as it can attack over 300 tree species and 

reproduce on a subset of these that are 

capable of supporting beetle reproduction 

and growing the fungi that cause 

fusarium dieback. 

PSHB has a strong symbiotic relationship 

with several fungi, including Fusarium 

euwallaceae and Fusarium kuroshium, 

the causal agent of Fusarium Dieback 

(FD) disease (Eskalen et al. 2013). The 

list of reproductive hosts includes several 

native oaks, maples, sycamores, willows 

and avocado. The fungus disrupts the 

vascular transport of water and nutrients 

on their host tree that eventually causes 

branch dieback. The most common 

symptoms of the disease include sugar 

or gum exudates, dieback, wilt and 

ultimately host tree mortality. Reports 

of dieback symptoms in El Cajon, San 

Diego County led to the discovery of 

another species, the Kuroshio shot hole 

borer (KSHB) in 2013. 

KSHB is also present in commercial 

avocado orchards in San Diego County. 

KSHB was originally limited to the San 

Diego region but has since spread to 

Orange, Los Angeles, Ventura and Santa 

Barbara counties. Presumably, PSHB and 

KSHB were introduced accidentally into 

Southern California via wooden products 

and/or shipping material (e.g., pallets and 

dunnage) from Southeast Asia. KSHB is 

morphologically indistinguishable from 

PSHB, but species can be separated using 

molecular techniques. 

The fungus gets into the woody tissue of 

the tree when a female PSHB excavates a 

gallery and inoculates the gallery walls 

with fungal spores that it carries in special 

structures called mycangia (Beaver, 

1989). The female PSHB and her offspring 

feed exclusively on the fungal spores. 

PSHB adults engage in sibling mating 

within the natal gallery. Offspring sex 

ratios are female biased to maximize reproductive 

output such that one male can 

inseminate many of his female siblings. 

Once fully developed and mated, female 

PSHB exit their natal gallery to start a 

gallery of their own and repeat the cycle. 

Unlike their sisters, male PSHB do not 

disperse since they are not capable of flying 

and do not possess mycangia, which 

are specialized structures for fungus 

storage. 

Pesticide efficacy may be limited, and 

this is attributed to the fact that PSHB 

feeds on fungi and not directly on wood 

tissue. This reduces exposure to active 

ingredients when feeding (Eatough 

Jones et al. 2017). Cultural management 

practices include: 1) removal of infected 

branches to reduce local beetle numbers 

and fungal spread in the infested area; 

2) chipping (< 1 inch) and solarizing infested 

wood; and 3) avoiding movement 

of infested materials to new areas (if 


A female PSHB boring (photo by A. Eskalen.) 

Beetle gallery formation in an avocado branch (photo by 

A. Eskalen.) 

transportation of materials is necessary, 

it must be covered(UC IPM 2017). 

These management strategies can perhaps 

abate the severity of local infestations. 

Also, limiting the spread of infected/infested 

trees include minimizing firewood 

transportation. Sterilizing pruning 

tools with household bleach or another 

cleaning solution can reduce the spread 

of the FD pathogen. The PSHB was found 

in Israel in 2009 in commercial avocado 

orchards where it damages trees. To date, 

there has been no avocado tree fatality 

due to the PSHB or FD in California. For 

more information regarding PSHB, visit 

ucanr.edu/sites/pshb/. 

Redbay Ambrosia Beetle 

and Laurel Wilt Complex 

An invasive ambrosia beetle, the redbay 

ambrosia beetle (RAB; Xyleborus glabratus) 

is a serious pest currently spreading 

through the Florida avocado industry 

and has been responsible for significant 

yield reductions since its discovery in 

2005. The beetle was first detected in the 

U.S. in Port Wentworth, Ga. in 2002 and 

was probably introduced via infested 

wooden packaging material (Crane 2011). 

This beetle has been slowly spreading 

across the southeastern U.S. and is 

currently found as far west as east Texas. 

Therefore, California growers need to 

be aware that this pest-disease complex 

may spread to California avocados. What 

makes this complex dangerous is that the 

vector, RAB, has a symbiotic relationship 

with the fungal pathogen Raffaelea 

lauricola that causes Laurel Wilt Disease 

(LWD). Native to Southeast Asia, RAB 

has similarities to our current ambrosia 

pest, PSHB. However, the fungus as- 




sociated with LWD is unlike the disease 

here in California. Trees become infected 

when female beetles attack host trees and 

introduce the pathogen into the xylem 

while boring their galleries. The infection 

restricts the flow of water in the tree, 

induces a black discoloration in the outer 

sapwood and causes the leaves to wilt. 

Tree mortality is so rapid that leaves do 

not fall from dying branches. 

Symptoms of RAB beetle and LWD infestations 

include (Carrillo et al. 2017): 

• Wilting of leaves and young stems. 

You can usually see dead leaves 

hanging on branches. 

• Color change in leaves from light 

green to dark purplish green or 

greenish brown. 

• Stem and limb dieback. 

• Trunk and major limbs that 

show dried sap which has a white 

appearance and is a crystalline, 

powder-like material. 

• Dark streaks in the sapwood. 

Normally sapwood should be white 

to yellowish white in coloration 

with no dark staining or streaking. 

To check for this symptom simply 

remove a section of the bark to 

check for discoloration, which, 

if present, may indicate fungal 

infection. 

• Small, dark holes in the sapwood 

and what looks like loose wood 

dust and frass indicate wood boring 

beetles are present. 

LWD affects redbay (Persea borbonia) 

and other tree species of the Laurel 

family (Lauraceae), including avocado. 

R. lauricola is introduced into host trees 

when adult RAB colonizes a tree. Adult 

RAB are very small (~1/16-inch-long), 

dark brown to black in color and spend 

most of their life within the tree. Larvae 

are white, legless grubs with an amber 

colored head capsule and are found within 

galleries throughout infected trees. Female 

beetles can produce flightless male 

offspring without mating, but females 

may mate with their male offspring or 

brothers to produce males and females. 

Females greatly outnumber males in 

populations. In the Southeast U.S., 

RAB’s lifecycle from egg to adult appears 

to take 50 to 60 days, and there appear to 

be multiple overlapping generations per 

year (Hanula et al. 2008). Female beetles 

emerging from galleries may reinfest the 

same tree or disperse in search of new 

hosts. Host trees can remain standing 

for years and may continue to serve 

as host material for beetles for several 

months after initial colonization. Flight 

activity peaks in the late afternoon and 

early evening. 

It is known that ambrosia beetles are 

notoriously difficult to control with 

insecticides because they are protected 

from residues by living inside the tree 

most of their life versus being outside 

the tree. RAB can fly short distances, 

but LW fungus spreads more quickly 

through the movement of insect-infested 

plant material, such as firewood. 

Additionally, the pathogen also spreads 

to other ambrosia beetle vectors. This 

happens when beetles feed on diseased 

trees and become contaminated with 

spores of R. lauricola. Spread can also 

occur through root grafting between 

trees. Sanitation is the most effective way 

to manage this problem. Scouting for 

wilted branches and quickly removing 

them has been key to successful early 

intervention and eradication. 

It has been suggested to remove symptomatic 

trees immediately upon their 

identification. However, once the 

appearance of frass and streaks start to 

show in the wood, this is a sign that the 

tree has already been infected and has 

been for some time. As soon as a grower 

sees the wilt in the branches, it’s time 

to move quickly. Verticillium wilt and 

Phytophthora root rot can be mistaken 

for LW, so avocado growers should check 

for these diseases before removing trees. 

The Florida avocado industry has 

implemented a universal detection and 

suppression program with the goal of 

preventing or limiting the incidence of 


Severe Laurel wilt vascular staining on avocado 

(photo by A. Eskalen.) 

Laurel wilt branch die back on avocado (photo by 

S. Rios.) 

RAB entry holes in avocado (photo by S. Rios.) 

The presence of frass indicates the presence of 

RAB (photo by A. Eskalen.) 


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LW in commercial groves and depressing 

ambrosia beetle populations (Carrillo et. 

al 2017). Surveying for the symptoms of 

LW is a key component to limiting the 

spread of the disease. Growers and their 

workers should survey groves weekly or 

more often if an infestation is detected 

in an adjacent grove. Early detection, 

removal and destruction of LW affected 

trees is the most important practice for 

controlling LW. 

Contact insecticides are ineffective 

because the pathogen vectors (i.e., the 

ambrosia beetles) are primarily inside the 

tree. The first goal is to avoid infestation 

with the beetles by maintaining a healthy 

tree as stressed trees are more attractive 

to colonizing beetles. Beetles prefer trees 

in orchards that have dense canopies 

with overlapping leaves and branches. 

Chipping infected trees is effective in reducing 

the spread of the disease. However, 

chips must be as small as possible (one 

square inch or smaller) and dried quickly 

so that the wood is not conducive to fungal 

growth. A potential drawback to this 

method is that the aroma of the chipped 

wood can attract other wood boring 

insects. Research in Florida is currently 

being conducted to determine if different 

Avocado lace bug adult and eggs (photo by M. Hoddle.) 

commercial formulations of insecticides 

can be effective in controlling the beetle. 

For more information regarding LW and 

RAB, please visit sfyl.ifas.ufl.edu/miami-dade/agriculture/laurel-wilt---a-disease-impacting-avocados/. 

Avocado Lacebug 

The avocado lacebug (ALB), Pseudacysta 

perseae (Hemiptera: Tingidae), was first 

detected in California on backyard avocado 

trees in Chula Vista and National 

City, San Diego County in 2004. This 

pest was first described in Florida in 1908 

and has since been reported from Mexico, 

Guatemala, Puerto Rico, Jamaica, the 

Dominican Republic and parts of northeastern 

South America. The native range 

of ALB is uncertain. Molecular studies 

suggest that the western areas of Mexico 

may be the evolutionary center of origin 

for this pest and it was spread unintentionally 

from this area, probably on avocado 

trees into eastern Mexico, Florida 

and the Caribbean (Rugman-Jones et al. 

2012). 

After a lull of approximately 13 years, 

reports started coming of ALB damage 

to avocados outside of San Diego. In October 

2017, well established, reproducing 

populations of lace bugs were confirmed 

in commercial Hass avocado groves in 

Oceanside and De Luz in San 

Diego County and in Temecula 

in Riverside County (CAC, 2017). 

Around this time, infestations 

were reported from backyard 

avocados in Culver City in Los 

Angeles County. Genetic analysis 

suggested that these new, more 

damaging populations of ALB 

were different to those originally 

detected in San Diego in 2004, and 

it’s likely that a second introduction 

of ALB into California has 

occurred, possibly from Florida 

(Rugman-Jones and Stouthamer 

unpublished molecular data). 

ALB has been recorded feeding 

on avocado, red bay and camphor, 

which are all in the Lauraceae 

family. 

Avocado lace bug is a true bug 

with sucking mouth parts. Lace 

bugs use these needle-like mouthparts 

to feed on the undersides of 

leaves. Through feeding, leaf cells and 

pierced cell contents are extracted and 

ingested, preventing photosynthesis. 

Adult avocado lace bugs are small, 

winged insects, about 2 mm in length 

(slightly longer than 1/16 in), with black 

bodies, yellow legs and antennae, and are 

visible to the naked eye (UC IPM 2021). 

ALB live in colonies on the lower surfaces 

of mature leaves, often adults, eggs and 

nymphs are found together. Eggs are 

laid in an irregular pattern, sometimes 

in loose rows, attached to the lower leaf 

surface and are covered with irregular 

globules of a black, sticky, tar-like substance 

excreted by adults. To the naked 

eye, eggs will appear like grains of black 

pepper or dirt. 

Eggs hatch into wingless nymphs that are 

capable of walking. Nymphs go through 

a gradual metamorphosis, shedding their 

exoskeleton several times as they grow in 

size, finally developing wings and becoming 

flying adults. Nymphs are dark redbrown 

to black and covered with spines. 

They feed for approximately two to three 

weeks before maturing into adult males 

and females which mate, and females 

then lay eggs, starting the cycle over. In 

California, ALB populations tend to peak 

over early summer, around June, then 

decline in fall, sometime around September 

(Humeres et al. 2009). 

ALB restrict their feeding to the undersides 

of leaves. Feeding initially causes 

small white or yellow spots on the 

surface of the leaves as individual cells 

dry out. These necrotic areas look like 

tip-burn caused by excessive salts, but in 

this case, the necrotic areas are islands 

of dead tissue in the interior of the leaf 

surrounded by living tissue. It is suspected 

that feeding damage can provide 

entrance for pathogenic fungi, in particular 

Colletotrichum spp., which are leaf 

anthracnose fungi. As lace bug colonies 

grow, brown necrotic areas develop 

where there has been heavy feeding damage. 

Heavy feeding can cause striking leaf 

discoloration and early leaf drop (Hoddle 

2004; Hoddle et al. 2005). Avocado lace 

bug nymphs and adults do not feed on 

fruit. However, heavy feeding damage to 

leaves will likely have a detrimental effect 

on yield, which may result from the loss 


of photosynthetic capacity in damaged 

leaves. 

Relatively little is known about biology 

and ecology of ALB in California. In 

Florida, the most important biological 

control agents are two egg parasitoids 

including Oligosita sp. (a Trichogrammatid 

wasp) and an unidentified mymarid 

wasp. Green lace wing larvae and other 

generalist predators are also thought to 

be important natural enemies. A predatory 

thrips, Franklinothrips vespiformis, 

is reported to be the most important 

natural enemy of the avocado lace bug in 

the Dominican Republic and is similarly 

abundant on ALB-infested avocados in 

Escuintla Guatemala. 

Insecticide treatments for other sucking 

pests currently registered for use on 

avocado in California will likely provide 

control of avocado lace bugs (Hoddle et 

al. 2005). In a trial reported in 1998, J. E. 

Peña, University of Florida (UF), showed 

that citrus oil, M-Pede (insecticidal 

soap) and Mycotrol (a Beauveria fungal 

species) all controlled lace bug, but it was 

not indicated how long the effect lasted. 

Researchers at UF have shown that citrus 

oil and M-Pede provided short-term lace 

bug control. Results of small tree trials 

or weathered residue tests have indicated 

that carbaryl, imidicloprid, cyfluthrin, 

carbaryl, fenpropathrin and malathion 

provide excellent control of avocado lace 

bug nymphs. Spinosad, abamectin and 

mineral oil are much less effective at 

providing control (Humeres et al. 2009b; 

Byrne et al. 2010). For more information 

on lace bugs, please visit biocontrol.ucr. 

edu/avocado-lace-bug. 

Severe feeding damage to avocado leaves caused by avocado lace bug (photo by M. 

Hoddle.) 

Ideally, finding a new pest species in the 

early stages of the invasion and quickly 

containing and treating the new infestation 

may reduce costly long-term 

management, especially if eradication is 

possible. Rapid and decisive containment 

actions are an important consideration as 

controlling invasive pests, especially fruit 

feeders, in California avocado orchards 

will always be a challenge and expensive 

should they establish widely. 

References 

Byrne, F. J., Almanzor, J., Tellez, I., Eskalen, A., Grosman, D. M., & Morse, J. G. 2020. 

Evaluation of trunk-injected emamectin benzoate as a potential management 

strategy for Kuroshio shot hole borer in avocado trees. Crop Protection, 132, 105136. 

Byrne, F. J., Humeres, E. C., Urena, A. A., Hoddle, M. S., and Morse, J. G. 2010. Field 

evaluation of systemic imidacloprid for the management of avocado thrips and 

avocado lace bug in California avocado groves. Pest management science, 66(10), 

1129-1136. 

Carrillo, D., J. Crane, R. Ploetz, E. Evans, and J. Wasielewski. 2017. Brief Update to 

Laurel Wilt Recommendations – Ambrosia Beetles. Univ. of Florida, IFAS Extension 

Notice. 

Crane, J. (2011) Laurel Wilt and the Redbay Ambrosia Beetle threaten Florida’s 

avocado and native trees in the Laurel Family. Univ. of Florida, IFAS Extension 

Homeowner informational brochure. 

Coleman, T. W., Poloni, A. L., Chen, Y., Thu, P. Q., Li, Q., Sun, J., and Seybold, S. J. 2019. 

Hardwood injury and mortality associated with two shot hole borers, Euwallacea 

spp., in the invaded region of southern California, USA, and the native region of 

Southeast Asia. Annals of Forest Science, 76(3), 1-18. 

Hughes, M.A., Smith, J.A., Ploetz, R.C., Kendra, P.E., Mayfield, A.B., Hanula, J., Hulcr, 

J., Stelinski, L.L., Cameron, S., Riggins, J.J. and Carrillo, D. 2015. Recovery plan for laurel 

wilt on redbay and other forest species caused by Raffaelea lauricola and 

disseminated by Xyleborus glabratus. Plant Health Progress, 16(4), pp.174-210. 

Humeres, E. C., Morse, J. G., Stouthamer, R., Roltsch, W., & Hoddle, M. S. 2009a. 

Detection surveys and population monitoring for Pseudacysta perseae on 

avocados in southern California. Florida Entomologist 92(2): 382-385. 

Humeres, E. C., Morse, J. G., Stouthamer, R., Roltsch, W., & Hoddle, M. S. 2009b. 

Evaluation of natural enemies and insecticides for control of Pseudacysta 

perseae (Hemiptera: Tingidae) on avocados in Southern California. Florida 

Entomologist, 92(1), 35-42. 

Lu, M., Hulcr, J., and Sun, J. 2016. The role of symbiotic microbes in insect invasions. 

Annual Review of Ecology, Evolution, and Systematics, 47, 487-505. 

Mayfield, A.E. III, Barnard, E.L., Smith, J.A., Bernick, S.C. , Eickwort, J.M., and T.J. 

Dreaden. 2008. Effect of propiconazole on laurel wilt disease development in redbay 

trees and on the pathogen in vitro. Arboriculture & Urban Forestry 35: 317-324 

Mayorquin, J. S., Carrillo, J. D., Twizeyimana, M., Peacock, B. B., Sugino, K. Y., Na, 

F., and Eskalen, A. 2018. Chemical management of invasive shot hole borer and 

Fusarium dieback in California sycamore (Platanus racemosa) in southern 

California. Plant disease, 102(7), 1307-1315. 

Mead, F. W., and Peña, J. E. 2016. Avocado lace bug, Pseudacysta perseae 

(Heidemann)(Insecta: Hemiptera: Tingidae). Entomol. Circ, (346). 

Metcalf, R. L. 1995. Invasion of California by exotic insects. California Agriculture 

49(1): 2. 

Pimentel D, Zuniga R, and Morrison D. 2005.Update on the environmental and 

economic costs associated with alien-invasive species in the United States. Ecol 

Econ 52(3):273–288. 

Ploetz, R. C., Pérez‐Martínez, J. M., Smith, J. A., Hughes, M., Dreaden, T. J., Inch, S. A., 

and Fu, Y. 2012. Responses of avocado to laurel wilt, caused by Raffaelea lauricola. 

Plant Pathology, 61(4), 801-808. 

Rios, S., B. Faber, P. Mauk, A. Eskalen, and M.L. Arpaia. 2018. Redbay Ambrosia Beetle 

Poses Potential Threat to California’s Avocado Industry. California Association of 

Pest Control Advisors. February 2018. 22(1):36-38, Pp 36-38. 

Proactive Management 

and Early Detection 

The concept of early detection and rapid 

response is fundamental to effective invasive 

species management. Developing 

collaborative relationships with avocado 

research colleagues in different countries 

can provide insight into new potential 

pest problems that could eventually find 

their way to California (Hoddle et al. 

2009). Developing this idea further can 

result in the development of proactive 

biological control and IPM programs in 

advance of the anticipated arrival of new 

pest species (Hoddle et al. 2018). 

Dowell, R. V., R. J. Gill, D. R. Jeske, and M. S. Hoddle. 2016. Exotic macro-invertebrate 

invaders in California from 1700 to 2015: An analysis of records. Proceedings 

of the California Academy of Sciences Series 4 63(3): 63-157. 

Hanula, J.L, Mayfield, A.E. III, Fraedrich, S.W., and Rabaglia, R.J. 2008. Biology and 

host associations of the redbay ambrosia beetle, (Coleoptera: Curculionidae: 

Scolytinae), exotic vector of laurel wilt killing redbay trees in the southeastern 

United States. Journal of Economic Entomology 101: pp. 1276-1286. 

Hoddle, M. S. 2004. Invasions of leaf feeding arthropods: why are so many 

new pests attacking California-grown avocados? California Avocado Society 

Yearbook, 87, 65-81. 

Hoddle, Mark S., J. G. Morse, Richard Stouthamer, Eduardo Humeres, Gilsang Jeong, 

William Roltsch, Gary S. Bender. 2005. “Avocado lace bug in California.” California 

Avocado Society Yearbook 88: 67-79. 

Hoddle, M. S., Arpaia, M. L., and Hofshi, R. 2009. Mitigating invasion threats to the 

California avocado industry through collaboration. Calif. Avo. Soc. Yrbk., 92, 43-64. 

Hoddle, M. S., K. Mace, and J. Steggall. 2018. Proactive biocontrol: A cost effective 

management option for invasive pests. California Agriculture 72(3): 1-3. 

Rivera, M. J., Martini, X., Conover, D., Mafra-Neto, A., Carrillo, D., & Stelinski, L. 

L. 2020. Evaluation of semiochemical based push-pull strategy for population 

suppression of ambrosia beetle vectors of laurel wilt disease in avocado. Scientific 

reports, 10(1), 1-12. 

Rugman-Jones, P. F., M. S. Hoddle, P. A. Phillips, G. Jeong, & R. Stouthamer. 2012. 

Strong genetic structure among populations of the invasive avocado pest 

Pseudacysta perseae (Heidemann) (Hemiptera: Tingidae) reveals the source 

of introduced populations. Biological Invasions 14: 1079-1100. 

University of California Integrated Pest Management Guidelines for Avocado 

Accessed 20 March 2021. 

Umeda, C., Eskalen, A., and Paine, T. D. 2016. Polyphagous shot hole borer and 

Fusarium dieback in California. In Insects and diseases of Mediterranean forest 

systems (pp. 757-767). Springer, Cham. 






A Guide to Soil Health Testing and 

Interpretation 

By ERYN WINGATE | Agronomist, Tri-Tech Ag Products, Inc. 

Commercial farms throughout 

the U.S. consistently turn out 

impressive yields, supplying the 

nation and the world with quality fruits, 

vegetables and staple grains. However, 

every year we lose organic matter and 

watch topsoil erode with wind and 

runoff. Heavy tillage, powerful biocides 

and mineral fertilizers support high 

production even on suboptimal ground. 

Safer crop protection products and efficient 

fertigation practices significantly 

contribute to extending the longevity of 

America’s agricultural lands, yet growers 

still struggle to maintain yields on tired, 

YOU STICK TO 

GROWING. 

WE STICK TO 

YOUR SOIL. 

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viability of your older orchards with PhycoTerra ® . 

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NAVEL ORANGEWORM MANAGEMENT 

disease ridden and salt affected soils. 

Tillage, poor water quality, drought 

and soil borne disease slowly degrade 

soil health. Growers must invest in 

more water, fertilizer and pesticides to 

maintain their yields and crop quality 

on declining ground. 

Organic Matter and 

Regenerative Practices 

Healthy soils are well aerated, have 

good water and nutrient holding capacity, 

have little to no disease pressure 

and house beneficial microbial ecosystems. 

Each positive attribute relies 

on soil organic matter. Annual net 

carbon loss drives soil degradation and 

threatens our country’s food security. 

Tillage is one of the main practices 

contributing to organic matter loss. 

Turning the soil introduces an influx 

of oxygen, temporarily accelerating 

microbial activity. Bacteria and fungi, 

no longer limited by O 2 

availability, 

rapidly feed on organic matter, releasing 

carbon dioxide to the atmosphere 

as they respire. Tillage increases soil 

carbon loss beyond annual carbon gain. 

Reducing tillage, or converting to a notill 

system, can reverse carbon loss and 

begin rebuilding soil organic matter. 

Other practices, such as cover cropping, 

intercropping and composting, also 

contribute to carbon sequestration. 

Specialized agronomists can assist 

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Physical 

Chemical 

Biological 

Indicator 

Available Water Capacity 

Surface Hardness 

Subsurface Hardness 

Aggregate Stability 

Bulk Density 

Water Infiltration 

Indicator 

Electrical Conductivity (EC) 

Sodium Absorption Ratio (SAR) 

pH 

Essential Nutrients (N, P, K, Ca, 

Mg, S, etc.) 

Heavy Metals 

Cation Exchange Capacity 

Indicator 

Organic Matter 

(combustion) 

Soil Protein Index 

Soil Respiration 

Water Extractable Organic Carbon 

Microbially Active Carbon (%MAC) 

Water Extractable Organic Nitrogen 

Soil Health Metrics 

Active Carbon (potassium permanganate 

oxidation) 

Phospholipid Fatty Acid Analysis (PLFA) 

Microscopy 

Genomics 

Enzymes - B-Glucosidase, N-Acetyl-B-D 

Glucosaminidase, Phosphomonoesterase, 

arylsulfatase 

Description 

Measures the amount of water soils can hold and 

release to plant roots. Soils with higher OM have 

higher AWC. 

Measures compaction at the soil surface implicating 

susceptibility to runoff. 

Measures soil compaction between 6 to 18 inches. 

Measures how well soil aggregates stick together 

when struck by simulated rain drops. Soils with better 

aggregate stability resist erosion and generally have 

good water infiltration and aeration. 

Indicates soil structure, compaction, and organic 

matter content. Soils with high bulk density may have 

poor structure, compaction, and low organic matter. 

Measures the soil's ability to absorb water. 

Description 

Measures overall soil salinity 

Calculation comparing sodium to calcium and 

magnesium content to determine soil sodicity. 

Soil acidity and alkalinity influence nutrient availability 

Macro and micronutrient concentrations are 

measured to determine fertilization requirements and 

address potential deficiencies or toxicities. 

Measured to determine presence of metals that may 

harm plant, animal, or human health. 

Measures the soil's ability to retain essential nutrients. 

Description 

Measures the quantity of all carbon containing 

materials in the soil. 

Measures the fraction of organic matter containing 

amino acids, peptides, and proteins. Organic 

nitrogen availability influences the soil's nitrogen 

mineralization potential. 

Measures microbial activity upon rewetting oven 

dried soil. 

Small fraction of Soil Organic Matter that is readily 

available for microbial consumption. 

Percentage of WEOC used by microbes during the 

soil respiration test. High values above 80% indicate 

that microbial activity may become limited by carbon 

availability and the soil would benefit from increasing 

carbon inputs. 

Includes proteins and amino acids available for 

microbial use. Higher WEON levels indicate better 

nitrogen mineralization potential and decreases 

mineral N fertilizer requirement. 

Carbon readily available for microbial decomposition. 

Estimates the quantity and type of bacteria, fungi, and 

other microbes in the soil. 

Microorganism identification 

DNA sequencing to determine microbial genera and 

species present in the soil. 

Enzymes indicate microbial community composition 

and the soil's capacity to cycle nutrients. 

Note: This is not an exhaustive list. Contact your local soil health test lab to inquire about the soil health metrics they offer. 


growers in transitioning to a suite of 

practices to begin rebuilding soil. 

No-till cover cropped systems represent 

the gold standard for carbon sequestration 

and soil health, yet logistical and 

economic factors prevent many growers 

from adopting regenerative practices. 

When cover cropping and no till are 

unfeasible, growers can support healthy 

microbial communities by applying 

carbon rich liquid amendments and 

biostimulants. Many organic fertilizers 

and amendments contain high levels of 

carbon, amino acids and metabolites 

to support beneficial microbial activity 

during crop growth. Carbon-rich 

fertilizers made from food scraps feed 

the soil microbiome while providing a 

societal benefit by diverting waste from 

landfills. Liquid organic fertilizers, 

compost and other amendments can 

improve soil fertility, mitigate salinity 

and enhance the crop’s stress tolerance. 

No matter where your farm lies on the 

sustainability spectrum, you can monitor 

and manage the land to improve its 

long-term production capacity. 

Soil Health Metrics 

Soil health testing can guide management 

decisions and gauge progress after 

implementing new practices. Many 

commercial and university labs provide 

soil quality panels to assess a wide 

array of metrics influencing the soil’s 

production capacity and environmental 

impact. Some labs offer soil health 

assessment frameworks that rate soil 

health based on results for several key 

indicators. Lab test results for each 

indicator are mathematically transformed 

into unitless scores reflecting 

the level of functionality. Scores for 

each indicator are combined to give an 

overall soil health rating. Widely respected 

soil health frameworks include 

the Cornell Soil Health Assessment, the 

Soil Management Assessment Framework 

(Andrews et al., 2004) and the 

Haney Test provided by Ward Laboratories. 

Metrics included in the assessments 

vary between labs, but they all aim to 


include physical, chemical and biological 

components. Familiar measurements 

including pH, electrical conductivity 

(EC) and essential nutrients 

appear on soil health panels as do 

traditional field evaluations like water 

infiltration and wet aggregate stability. 

Biological indicators include combustible 

soil organic matter, water soluble 

organic carbon and soil respiration. 

Several biological indicators must be 

viewed together to accurately interpret 

field conditions. For instance, increased 

microbial respiration does not always 

indicate improved soil health. High 

respiration rates combined with high 

organic matter likely indicate good soil 

health, but when the soil shows high 

respiration and low organic matter, the 

microbes may be burning soil carbon 

faster than it can be captured. Respiration 

that outpaces carbon sequestration 

leads to organic matter loss and soil 

degradation. 

Advances in Biological Testing 

Other biological metrics provide 

insight into nutrient cycling, disease 

pressure and crop stress tolerance. Enzyme 

analysis indicates the microbial 

community’s capacity to mineralize N, 

P, K and micronutrients. Pathologists 

can diagnose fungal, bacterial, nematode 

and viral pathogens so that growers 

can choose the right fumigants and 

crop rotations to keep disease pressure 

in check. 

Phospholipid Fatty Acid Analysis 

(PLFA) helps determine the abundance 

and types of microbes in the soil. Identifying 

some of the beneficial microbes 

helps us predict the soil’s ability to inhibit 

disease, enhance crop growth and 

increase nutrient availability. Recent 

advances in genomics offer exciting 

opportunities to sequence all the DNA 

found in a soil sample and map microbial 

community composition and 

functioning. Genomics offer a more 

comprehensive analysis of microbial 

community than PLFA can provide. 

Tracking shifts in the microbiome may 

help determine how land management 

influences the soil’s trajectory towards 

improved sustainability. 

Choosing Soil Health Indicators 

Healthy soils share many common 

characteristics, but growers may 

prioritize some attributes over others 

depending on their needs. Growers can 

select soil health indicators relevant to 

their unique goals, production system, 

climate and soil type. Farmers converting 

to no-till can monitor progress 

by measuring organic matter. Those 

who continue tilling but begin cover 

cropping may not observe significant 

OM increases, but they might find 

decreased compaction and improved 

soil aggregate stability. Biostimulant 

and organic amendment efficacy may 

be measured by analyzing enzymatic 

activity and changes in the soil microbiome. 

Soil health tests are accessible, affordable 

and offer practical insights into 


Helping Farmers Grow NATURALLY Since 1974 

FEATURING: 

Office: 559-686-3833 Fax: 559-686-1453 

2904 E. Oakdale Ave. | Tulare, CA 93274 

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“ 

No matter where your farm lies 

on the sustainability spectrum, 

you can monitor and manage the 

land to improve its long-term 

production capacity. 

how farming practices affect the soil’s 

long term production capability. Track 

progress by annually measuring soil 

health indicators most likely to change 

according to the management practices 

implemented. Every farm can 

contribute to agricultural sustainability 

by adopting simple practices like 

applying carbon-based amendments 

or launching advanced regenerative 

programs such as no-till and intercropping. 

Soil health can also improve by 

knocking out disease pressure with soil 

fumigation and allowing beneficials to 

repopulate. Soil health tests can guide 

management decisions at every level to 

ensure that your effort and investment 

brings in quality crops every year. 

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Eryn Wingate is an agronomist with 

Tri-Tech Ag Products, Inc. in Ventura 

County, California. Eryn provides soil 

health and nutrient management consulting 

services to support quality crop 

production while meeting sustainability 

and environmental protection goals. 

Citations & Resources 

Andrews, S.S., Karlen, D.L., and Cambardella, C.A. 

2004. The soil management assessment framework: 

a quantitative soil quality evaluation method. Soil 

Science Society of America Journal 68: 1945-1962. 

Moebius-Clune, B.N. et al. 2016. Comprehensive 

Assessment of Soil Health – The Cornell Framework 

Manual, Edition 3.1, Cornell University, 

Geneva, NY. 

Soil Health Institute – North American Project 

to Evaluate Soil Health Indicators: soilhealth- 

Natural Resources Conservation District Soil 

Health Assessment Resources: nrcs.usda.gov/ 

institute.org/north-american-project-to-evalu- 

ate-soil-health-measurements/ 

wps/portal/nrcs/detail/soils/health/assessment/?cid=stelprdb1237387 

Ward Laboratories Haney Test Information: wardlab.com/haney-test/ 

EPA Reg. No. 264-616-87865 

Belchim Crop Protection USA, LLC 

2751 Centerville Road | Suite 100 

Wilmington, DE 19808 

Phone: 855-445-7990 

Email: info.usa@belchim.com 





May/June 2021 


FEATURED ARTICLES: 

The Potential of Ultraviolet Light to Suppress 

Grapevine Powdery Mildew 

Pg.38 

Irrigation Scheduling In Winegrape Vineyards 

Pg.46 

Grapevine Trunk Diseases 

Pg.48 

An All New Daily Radio Show 

Available now on the MyAgLife App, Download Today


The Potential of 

Ultraviolet Light to 

Suppress Grapevine 

Powdery Mildew 

By DAVID M. GADOURY | Senior Research Associate, 

Plant Pathology and Plant-Microbe Biology Section, Cornell 

AgriTech, Geneva, NY 

Figure 1. Grape powdery mildew occupies a niche bathed in 

sunlight, and it senses and uses light to direct its development. 

Researchers are learning new ways to use that evolved process 

against the pathogen to suppress disease (all photos courtesy 

D. Gadoury.) 

Global winegrape production is 

largely based upon the production 

of the European winegrape Vitis 

vinifera, a host species comprised of cultivars 

that are all highly susceptible to 

infection by the grape powdery mildew 

pathogen Erisyphe necator as well as several 

other fungal and oomycete pathogens. 

Irrespective of the center of origin 

of Vitis vinifera or the major pathogen 

groups, the global ubiquity of both the 

host and various pathogens is now a 

fact faced by grape and wine producers 

everywhere. 

In particular, fungicidal suppression of 

grapevine powdery mildew is problematic. 

Resistance to many FRAC 

classes, including sterol demethylation 

inhibitors (DMI), strobilurins, benzimidazoles 

and succinate dehydrogenase 

inhibitor (SDHI) fungicides is sufficiently 

widespread that the forgoing 

classes are no longer effective in some 

viticultural regions. Organic production 

systems are also threatened. There are 

very few practical organic options for 

controlling powdery mildews. Many 

organic options entail undesirable 

non-target effects or are marginally 

effective. Additionally, many viticultural 

regions are located in Mediterranean 

climates with little rainfall during the 

crop production season. All of the 

foregoing creates the present situation: 

grapevine powdery mildew predominates 

as the principal threat to healthy 

fruit and foliage worldwide. 

UV Light to Suppress Pathogens 

Nearly all of the biomass of powdery 

mildews is wholly external to the host 

(Figure 1). They live in a world bathed 

in sunlight throughout the disease 

process. With the exception of the 

walls of their overwintering structures 

(chasmothecia), they possess none 

of the pigmentation that would offer 

protection from biocidal wavelengths 

of the solar spectrum (wavelengths 

of UVB between 280 and 290 nm.) 

Powdery mildews are favored by shade 

and repressed to some degree by direct 

sunlight exposure. They persist in the 

above niche due in part to their ability 

to repair UV-inflicted damage to their 

DNA through a robust photolyase 

mechanism driven by blue light and 

UVA. 

In 1990, we began work that led to 

the use of germicidal UVC lamps to 

suppress E. necator. The treatments 

were effective, but UVC also damaged 



Figure 2. Researchers at Cornell used UVC applications to suppress grape powdery mildew as early 

as 1991. While effective, the treatments also caused damage to both the leaves and fruit. A breakthrough 

discovery several years later by a PhD student in Norway unlocked the key to effective 

treatments without plant injury. 

the vines, and the technology was never 

widely adopted (Figure 2). It took 20 

years before a critical breakthrough by 

a Ph.D. student in Norway (Aruppillai 

Suthparan) fundamentally changed 

how we could use UV light against 

plant pathogens. He found that if UV 

light was applied during night hours, 

we could use much lower doses than 

were required during daylight. That 

breakthrough largely resolved the issue 

of plant damage at the high UV doses 

required for daytime applications. 

Today, UV technology for plant disease 

suppression is being investigated by several 

working groups. Most exploit the 

link between darkness and the inability 

to withstand exposure to UV. When 

damage to pathogen DNA during darkness 

is not repaired within four hours, it 

is usually lethal. 

The UV spectrum used in such studies 

has ranged from a UVB waveband 

between 280 to 290 nm into the UVC 

range produced by low pressure discharge 

lamps yielding a peak output 

near 254 nm. Reduction of the severity 

of several powdery mildews has been 

attributed to direct damage to the 

pathogen by UV exposure. UVC has 

been reported to be directly inhibi- 


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© 2021 Kim-C1, LLC. Kimzall is a registered trademark of Kim-C1, LLC 


Figure 3. Tractor-drawn UVC array used in 

the first large-scale field trials on strawberries. 

Side-by-side arrays allowed two rows 

to be treated in each pass. 


tory to Botrytis cinerea on strawberry 

(Janisiewicz et al. 2016). In contrast, 

pathogens other than powdery 

mildews have been suppressed by 

exposure of their hosts to UV prior to 

inoculation, possibly due to enhancement 

of host resistance. 

The adaptation of nighttime UV treatments 

to commercial field plantings 

has necessitated the development of 

UV arrays powerful enough to apply 

effective doses at speeds that allow 

the equipment to complete treatments 

during the available night interval, 

often in late spring and early summer 

during some of the shortest nights of 

the year. Remember: we need about 

four hours of darkness after UV exposure 

in order to achieve the maximum 

suppression. A tractor-drawn UVC 

apparatus described in a report by 

Onofre et al (2019) was developed to 

suppress strawberry powdery mildew. 

This apparatus contained two hemicylindrical 

arrays of UVC lamps and was 

the basis of a later array design fitted 

to an autonomous robotic carriage 

produced by Saga Robotics, LLC. UVC 

treatments applied once or twice weekly 

at doses ranging from 70 to 200 J/m 2 

effectively suppressed strawberry powdery 

mildew (Podosphaera aphanis) to a 

degree that equaled or exceeded that of 

some of the best available fungicides. 

The potential for nighttime UV treatments 

to eliminate the threat posed by 

E. necator could greatly reduce the need 

for fungicide applications. In regions 

with higher rainfall and multiple fungal 

pathogens, the potential for nighttime 

UV treatments to remove the threat 

of powdery mildew would improve 

options for the remaining members of 

the pathogen and pest complex, such 

as downy mildew (Plasmopara viticola), 

bunch rot (Botrytis cinerea) and various 

arthropod pests. 

For all of the foregoing reasons, our 

objectives in the present study were to 

1) Determine the potential of nighttime 

UV applications to suppress grapevine 

powdery mildew; 2) Determine if UVC 

at disease-suppressive doses and frequency 

of application has any deleteri- 


Figure 4. Thorvald, an autonomous robotic 

device developed in collaboration with 

SAGA Robotics in Norway, can carry and 

power the same UV array used in tractor 

drawn devices. 

ous effects on vine growth, yield or crop 

quality; and 3) Determine if nighttime 

UV applications targeting powdery mildew 

have effects on other selected pests 

or diseases of grapevine. 

In summary, the mechanism underlying 

the success of nighttime UV applications 

is related to how pathogens deal 

with naturally-occurring ultraviolet 

light from the sun. Shorter-wave UVB 

and UVB both damage DNA in all living 

organisms. Exposure to UV causes 

thymine base pairs in the DNA to bind 

together, changing the genetic code 

to genetic gobbledygook. Pathogens 

sense visible light, but they also possess 

evolved systems that can repair the 

foregoing damage to their DNA caused 

Figure 5. Efficacy of UVC treatments for suppression 

of powdery mildew on Chardonnay grapes, 2019. 

by incoming UV. We now know that 

those biochemical and genetic repair 

systems are recharged by blue light and 

UV-A, and are reduced by red light and 

darkness. This photolyase-based repair 

mechanism effectively “unglues” the 

thymine base pairs as fast as they are 

created by UV, but the repair mechanism 

does not operate at night. 

Lamps producing UV light have been 

commonly available for over 75 years. 

Those that produce an effective wavelength 

and are powerful enough to 

be practically used against powdery 

mildews produce either UVC (100 to 

280 nm) or UVB (280 to 315 nm). Both 

UVC and UVB affect DNA in the same 

way by the aforementioned creation 

of thymine dimmers. UVB poses less 

potential to harm plants, and may 

therefore be preferred for static and 

permanent installations in greenhouses. 

However, with precise dosing, UVC 

can be used safely on even UV-sensitive 

crops. 

Low-pressure discharge lamps are the 

most common available technology. 

Low-pressure discharge UVC lamps 

are generally clear quartz-glass tubes 

containing a small amount of mercury 

vapor. Passing an electric arc through 

this vapor results in the efficient production 

of a narrow waveband centered 

on 254 nm, which is excellent for 

germicidal applications. UVB low-pressure 

discharge lamps are similar, but 

incorporate a fluorophore powder 

coating on the inside of the tube. When 

this is struck by the internally produced 

UVC, the fluorophore absorbs the 

UVC and emits the longer wavelength 

UVB. This process is also relatively 

inefficient, and nearly 95% of the 

usable germicidal energy is lost in 

the conversion from UVC to UVB. 

So, low-pressure discharge UVC 

lamps can produce much more 

usable power than comparably sized 

UVB lamps. While UV LEDs are 

available, they are presently far too 

expensive and underpowered to be 

useful for treating crops. 

Results Adapted to Grapevine 

Field trials for suppression of 

strawberry powdery mildew were 

initiated in Florida in 2017. Weekly 

applications of UVC provided suppression 

of foliar powdery mildew across 

the duration of the experiment that was 

substantially better than that provided 

by the best fungicide treatment in the 

trial, which was a combination of two 

materials sold under the trade names 

Quintec and Torino. We also confirmed 

in parallel measurements that the UV 

treatments did not reduce plant size or 

the yield of harvested berries. Continued 

trials on field plantings of strawberries 

duplicated the efficacy of the 2017 

trials. 

In our initial trials, we used a tractor-drawn 

array (Figure 3, see page 

40). Additional trials adapted modified 

designs of the original tractor-drawn 

array to an autonomous robotic 

device (Figure 4) manufactured by 

SAGA Robotics, a Norwegian company 

collaborating with our research 

group in developing this technology 

for multiple crops. The use of a robotic 

carriage provides additional flexibility 

in nighttime applications. At temperate 

latitudes, the duration of night near the 

summer solstice can be less than eight 

hours, leaving only about four hours 

during which the UV treatments could 

be applied with optimal effect. In situations 

where employing nighttime labor 

to make applications split over several 

relatively short night intervals would 

be problematic, an autonomous robotic 

device offers a practical alternative. 

In 2019, we came full circle and were 

ready to resume UV treatments on 

grapevine. As in our work on strawberry, 

we began by using a UV array and 

tractor-drawn carriage. UV Treatments 

were applied once per week at 100 or 

200 J/m 2 to Chardonnay vines that 

received no other fungicide treatments. 

Laboratory experiments had indicated 

that the UV doses used would stop 80% 

to nearly 100% of the conidia of E. necator 

from germinating. The incidence 

and severity of powdery mildew was 

assessed on leaves and fruit of UV treated 

vines, vines treated with an effective 

conventional fungicide and completely 

untreated vines. 2019 was a moderately 

severe year for powdery mildew. 




Disease Severity (%) 

50 

40 

30 

20 


12 

10 

8 

6 

4 

2 

A 

B 

C 

10 

0 

Untreated 

Oxidate 

UVC 

0 

Fungicide Untreated 100 J/m 2 200 J/m 2 

Figure 6. Foliar severity of grapevine downy mildew on Chardonnay 

vines treated weekly with UVC at 100 or 200 J/m2 compared to a standard 

fungicide treatment and untreated control. 

Figure 7. Suppression of sour rot on Vignoles grapes treated 

with UVC at 200 J/m2 compared to a standard fungicide 

treatment and untreated control. 

40 

12 

A 

Figure 8. The egg and 10 immature stages of 

mites are susceptible to UV treatments, and 

this technology is now widely 8 used, particularly 

in the Netherlands for suppression 

of mites in greenhouses and high tunnel 

6 

production systems. 


Continued from Page 2 41 

Both the 100 J/m 2 and 0 200 J/m 2 UVC 

treatments significantly but Untreated equivalently 

reduced the severity of powdery mildew 

on berries compared to the untreated 

vines, albeit not to the degree provided 

by the standard fungicide treatments 

(Figure 5, see page 41). What surprised 

us was that both the 100 J/m 2 and 200 J/ 

m 2 UV treatments also suppressed foliar 

downy mildew (Plasmopara viticola), 

and did so better than the fungicide 

standard (Figure 6). Laboratory studies 

indicated that the suppression of the 

4 

10 

Figure B 9. A tractor-drawn UVC lamp array used to treat grapevines at Cornell Agritech, and 

the same array carried by the autonomous robot Thorvald, manufactured by Saga Robotics. 

0 

Untreated 

C 

downy mildew pathogen was due to 

a pre-inoculation increase in host 

resistance. This was distinct from the 

Oxidate impact of UV on UVC powdery mildew, 

which was primarily a direct effect of 

UV on the pathogen itself. However, in 

our 2020 trials, weather conditions were 

especially conducive to downy mildew, 

and the level of suppression of downy 

mildew from UV was only around 50%. 

That’s helpful, but it is nowhere near 

acceptable commerical control. So, we 

obviously have more work to do in this 

area. 


30 

20 

The 2019 trials produced another 

surprise: the UV treatments effectively 

suppressed sour rot (Figure 7). This 

disease is a complex mess involving 

bacteria, fungi and fruit-feeding insects. 

We still don’t understand how UV is 

accomplishing this reduction, but given 

that there are very few effective means 

to suppress sour rot, any efficacy due to 

UV treatments is worth further investigation. 

In addition to suppressing plant pathogenic 

fungi, UV treatments can also 

suppress populations of phytophagous 

U 



40 

NAVEL ORANGEWORM MONITORING SYSTEMS 


30 

20 

10 

0 

Untreated UVC 

Fungicide 

Figure 10. Efficacy of UVC treatments for 

suppression of powdery mildew on Chardonnay 

grapes, 2020. 

mites (Figure 8). A number of studies 

have noted that UVB and UVC treatments 

can kill eggs of spider mites and 

European Red Mites. In addition to 

these effects, our preliminary trials indicate 

that the UV treatments can also 

alter behavior of adult mites, reduce egg 

laying, and reduce fecundity of the generation 

of surviving mites that emerge 

from UV treated eggs. 

As in our strawberry work, we eventually 

wanted to adapt the tractor-drawn 

grape UV array to a robotic carriage, 

and our partnership with SAGA robotics 

made this possible (Figure 9, see 

page 42). The navigation autonomy of 

the SAGA robot (Thorvald) is capable 

of tracking within a few centimeters of 

the trellis center at operational speeds 

between 1.25 to 2.5 mph. We evaluated 

UV doses between 100 J/m 2 and 200 J/ 

m 2 at frequencies of either once weekly 

or twice weekly. All of the evaluated 

doses significantly suppressed powdery 

mildew on both fruit and foliage, and 

the twice-weekly 200 J/m2 treatment 

provided control that was superior to 

the fungicide standard (Figure 10). 

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What’s Next? 

We are collaborating with growers and 

scientists at multiple locations in the 

U.S. and Europe, including Bully Hill 

Vineyards in Hammondsport, N.Y.; 

Washington State University’s research 

and extension center in Prosser, and 

the USDA Horticultural Crops Research 

Center in Corvallis, Ore. as 

well as multiple locations in California, 


— Brad Higbee, 

Field R&D Mgr, Trécé, Inc 

INCORPORAT ED 



trece.com 

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with designs and materials for UVC 

lamp arrays adapted for their vineyard 

pruning and training systems. These 

trials will be conducted over the course 

of the 2021 growing season. More 

about the autonomous robot Thorvald 

can be found at sagarobotics.com/. 

Our international working group 

is described on our project website: 

LightAndPlantHealth.org. It is a large, 

multidisciplinary, multi-institutional 

and international group representing 

several U.S. and overseas universities 

and government agencies, with industrial 

partnerships (Figure 11). 

The design of a lamp array to match a 

particular crop canopy and target pest 

biology is a critical aspect determining 

of the success of the treatments. Our 

cooperative projects with growers 

across the US have always involved our 

array designs and electronics. Some 

growers have designed and fabricated 

the various carriages for the arrays. 

But the UV array itself is NOT a DIY 

project, nor is calibration and the 

photobiological and epidemiological 

calculations that enter into calculations 

of a proper UV dose for specific applications. 

In addition to the engineering 

and biological considerations, both 

UVB and UVC can be injurious to you 

unless devices are properly designed 

and the lamps are properly shielded 

from direct view. No person should ever 

have an unshielded view of germicidal 

UV lamps, as there is a significant risk 

of eye and skin damage from exposure 

UVB and UVC. The protective gear that 

is required for safe applications is not 

expensive, and consists of UV-opaque 

clothing that covers all exposed skin, 

disposable gloves and a face-shield and 

eye protection rated for protection from 

UV. The arrays shown in this article 

also incorporate clear PVC curtains at 

each end of the array to limit escape 

of UV from the array. As would be the 

case with any IPM technology, UV does 

not pose undue risks to operators or the 

environment if used properly. Proper 

training and use protocols are the key 

to safe and effective applications. 

Figure 11. Group photo: Members of the research/extension team and advisory committee 

for our USDA-OREI project. Left to right: Laura Pedersen, Pedersen Farms, Geneva, NY; Eric 

Sideman, NOFA; Arupplillai Suthaparan, NMBU, Norway; Arne Stensvand, NIBIO Norway; 

Mariana Figueiro, Mount Sinai Light and Health Research Center (LHRC); Mark Rea, Mount 

Sinai LHRC; David Gadoury, Cornell University; Ole Myhrene, Myhrene AS, Norway; Rebecca 

Sideman, University of New Hampshire; and Robert Seem, Cornell University. Below (left to 

right), other members of the research and extension project team: Dr. Natalia Peres and PhD 

student Rodrigo Onofre, UFL Gulf Coast Research and Education Center; Dr. Lance Cadle-Davidson, 

USDA Grape Genetics Research Unit; Dr. Jan Nyrop, Department of Entomology, 

Cornell University and Director at Cornell AgriTech; Dr. Walt Mahaffee, USDA-ARS, Corvallis, 

OR; and Dr. Michelle Moyer, University of Washington, Irrigated Agriculture Research and 

Extension Center, Prosser. 

Our work has been funded by competitive 

grants from the USDA Organic Research 

and Extension Initiative, and the 

USDA Specialty Crops Research Initiative. 

Additional support has been provided 

by the National Research Council 

of Norway, the New York Farm Viability 

Institute, the USDA Sustainable 

Agriculture Research and Extension 

Program and Bully Hill Vineyards. We 

work as a diverse international group 

to promote this research area and its 

applications, and to act as a resource to 

train others. The work spans disciplines 

from plant growth and photobiology to 

physics and lighting technology. 

David M. Gadoury is a senior research 

associate in Cornell’s Plant Pathology 

and Plant-Microbe Biology Section at 

Cornell AgriTech, where his program 

focuses on pathogen ecology, pathogen 

biology and disease management. He 

leads the Light and Plant Health Group. 

References 

Gadoury, D.M., Pearson, R.C., Seem, R.C., Henick-Kling, 

T., Creasy, L.L., and Michaloski, A. 1992. Control of 

diseases of grapevine by short-wave ultraviolet 

light. Phytopathology 82:243. 

Janisiewicz, W. J., Takeda, F., Glenn, D. M., Camp, M. 

J., & Jurick, W. M. (2016a). Dark Period Following 

UV-C Treatment Enhances Killing of Botrytis cinerea 

3.Conidia and Controls Gray Mold of Strawberries. 

Phytopathology, 106(4), 386–394. https://doi. 

org/10.1094/PHYTO-09-15-0240-R 

Michaloski, A.J. 1991. Method and apparatus for 

ultraviolet treatment of plants. U.S. Patent no. 

5,040,329. 

Onofre, R. B., Gadoury, D. M., Stensvand, A., Bierman, 

A., Rea, M., and Peres, N. A. 2019. Use of ultraviolet 

light to suppress powdery mildew in strawberry 

fruit production fields. Plant Dis. 105:0000-0000 

(in press). 

Suthaparan, A., Stensvand, A., Solhaug, K. A., Torre, 

S., Mortensen, L. M., Gadoury, D. M., Seem, R. C., and 

Gislerød, H. R. 2012. Suppression of powdery mildew 

(Podosphaera pannosa) in greenhouse roses by brief 

exposure to supplemental UV-B radiation. Plant Dis. 

96:1653-1660. 

Suthaparan, A., Stensvand, A., Solhaug, K. A., Torre, S., 

Telfer, K. H., Ruud, A. K., Mortensen, L. M., Gadoury, D. 

M., Seem, R. C., and Gislerød, H. R. 2014. Suppression 

of cucumber powdery mildew by supplemental 

UV-B radiation in greenhouses can be augmented or 

reduced by background radiation quality. Plant Dis. 

98:1349-1357. 





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Irrigation Scheduling In 

Winegrape Vineyards 

Combine technology tools to confirm grapevine water needs. 

BY CRAIG MACMILLAN | Niner Wine Estates 

and KRIS BEAL | Vineyard Team 

The vine’s response to irrigation depends on soil physics, changes in weather patterns year to year, vine age, crop load, canopy size and 

disease status (photo courtesy C. Macmillan.) 

Irrigation is probably the most powerful 

tool a winegrape grower has in 

their tool box. Intelligent use of irrigation 

can control canopy size, manage vine 

stress, manipulate berry size, improve 

wine quality and conserve water. The key 

to achieving a grower’s viticultural goals 

through irrigation is data-driven scheduling 

to determine when and how much to 

irrigate. 

The tools growers have available for 

irrigation scheduling generally fall into 

five categories: soil-based, plant-based, 

weather-based, remote sensing and visual 

assessment of the vine’s water status. 

Soil-Based Methods and Technologies 

Soil moisture sensors are an effective way 

of measuring how much water is in the 

soil, where it is in the profile and how 

and when the vine is taking up that water. 

Another benefit of soil moisture sensors is 

the ability to measure the effect of winter 

rain on the soil profile 

For the best resolution, multiple sensors 

are needed per block reflecting soil types 

and topography. The key is placing sensors 

in locations which are representative 

of larger areas. Soil maps can help identify 

the best locations. Ideally, a soil map 

was made prior to vineyard installation. 

Mapping can still be done after installation 

with the help of a professional agricultural 

soils expert. Identifying representative 

areas within a vineyard can also 

be done using Normalized Difference 

Vegetative Index (NDVI) mapping. These 

maps identify areas of weak or excessive 

vigor. Those areas should be avoided as 

locations for sensors. 

The best depths for sensor placement can 

be determined by taking soil cores with 

a hand auger. Look for changes between 

soil horizons which might impact water 

holding capacity. Depths should represent 

rooting depths and just below 

to monitor deep percolation. Place the 

sensor in the vine row approximately 18 

inches from the vine trunk and four to 

six inches from the emitter. 

Types of soil moisture sensors include 

quantitative technologies such as time 

domain transmissometry, capacitance 

measurements, time domain reflectometry 

and qualitative methods such as 

matric potential. Each has its advantages 

and disadvantages in terms of cost, soil 

volume measured and ease of installation. 

No one type of sensor is ideal for all 

situations, so some research and ground 

truthing against other methods like visual 

assessment is required to find the best 

fit for your particular vineyard. 

Plant-Based Methods 

and Technologies 

Probably the most common method for 

evaluating vine water status is leaf or 

stem water potential using a device such 

as a pressure bomb. This method measures 

the tension (or “potential”) between 

the pull of water through the plant from 

evapotranspiration and how tightly water 

is held to the soil. A leaf is cut from the 

vine. The blade is placed under pressure 

forcing water back through the xylem of 

the petiole. The more pressure required to 

force the water out, the drier the vine is. 

A porometer is another tool which directly 

measures an indicator of vine water 

status. Porometers provide a reading of 

how relatively open or closed the stomata 

are on the leaf. Stomata are open when 

there is water available for evapotranspiration. 

When stomata start to close, 

the vine is protecting itself from drying 

out—a sign of stress. A sensor is clipped 

to a leaf blade and a measurement is taken 

automatically. 

An indirect measurement of stomatal 



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Register at progressivecrop.com/conference 

closure can be done with an Infrared 

thermometer. Transpiration cools the 

surface of the leaf, making it cooler 

than the ambient air temperature. As 

stomata close, the temperature of the 

leaf blade increases. Readings are taken 

by simply pointing an infrared thermometer 

at the canopy. This method is 

simple, quick and generates good quality 

data that is easy to interpret when 

analyzed over time. 

Weather-Based Methods 

and Technologies 

While not a direct measure of vine 

water status, weather-based methods 

allow for data-informed scheduling 

decisions for the vineyard as a whole. 

By estimating how much water vines 

have transpired, a grower can decide 

how much water to put back into the 

soil, or not, in the case of deficit irrigation. 

This is done by estimating the 

daily water loss of the vine using evapotranspiration 

(ET) rates. The baseline 

for comparison is the reference ET, also 

called ET O 

or “full ET”. The California 

Irrigation Management Information 

System (CIMIS) maintains remote stations 

throughout California to provide 

reliable estimates of ET. Many weather 

stations available today also estimate 

ET O 

. 

Grapevines do not transpire at the full 

ET rate, so a crop coefficient (K C 

) is 

required to better reflect how the vine 

is behaving under these conditions. 

Essentially, the more canopy, the more 

water is transpired by the vine. As 

canopy size varies during the course of 

the growing season, the ratio of water 

transpired by the vine to reference ET 

changes. Therefore, the crop coefficient 

needs to be calculated at multiple times 

during the season. Calculating the crop 

ET (ET C 

) uses the equation ET O 

× K C 

= 

ET C 

. 

K C 

is determined by measuring the 

percent of the vineyard floor shaded 

at solar noon. This can be done with a 

gridded board to estimate the width of 

the shade and the percent of gaps in the 

shaded area. The percentage of shaded 

floor area is then used in the following 

equation to calculate the crop coefficient: 

K C 

= Percent shaded area × 0.017 

Using ET C 

is especially helpful for 

successful deficit irrigation. A crop 

coefficient for deficit irrigations, called 

K RDI 

, can be calculated by multiplying 

K C 

by the percent deficit desired using 

the equation K C 

× %RDI target = K RDI 

. 

This gives the grower confidence that 

they are hitting their specific target for 

deficit irrigation taking current weather 

conditions into account. 

An example: 

The percent of vineyard floor shaded is 

25%. 

This gives a K C 

of 0.425. 

If the RDI target is 75% the K RDI 

is 0.319. 

If the ET O 

rate for the week is two inches, 

0.638 acre-inches should be applied 

to maintain vines at their current water 

status. 

Remote Sensing 

Remote sensing using the Normalized 

Difference Vegetative Index (NDVI) is 

a powerful tool as it provides a literal 

picture of vine vigor across a large area 

to a high degree of resolution. Maps are 

created by flying over the vineyard with 

a drone or fixed wing aircraft. Cameras 

on the aircraft record the amounts 

of near infrared and red wave lengths 

reflected by the vineyard canopy. 

NDVI is calculated using an equation 

that compares these wavelengths. The 

resulting numbers correlate to the 

relative photosynthetic activity of the 

canopy which is directly tied to vine 

water status. 

Visual Assessment 

Purely qualitative practices for assessing 

vine water status are commonly 

used by growers. One can simply look 

at the appearance of vines searching for 

tell-tale signs of stress without the need 

for any devices. This is an excellent way 

of ground truthing other methods. 

Vine response to stress can readily be 

seen in the growth pattern of shoots 

and angle of leaf blades. When tendrils 

extend far beyond the shoot tip, the 

vine is growing rapidly and is under no 

stress. As the soil and vine begin to dry 

out, tendrils become shorter. 

Shoot tips are another good indicator. 

The state of a shoot tip can be determined 

by folding the last fully opened 

leaf up toward the tip. If the shoot tip 

extends past the leaves, it is active. If 

the folded leaves cover the shoot tip, it 

has stopped growing. Eventually, the 

tip will die altogether. 

Leaves provide another clue to vine 

stress. Under stress, leaves begin to 

droop. Leaves on an unstressed vine 

will form an obtuse angle to the petiole. 

As stress progresses, this angle becomes 

less and less until it is acute. 

Using visual inspection of the vine 

successfully requires many years of 

experience to perfect. Combining experience 

with quantifying technology 

may give the grower more confidence 

that their “read” of the vines is correct. 

One serious drawback of relying solely 

on looking at vines for indicators of 

stress is that there is a delay between 

the onset of stress and the symptoms 

becoming apparent in the state of the 

canopy. Overshooting a stress goal under 

RDI can be difficult to recover from, 

especially during late season. 

Consider using a combination of at 

least two different types of irrigation 

scheduling methods as each measures 

different variables and provides a different 

viewpoint of what is happening 

in the field. The vine’s response to irrigation 

depends on soil physics, changes 

in weather patterns year to year, vine 

age, crop load, canopy size and disease 

status. Taking all those variables into 

account is challenging even with the 

best tools. The more tools in the tool 

box, the better equipped the grower is 

to harness the power of well scheduled 

irrigation. 






Grapevine Trunk 

Diseases 

Research Updates for 

Pruning Wound Protection 

Strategies 

A 

By ROBERT BLUNDELL | Robert Blundell, Graduate Student Researcher, 

UC Davis 

AKIF ESKALEN | Plant Pathologist, UCCE Specialist, UC Davis 

Grapevine trunk diseases (GTDs) 

are currently considered one of 

the most important challenges for 

viticulture worldwide. These widespread 

damaging diseases are caused by a 

broad range of permanent, wood-colonizing 

fungal pathogens, which 

primarily gain entry into grapevines 

via pruning wounds. GTDs can also 

reside latently within tissue as part of 

the normal grapevine microbiota, and 

environmental factors may trigger their 

switch to pathogenic. 

The economic impact of GTDs can be 

significant in both young and mature 

vines, with Black foot disease and Petri 

disease being predominant in young 

vines. In mature vines, Esca (Figure 1), 

Botryosphaeria dieback (Figure 2a and 

2b, see page 49), Eutypa dieback (Fig. 

2c and 2d, see page 49) and Phomopsis 

dieback are damaging and referred to 

as canker diseases due to characteristic 

cankers they cause in vines. Other 

major symptoms of their presence 

include poor vigor, leaf chlorosis (Fig. 

1a), berry specks and shoot and tendril 

dieback. Perennial cankers cause spur, 

cordon and trunk dieback and ultimately 

result in death of the entire vine. 

The majority of the fungal pathogens 

responsible for GTDs produce overwintering 

fruiting structures containing 

the infectious spores of the pathogen. 

These overwintering structures 

can be found on the bark surface of 

infected vines as well as on pruning 

and harvesting debris on vineyard 

floors. Another source of GTD fungal 

inoculum (spores) is from other woody 

perennial crops such as nut trees which 

are known to be infected by GTDs. 

Under conducive environmental 

conditions, largely precipitation events, 

the fruiting bodies release fungal 

spores which land on exposed pruning 

wounds, causing infection and thus 

completing their life cycle. Research 

has identified that the majority of spore 

release in California occurs during 

winter following precipitation (December 

to February), which also overlaps 

with pruning timing, thus creating 

a window for GTDs to infect vines. 

With this knowledge, pruning wound 

protection strategies alongside cultural 

practices are the best strategies to 

mitigate GTDs. Cultural practices are 

focused around sanitation, including 

using clean material when establishing 

a new vineyard, removal of pruned 

and infected material and pruning 

dead shoots, spurs and cordons below 

symptomatic tissue. Delayed pruning 

after the high disease pressure period 

has passed is another good option in 

California to mitigate GTD infection. 

The most effective way to protect 

pruning wounds from airborne fungal 

spores of GTDs is to apply registered 

chemical and/or biological pruning 

wound protectants. Ideally, these protectants 

should be applied shortly after 

pruning and in a dry weather window 

to avoid rain washing the solution away. 

B 

C 

Figure 1. Symptoms of esca vine decline: 

a) classic leaf stripe symptoms of esca; 

b) cross-section showing central white 

rot and canker on esca infected vine; and 

c) black spot and sectorial necrosis of 

esca-infected vine. 


A 

C 

B 

D 


Methodology 

This comprehensive study was performed 

to evaluate a variety of registered 

and experimental chemical and 

biological agents to protect pruning 

wounds (Table 1) from the fungal 

pathogens Neofusicoccum parvum and 

Eutypa lata, which are aggressive causal 

agents of the GTDs Botryosphaeria 

dieback and Eutypa dieback, respectively. 

This study was set up in both a 

wine grape and table grape commercial 

vineyard in Sacramento County (cv 

Cabernet Sauvignon) and Kern County 

(cv Allison), respectively. 

Figure 2. Symptoms of grapevine trunk diseases on mature vines: a) classic dead arm 

symptoms of Botryosphaeria dieback disease; b) wedge-shaped canker characteristic of 

Botryosphaeria dieback; c) Eutypa dieback include stunted shoots with necrotic leaves; and d) 

canker and internal necrotic wedge-shaped staining in cross section of cordon characteristic of 

Eutypa dieback. 

The damaging effects of GTDs on vineyard 

longevity are likely to be reduced 

significantly if protectants are adopted 

when vines are young and subsequently 

applied annually. 

Commercial chemical protectants such 

as a combination of Rally and Topsin M 

have been shown to be effective in controlling 

GTDs. With a need for sustainable 

alternatives, there is huge interest 

in the research, development and use of 

biological pruning wound protectants. 

Biological pruning wound protectants 

exploit beneficial micro-organisms 

that possess either natural antagonistic 

activity or compete with the pathogen 

by colonizing the pruning wound faster 

to provide protection from GTD pathogens. 

Several commercially available 

beneficial microorganisms, including 

Trichoderma spp. and Bacillus spp., 

have been shown to provide protection 

against GTDs (Brown et al. 2020; Kotze 

et al. 2011; Halleen et al. 2010; John 

et al. 2008). As well as being an alternative 

to fungicides, it is thought that 

biologicals could provide prolonged 

protection once they have colonized the 

pruning wound. 

All study vines were pruned (one foot 

long) in February (Figure 3a, see page 

50), and within 24 hours of pruning, 

the liquid protectants were sprayed 

with a one-liter hand-held spray 

bottle on the pruning wound until 

runoff (Figure 3b, see page 50). All 

protectants were prepared according 

to their label recommendations. The 

following day, canes treated with a 

chemical protectant were inoculated 

with roughly 2000 spores of either N. 

parvum or E. lata. Canes treated with 

a biological protectant were inoculated 

with the same amount of spores of 

either N. parvum or E. lata seven days 

after treatment application (Figure 

3c, see page 50). The positive control 

treatment had sterile distilled water 

applied to wounds and was inoculated 

with the same amount of spores 

of each pathogen. Eight months after 


Treatment or Trade Name Active Ingredient Manufacturer 

Application rate 

per acre (100gal) 

Table 1. List of all treatments used in the study, including their active ingredient, manufacturer and application rate. 



pathogen that was inoculated (Figure 

3e). After incubation for 5 to 14 days at 

room temperature, recovery of fungal 

pathogens was recorded by their morphological 

characteristics. The efficacy 

of the treatments controlling the GTDs 

was calculated as the Mean Percent of 

Infection (MPI) using the following 

formula: Number of GTD-infected 

samples (canes from which the pathogen 

could be re-isolated)/total number 

of canes inoculated x 100. 

Figure 3. a) Spur pruning of vines in February 2020: b) application of protectants; c) inoculation 

of pruned canes with GTDs; d) treated canes split longitudinally; and e) isolated segments 

cultured on growth media. 


inoculation, treated canes were collected 

and brought to the lab for further 

evaluation. Each cane was split with a 

knife longitudinally (Figure 3d) and 

segments were excised and plated 

on a growth medium to confirm the 

Results 

Our results from both field studies show 

that Biotam, a Trichoderma-based biological 

product, was the superior protectant 

overall, providing a consistently 

high level of pruning wound protection 

compared to the water-treated, inoculated 

positive control. In the Sacramento 

County trial, Biotam application 

resulted in an MPI of 5% and 0% for E. 

lata and N. parvum, respectively, compared 

to the water-treated, inoculated 

positive control with an MPI of 40% 

and 70% for E. lata and N. parvum, respectively 

(Figure. 4a and 4b). In Kern 

County, Biotam application resulted in 

an MPI of 0% and 10% for E. lata and 

N. parvum, respectively, compared to 

Mean Percent Infection of 

E. Lata (MPI)% 


N. parvum (MPI)% 

50 

40 

30 

20 

10 

0 

80 

60 

40 

20 

0 

Biotam 

Botector 

Topsin M + Rally 

Water treated - Non 

inoculated negative control 

Biotam 

Vintec 

BioTam + Crab Life-Powder 

GCM 

Sacramento County 

UCD 8745 

Vintec 

UCD 8189 




UCD 8189 

Luna Sensation 

Serenade 

UCD 8717 

Botector 

Serenade 

GCM 

Terramera (Exp B) 


Crab Powder 

UCD 8717 

Water treated - Inoculated 

positive control 

UCD 8745 

UCD 8189 

Crab Life Powder 






E. Lata (MPI)% 


N. parvum (MPI)% 

30 

25 

20 

15 

10 

5 

0 

Biotam 


50 

40 

30 

20 

10 

0 

Serenade 

Vintec 

Biotam 




Kern County 

Vintec 

UCD 8717 

GCM 



Serenade 

UCD 8189 

UCD 8745 


Bacillus veleze fermented product 

Botector 





Botector 




UCD 8745 


UCD 8717 


UCD 8189 



Figure 4. Evaluation of treatments for pruning wound protection 

of E. lata (a) and N. parvum (b) in Sacramento County. 

Figure 5. Evaluation of treatments for pruning wound protection of 

E. lata (a) and N. parvum (b) in Kern County. 



the water-treated, inoculated positive 

control with an MPI of 25% and 45% 

for E. lata and N. parvum, respectively 

(Figure 5a and 5b, see page 50). This 

shows that Biotam is capable of providing 

simultaneous pruning wound 

protection against multiple fungal 

pathogens of GTDs, which is often 

challenging for protectants to achieve. 

Another Trichoderma-based biological 

product, Vintec, was also effective 

at protecting wounds. Application of 

Vintec (2.8 oz/A) resulted in an MPI of 

15% and 5% for E. lata and N. parvum, 

respectively, in Sacramento County 

(Figure 4a and 4b, see page 50) and an 

MPI of 5% and 10% for E. lata and N. 

parvum, respectively, in Kern County 

(Figure 5a and 5b, see page 50). 

Our results also showed that the chemical 

protectants Topsin M + Rally and 

Luna Sensation were effective at providing 

simultaneous pruning wound 

protection of E. lata and N. parvum 

in both Sacramento and Kern County 

trials. Application of Topsin M + Rally 

resulted in an MPI of 10% for both 

E. lata and N. parvum in Sacramento 

County (Fig. 4a and 4b, see page 50) 

and an MPI of 5% and 10% for E. lata 

and N. parvum, respectively, in Kern 

County (Figure 5a and 5b, see page 

50). Several naturally occurring biocontrol 

agents, including Trichoderma 

hamatum (UCD 8717), Aureobasidium 

pullulans (UCD 8189) and Bacillus 

sp. (UCD 8745), that were identified 

in California vineyards were also 

performing very well compared with 

other commercially available products 

(Figure 4 and 5, see page 50). 

Baumgartner, K. 2021. Pruning-wound 

protectants for trunk-disease management 

in California table grapes. Crop 

Protection, 141. 

Halleen, F., Fourie, P.H., and Lombard, 

P.J. 2010. Protection of grapevine 

pruning wounds against Eutypa lata 

by biological and chemical methods. A. 

Afr. J. Enol. Vitic. 31: 125–132. 

Kotze, C., Van Niekerk, J., Mostert, 

L., Halleen, F., and Fourie, P. 2011. 

Evaluation of biocontrol agents for 

® 

grapevine pruning wound protection 

against trunk pathogen infection. Phytopathol. 

Mediterr. 50: 247–263. 

John, S., Wicks, T.J., Hunt, J.S., and 

Scott, E.S. 2008. Colonisation of 

grapevine wood by Trichoderma harzianum 

and Eutypa lata. Aust. J. Grape 

Wine Res. 14:18-24. 


to hear from you. Feel free to email us 

at article@jcsmarketinginc.com 

The Grower’s Advantage 

Since 1982 

Effective Plant Nutrients and Biopesticides 

to Improve Crop Quality & Yield 

© 

In conclusion, our 2020 field trials 

have shown that several biological and 

chemical treatments can provide efficient 

protection of pruning wounds of 

grapevine against one or more fungal 

pathogens responsible for the major 

grapevine trunk diseases (Esca, Botryosphaeria 

dieback and Eutypa dieback). 

Moreover, improving accurate 

diagnosis of GTDs will be essential in 

determining an effective product. 

ORGANIC 

Contains Auxiliary Soil & Plant Substances 

Botector ® 

Biofungicide 

® 

ORGANIC 

Plant Nutrients & Adjuvants 

® 

GARGOIL 

INSECT, MITE & DISEASE CONTROL 

Blossom Protect 

Biopesticide 

® 

Herbicide EC 

® 

References 

Brown, A.A., Travadon, R., Lawrence 

D.P., Torres, G., Zhuang., and 

For more information, call (800) 876-2767 or visit www.westbridge.com 


® 

IMAGINATION 

INNOVATION 

SCIENCE IN ACTION

Progressive Crop Consultant May/June 2021

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