September/October 2017

September/October 2017 

The Pressure Chamber 

Does it Have a Place in Your Toolbox? 

Pythium Wilt Disease of Lettuce causing 

Diagnostic Challenge 

Remote Sensors for Precision Ag at West Hills College 

California Pistachio Salt Tolerance Update 

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PUBLICATION 

Volume 2 : Issue 5

PUBLISHER: Jason Scott 

Email: jason@jcsmarketinginc.com 

EDITOR: Kathy Coatney 

Email: article@jcsmarketinginc.com 

PRODUCTION: design@jcsmarketinginc.com 

Phone: 559.352.4456 

Fax: 559.472.3113 

Web: www.progressivecrop.com 

CONTRIBUTING WRITERS & INDUSTRY SUPPORT 

Terry Brase 

Precision Ag Instructor, 

West Hills College 

Richard Buchner 

UCCE Orchard Advisor for 

Tehama County, Emeritus 

Louise Ferguson 

Pomology Extension 

Specialist, Department of 

Plant Sciences 

Allan Fulton 

UCCE Irrigation and Water 

Resources Advisor 

Craig E. Kallsen 

Farm Advisor, 

UCCE Kern County 

Steven T. Koike 

UCCE, Plant Pathology 

Advisor, Monterey County 

Luke Milliron 

UCCE Orchard Systems 

Specialist 

Butte, Glenn and Tehama 

Counties 

Blake L. Sanden 

Farm Advisor, 


Mike Stanghellini 

Director of Research & 

Regulatory Affairs, TriCal 

Inc., Hollister, CA 

Andreas Westphal 

Nematology, UC Riverside, 

Kearney Agricultural 

Research and Extension 

center, Parlier, CA 

Amy Wolfe 

MPPA, CFRE 

President & CEO, AgSafe 

4 

12 

16 

IN THIS ISSUE 

The Pressure Chamber – 

Does it Have a Place in Your Toolbox? 

Pythium Wilt Disease of Lettuce 

causing Diagnostic Challenge 

Fumigation Alternatives for Tree 

and Vine Crops 

Are There Novel Materials for Soil Fumigation? 

22 Pesticide Safety in the Orchard 

UC Cooperative Extension Advisory Board 

Kevin Day 

County Director and 

UCCE Pomology Farm 

Advisor, Tulare/Kings County 

Steven Koike 

UCCE Plant Pathology 

Farm Advisor, Monterey & 

Santa Cruz Counties 

24 

California Pistachio Salt Tolerance 

Update 

David Doll 

UCCE Farm Advisor, Merced 

County 

Dr. Brent Holtz 

County Director and UCCE 

Pomology Farm Advisor, San 

Joaquin County 

Emily J. Symmes 

UCCE IPM Advisor, 

Sacramento Valley 

Kris Tollerup 

UCCE Integrated Pest 

Management Advisor, 

Parlier, CA 

28 

Remote Sensors for Precision Ag at 

West Hills College 

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. 

2 Progressive Crop Consultant September/October 2017

4 

UPCOMING EVENTS: 

South Valley Nut Conference 

October 27, 7:00AM - 1:30PM - wcngg.com 

Tulare County Fairgrounds - Tulare, CA 

Come out for a day of free food, giveaways, and industry 

networking. 

CE Credits offered: CCA: 4 Hours | PCA: 3 Hours 

Mid-Valley Nut Conference 

November 3, 7:00AM - 1:30PM - wcngg.com 

Modesto Jr. College West Campus, ACE Ag Pavilion - Modesto, CA 

Enjoy experiencing our trade show in the heart of the Central 

Valley. A scholarship will be given to the Modesto Jr. College 

ag program. 

CE Credits offered: CCA: 4 Hours | PCA: 2.5 Hours 

12 

24 

16 

22 

28 


www.progressivecrop.com 

3

The Pressure Chamber – 

Does It Have a Place in 

Your Tool Box? 

By: Allan Fulton, Luke Milliron, and Richard Buchner 

Among the most basic observations that can be 

used to manage irrigation in orchard crops are 

visual cues of crop water stress. However, these cues 

can be somewhat subjective and are often expressed 

after plant stress is higher than desired. Measuring 

midday stem water potential (SWP) using a pressure 

chamber is a quantitative method for evaluating 

plant water status, and relationships have been established 

between pressure chamber measurements and 

tree growth and productivity. From these relationships, 

guidelines have been developed to assist growers 

in making irrigation scheduling decisions. 

This is an abbreviated discussion of pressure 

chamber operation and interpretation of measurements 

based upon peer-reviewed UC ANR Publication 

8503, Using the Pressure Chamber for Irrigation 

Management in Walnut, Almond, and Prune (2014). 

Plant Water Status 

During plant transpiration, water moves from 

the soil into fine root tips, up through the vascular 

system, and out into the atmosphere (fig.1). 

Water flows through the tree from high potential 

in the soil (about –0.1 bar) to low potential in the 

Figure 1. Illustration of how water moves from the soil through an irrigated 

tree and into the atmosphere, from both a whole-tree and cellular perspective. 

SWP measures the water potential gradient that drives this movement of water 

through the tree. Source: Adapted from Pearson 2008. Upper Saddle River, 

NJ: Pearson Education Inc. 


atmosphere (less than –40 bars). 

Low potential is created at the leaf 

surface through small openings 

called stomata that open and close 

to regulate photosynthesis, gas 

exchange, and plant water loss. 

Simultaneously, water held in the 

soil enters root tissue and begins its 

journey to the leaves. This creates a 

vacuum, or continuous column of 

tension within the water-conducting 

system of the tree. The amount 

of tension depends on the balance 

between available soil moisture and 

the rate at which water is transpired 

from leaves. 

Midday Stem Water 

Potential (SWP) 

Concept 

A pressure chamber measures 

plant water tension by applying 

pressure to a severed leaf and stem 

enclosed in an airtight chamber 

(fig. 2). The sample leaf is covered 

with a foil-laminate bag for at least 

ten minutes before it excised from 

the tree. The leaf remains in the bag 

while the measurement is taken. 

requiring more pressure to force 

water out of the cut surface of 

the leaf stem. 

Stem water potential is a 

direct measure of water tension 

(negative pressure) within the 

plant and is given in metric units 

of pressure, such as bars (1 bar is 

about 1 atmosphere of pressure, 

or 14.5 psi). Technically, SWP 

should always be shown as a 

negative value (e.g., –10 bars), 

but in conversation and because 

the gauge does not indicate 

negative values, we often omit 

mentioning “negative” before the 

value. A larger number on the 

gauge indicates more tree water 

stress. 

Figure 3. Four examples of commercially available pressure chambers. Example A is a 

pump-up style by PMS Instruments in which a foot pump creates air pressure in the rectangular 

chamber. Example B, by Specialty Engineering, also has a rectangular chamber, 

employs a tripod to hold the pressure chamber, and uses compressed carbon dioxide (CO2) 

gas to supply the pressure. Example C is a suitcase-style pressure chamber. It has a cylindrical 

chamber that uses nitrogen gas, to pressurize the chamber. Both PMS Instruments and 

Soilmoisture Equipment Corp. offer this style of pressure chamber. Example D is a consoleor 

bench-style pressure chamber by Soilmoisture Equipment Corp. that also uses nitrogen 

gas to pressurize the chamber. Photos: Courtesy of Plant Moisture Stress (PMS) Instrument 

Company, Albany, OR (A, C); Specialty Engineering, Waterford, CA (B); and Soilmoisture 

Equipment Corp., Santa Barbara, CA (D). 

A 

C 

B 

D 

bers for measuring stem water potential (SWP). 

All have the same basic components and operate 

on the same concept. The choice of a pressure 

chamber depends largely on preferences. Several 

pressure chamber styles and designs are available, 

ranging from simple manual pump-ups to consoles 

with more advanced features (fig. 3). Compressed 

nitrogen gas is a convenient, relatively inexpensive, 

and inert (safe) gas to use as a source of pressure. 

Carbon dioxide gas is also used to supply pressure 

with some pressure chambers. Compressed air is 

used with some pressure chamber models. The cost 

may range from about $1,000 to about $7,000, depending 

on the style, design, and whether the unit 

is new or used. 

Figure 2. Schematic showing how water potential is measured in a severed 

leaf and stem (petiole) using a hand-held pump-up pressure chamber. Source: 

Adapted from Plant Moisture Stress (PMS) Instrument Company. 

The pressure required to force 

water out of the stem of a severed 

leaf equals the water potential and 

is measured by a pressure gauge. 

As soil moisture is depleted, more 

tension develops in the plant, 

Pressure Chamber 

Selection 

A number of companies produce 

durable, portable, and relatively 

inexpensive pressure cham- 

Costs to Monitor Plant 

Water Status 

Growers and consultants who already use the 

pressure chamber and midday stem water potential 

as one of their management tools indicate the 

cost to integrate it into their management ranges 

from about $10 to $20 per acre annually. This is a 

Continued on Page 6 



5

Continued from Page 5 

relatively low cost compared to the cost 

of water and other production practices. 

This accounts for the labor to take 

the measurements, compressed gas 

(nitrogen or carbon dioxide), time to 

evaluate the data, and maintenance of 

the instrument. It does not reflect the 

cost of purchasing the pressure chamber. 

Pressure chambers are generally durable 

if handled and maintained reasonably. 

It’s not uncommon for a pressure chamber 

to last many years, so the cost of the 

instrument is generally nominal when 

amortized over several years and many 

acres. 

Making Stem Water 

Potential Measurements 

Time of Day 

Stem water potential (SWP) is best 

measured midday from 12:00 to 4:00 

p.m. The idea is to make measurements 

when the tree is experiencing relatively 

constant and maximum water demand. 

From a practical standpoint, irrigation 

managers are interested in the highest 

stress that trees experience, which is also 

at midday. Thus, the guidelines for interpreting 

SWP measurements have been 

made by using midday measurements. 

Time of Season 

SWP measurements should begin 

during the spring and continue through 

the summer and fall. This approach will 

help indicate when to apply the first irrigation, 

show how orchard water status 

responds to irrigation decisions, how 

irrigation scheduling might be improved 

and how water status shifts with seasonal 

weather changes. Postponing SWP measurements 

until early summer will miss 

the progressive changes in orchard water 

status leading up to the summer season 

(when water demand is highest). 

Time Between Irrigations 

PMS Instrument Company 

Plant Based Irrigation Scheduling 

Orchard acreage, time availability, 

coordination with other tasks, previous 

experience, and specific interests (troubleshooting) 

may influence measurement 

frequency. Not all orchards have 

to be measured at the same frequency. 

Measuring SWP just prior to irrigation 

and one or two days after irrigation 

provides the most information about 

the ongoing water status of the orchard. 

SWP measurements taken just before 

irrigation will indicate the orchard water 

status when orchard stress is potentially 

the highest, and provide insight into 

whether the interval between irrigations 

needs to be adjusted. Monitoring SWP 

one or two days after irrigation will indicate 

how well the tree water status recovered 

after irrigation and give insight 

into whether the duration of irrigation is 

on track. 

Larger changes in SWP may be observed 

before and after irrigation when 

irrigation frequency is stretched out 

more with a flood or sprinkler system 

that applies more water in a single irrigation. 

Conversely, smaller, more gradual 

changes in SWP may be observed with 

drip and microsprinkler systems that 

apply water at higher frequency and 

lower volume. So, it is not necessary or 

usually feasible to measure SWP before 

and after every drip or microsprinkler 

irrigation. Measuring SWP just before a 

drip or microsprinkler irrigation every 

seven to 10 days should provide reasonable 

trends and insights into the orchard 

water status. 

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How many measurements to make 

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Determining how many trees to 

monitor must balance having enough 

trees to reliably represent the orchard 

and being able to cover the desired total 

acreage in a timely and efficient manner. 

Sampling fewer trees and accepting 

the possibility of less-representative 

measurements is better than not using 

SWP at all because it is perceived as too 

labor intensive. The number of trees to 

monitor in an orchard also depends on 

soil variability and irrigation uniformity. 

Fewer trees are needed if the orchard is 

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are needed if there is more than one 

soil type and non-uniform irrigation. A 

sampling strategy that can be completed 

in about 30 to 60 minutes per orchard is 

ideal, especially if several orchards must 

be monitored on the same afternoon. 

Understanding of orchard water status 

will improve as the number of trees 

monitored is increased. A sample size 

ranging from 5 to 10 trees per orchard is 

probably optimal for achieving representative 

measurements and covering acreage 

efficiently. One strategy is to start 

with a greater number of measurement 

trees and then pare down over time, as 

the trends and patterns of orchard water 

status is more understood. 

Selecting trees for measurement 

Trees selected for SWP monitoring 

should be representative of the orchard. 

Good measurement trees would be of 

the same variety and rootstock and similar 

in age, degree of pruning, and canopy 

size. Measurement trees should be 

irrigated in the same manner as the rest 

of the orchard and should be healthy. 

The trees selected for SWP measurement 

should be at least 100 feet inside 

the orchard and have other healthy trees 

growing around them. The same trees 

should be used to measure SWP each 

time to reduce variation from one day 

to the next. The sample trees should be 

marked with flagging, spray paint, GPS 

waypoints (or a combination thereof), 

so they are easily located each time SWP 

measurements are made. Going back to 

the same trees for each reading, reduces 

variability and may be more important 

than the number of trees measured. 

When sampling small trees, particularly 

during the first year, excessive leaf 

removal may be an issue, especially if the 

trees are planted later and not growing 

vigorously. One solution is to identify 

three or four side-by-side rows of uniformly 

growing trees in representative 

areas of an orchard. Each row will have 

three or four trees identified for SWP 

measurement. Then, using a rotational 

schedule, measure SWP in a different 

row each reading, returning to the first 

row after trees have had time to grow 

additional leaves suitable for measurement 

(usually two or three weeks after 

the previous measurement). Typically, 

second-year and older trees should have 

sufficient canopy, that rotating between 

rows of sample trees is no longer necessary. 

How many leaves per tree? 

To ensure the reading is not compromised 

by operator error or poor 

leaf selection, it is important to make 

two measurements per tree, or a single 

leaf from two adjacent trees. Compare 

the readings; if they are more than 0.5 

Figure 4. From left to right, healthy full grown leaves are selected in the lower interior canopy 

of an almond, prune, and walnut tree near larger branches of the trunk and covered 

with mylar foil bags for at least ten minutes. Walnut has a compound leaf, so the terminal 

leaflet is selected because it has a longer petiole which assists the measurement. (Photos: 

A. Fulton) 

to 1.0 bar apart, another leaf should be 

measured and the average of the closest 

leaves recorded. If the difference 

between the two leaves is great, bag 

another leaf and return to make the 

measurement. Then, take the average of 

the closest measurements. An alternative 

strategy is to bag three leaves per tree 

then measure the first two, and if the 

measured SWP is in good agreement 

pass on the third measurement. 

Good SWP field measurement 

technique 

Consistent technique helps improve 

the accuracy of SWP measurements. 

On the same almond trees, as much as 

a 2-bar discrepancy, plus or minus, has 

been documented with different operators. 

Such errors can be due to differences 

in speed and method of handling the 

sample from the time the leaf is excised 

until the measurement is completed, or 

they can be due to differences among 

operators in recognizing the endpoint. 

Relying on one operator to check the 

same orchards over the season, using the 

same pressure chamber and consistent 

technique is recommended. 

Good SWP measurement technique 

begins with properly selecting sample 

leaves and bagging or covering them 

with a foil-laminate bag (fig. 4). Leaves 

should be healthy, full grown, and without 

apparent nutritional deficiencies, 

yellowing from excessive shading or 

older age, or physical damage from wind 

or hail. Lower interior, shaded leaves 

are selected nearer to larger branches 

of the tree trunk, where the bagged leaf 

equilibrates readily with the tree’s main 

water-conducting system. Leaves higher 

in the canopy or farther out on a limb 

can give significantly different levels of 

SWP due to more resistance to water 

flow through more of the vascular system. 

Reflective, water-impervious mylar 

foil bags are commonly used for bagging 

leaves. Bags are available from some 

pressure chamber manufacturers. Nylon 

button fasteners, re-sealable zip fasteners, 

paper clips, clothes pins and other 

creative approaches can be used to fasten 

the foil bags to the leaves. 


The importance of bagging or covering 

the sample leaves on large perennial 

trees can’t be emphasized enough. 

Ideally, the sample leaves are bagged for 

at least 10 minutes prior to excising the 

leaf from the tree. It is acceptable to bag 

leaves longer than 10 minutes. They may 

be covered several hours or even a day in 

advance if it adds convenience. 

After the trees with the sample leaves 

have been bagged for at least 10 minutes, 

it is time to measure the SWP with a 

pressure chamber. The leaf must remain 

enclosed in the bag after it is excised 

from the tree and placed in the chamber. 

If the bag is removed at any time, the 

SWP level will begin to change rapidly 

(within seconds) as the leaf is exposed 

to the often hot, windy environment 

around it. Only using bagged leaves is an 

important practice in acquiring stable, 

more-representative measurements that 

are easily interpreted. Resist the temptation 

to remove the leaf from the foil bag 

even if it makes inserting the sample leaf 

into the chamber more convenient. 

Measuring SWP (fig. 5) after 

the bagged leaf is excised from a 

tree involves inserting the stem 

of a bagged leaf upward through 

the top of the pressure chamber 

and securing the protruding stem 

A B 

in the pressure chamber cap (A). 

Then, placing the bagged leaf in 

the pressure chamber (B). A long 

stem is shown protruding out of 

the top of the chamber (C). Some 

researchers emphasize that the 

stem should not be protruding 

out this much for the most accurate 

measurement of SWP. Other 

researchers have observed 

C D 

that practitioners have more 

difficulty seeing the endpoint 

Figure 5. Basic process of measuring midday SWP with 

a pressure chamber. Photos: A. Fulton and K. Shackel. 

without the longer stem, which 

can also introduce error in 

from the surface of the cut stem and will 

seeing the endpoint. Apply pressure 

appear to glisten (D). With the addition 

inside the chamber and determine the 

of a little more pressure, water will cover 

endpoint for a SWP measurement. Close 

to the endpoint, water begins to exude Continued on Page 10 

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9

Interpreting SWP measurements 

Baseline concept to distinguish weather from irrigation effects 

Because SWP is affected by weather conditions at the time measurements 

are made, readings can vary from one day to the next as the 

weather changes, even if irrigation management and soil moisture are 

relatively stable. This has led to the development of the baseline concept 

for irrigation managers who want to improve upon their interpretation of 

SWP readings for irrigation scheduling. 


Table 1. Baseline SWP (bars) to expect for fully irrigated almonds or 

prune trees under different conditions of air temperature and relative 

humidity. 

Figure 6. Photo of actual SWP measurement in walnut 

using a pressure chamber with digital gauge. Plant 

water status of this walnut tree was -5.67 bars tension. 

Temperature (ºF) Air relative humidity (RH, %) 

Photo: C. Haynes. 10 20 30 40 50 60 70 

75 -7.3 -7.0 -6.6 -6.2 -5.9 -5.5 -5.2 


the entire cross-section of the stem and reach the 

endpoint. 

Most pressure chambers (excluding handheld 

pump-up models) incorporate an adjustable 

metering valve to regulate how fast pressure builds 

inside the chamber. Metering valves should be set 

to increase pressure slowly to lessen the chance of 

missing the endpoint. Operators should set the rate 

the chamber pressurizes slow enough so that it is 

possible to both watch for the endpoint and read 

the pressure gauge at the same time (fig. 6). Experience 

suggests that a pressure increase of 0.25 to 0.5 

bars per second is just about right. When tree water 

status is at low to mild levels, pressure increases 

might be lower. Whereas, when tree water status is 

at moderate and higher levels, pressure increases 

may need to be higher to expedite measurements. 

In addition, less error occurs when pressure entering 

the chamber is quickly stopped at the endpoint 

by using the shut-off valve (NOT the regulator 

valve). The pressure regulator valve is a needle type 

that can be easily damaged from over-tightening to 

stop pressure into the chamber. 

SWP measurements should be completed as 

rapidly as possible after bagged leaves are excised. 

It usually takes an experienced operator 15 to 30 

seconds to take a measurement depending on the 

plant water status. To minimize variability, readings 

should be made within 1 minute of being removed 

from the tree. 

80 -7.9 -7.5 -7.0 -6.6 -6.2 -5.8 -5.4 

85 -8.5 -8.1 -7.6 -7.1 -6.6 -6.1 -5.6 

90 -9.3 -8.7 -8.2 -7.6 -7.0 -6.4 -5.8 

95 -10.2 -9.5 -8.8 -8.2 -7.5 -6.8 -6.1 

100 -11.2 -10.4 -9.6 -8.8 -8.0 -7.2 -6.5 

105 -12.3 -11.4 -10.5 -9.6 -8.7 -7.8 -6.8 

110 -13.6 -12.6 -11.5 -10.4 -9.4 -8.3 -7.3 

115 -15.1 -13.9 -12.6 -11.4 -10.2 -9.0 -7.8 

Table 2. Baseline SWP (bars) to expect for fully irrigated walnut trees 

under different conditions of air temperature and relative humidity. 

Temperature (ºF) Air relative humidity (RH, %) 

10 20 30 40 50 60 70 

75 -4.5 -4.3 -4.2 -4.0 -3.8 -3.6 -3.4 

80 -4.8 -4.6 -4.3 -4.1 -3.9 -3.7 -3.5 

85 -5.2 -5.0 -4.7 -4.4 -4.1 -3.9 -3.6 

90 -5.6 -5.2 -4.9 -4.6 -4.3 -4.0 -3.7 

95 -6.0 -5.7 -5.3 -5.0 -4.6 -4.3 -3.9 

100 -6.5 -6.1 -5.7 -5.3 -4.9 -4.5 -4.0 

105 -7.2 -6.7 -6.2 -5.7 -5.2 -4.8 -4.3 

110 -7.8 -7.3 -6.7 -6.2 -5.6 -5.0 -4.5 

115 -8.7 -8.0 -7.4 -6.7 -6.0 -5.4 -4.8 


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Pythium Wilt Disease of Lettuce 

Causing Diagnostic Challenge 

By: Steven T. Koike | UC Cooperative Extension 

Plant Pathology Advisor | Monterey County 

The development of a new problem on coastal lettuce, Pythium 

wilt, caused confusion and concern for growers in 

California’s Monterey County because the symptoms resembled 

those of other lettuce diseases. Such a situation serves as a 

reminder of the challenge of identifying soilborne diseases in 

crops using only symptoms. 

In contrast to Pythium diseases of spinach, tomato, 

cotton, and other crops, this lettuce pathogen does not cause 

damping-off or symptoms on newly emerged, young lettuce 

Pythium Wilt in Coastal California 

In recent seasons in Monterey 

County’s Salinas Valley, 

significant crop losses 

were caused by Pythium 

wilt disease of lettuce 

(Photo 1). Caused 

by Pythium uncinulatum, 

this disease 

appeared to be only 

recently introduced 

to coastal California, 

and prior to 

2014 was of minor 

importance. However, 

during 2014 

and 2015 seasons, the 

problem spread to a 

number of locations in the 

valley and caused perhaps 30 

percent or more losses in some fields. 

Photo 2. Stunted lettuce plants with Pythium wilt 

disease. A healthy plant is on the left. Photos courtesy: 

Steven Koike 

seedlings. Instead, above-ground Pythium wilt 

symptoms do not show on lettuce until plants are at 

the rosette or older stage. Plants infected at this point 

of growth will be stunted and lag behind healthy lettuce. 

As disease progresses, outer leaves will start to wilt 

during the warmer times of the day and eventually turn 

yellow before becoming brown and dead. In advanced stages, 

Photo 1. Lettuce field severely affected with Pythium wilt disease. 


the entire foliar canopy can collapse 

and die. Diseased plants that survive 

will be small and substandard in quality 

(Photo 2, pg. 12). In the soil, the 

pathogen first attacks the small feeder 

roots of the lettuce, making them soft 

and brown gray in color. Late in disease 

development the taproot will be 

darkly discolored and the entire root 

system can be rotted (Photo 3). 

Pythium uncinulatum, like most 

Pythium species, produces swimming 

spores (zoospores) that are released 

and move within the water film in the 

soil. Water flow from irrigation, flooding, 

and movement of soil via tractors 

and equipment can spread this 

pathogen. In addition to zoospores, 

the pathogen also produces a type of 

spore (oospore) that is encased within 

a spiny outer covering (oogonium) 

(Photo 4). It is the oospore that allows 

the pathogen to survive in the soil in 

the absence of susceptible plants. Pythium 

uncinulatum is host specific to 

lettuce and apparently does not infect 

other vegetable crops such as broccoli, 

cabbage, carrot, onion, pepper, radish, 

spinach, or tomato. 

Symptoms Pythium Sclerotinia Botrytis 

Stunted plants Yes Yes Yes 

Wilted leaves Yes Yes Yes 

Yellowed 

leaves 

Collapsed 

plants 

Decayed 

crowns 

Rotted root 

system 

Yes Yes Yes 

Yes Yes Yes 

No Yes Yes 

Yes No No 

Table 1. Similarity of disease symptoms for three soilborne 

pathogens of lettuce. 

Pythium Wilt Confused 

With Other Diseases 

eases. Stunting of plants, 

wilting and yellowing 

of leaves, and 

collapse of plant 

foliage can also 

be caused by 

lettuce drop 

(pathogen: 

Sclerotinia 

minor) and 

Botrytis 

crown rot 

(pathogen: 

Botrytis cinerea) 

(Table 1). 

Differentiating between 

these three diseases 

therefore requires 

careful examination of 

all plant tissues (leaves, 

crown, roots) as well as 

lab-based analysis. 

In approaching this 

diagnostic challenge, 

first note if the lettuce 

plant has the general 

foliar symptom profile 

of stunting, wilting, yellowing, 

and collapsing. 

Secondly, the crown 

should be carefully 

examined. If the 

crown is discolored, 

soft, decayed, and supporting 

visible fungal 

growth, then the 

disease is likely Sclerotinia 

lettuce drop 

or Botrytis crown rot; 

if the crown is solid 

and intact and there 

are no signs of fungal 

structures, then Pythium 

wilt is a possibility. 

Finally the root 

system, taproot plus 

attached feeder roots, 

must be inspected in 

detail. Carefully dig 

up the root system 

and wash off the soil. 

If the roots are dark and rotted, Pythium 

wilt must be suspected. Sclerotinia and 

Botrytis pathogens generally do not infect 

roots at all. These three steps can assist in 

arriving at a tentative diagnosis in the field. 

As for most plant diseases, confirmation of 

Pythium wilt and other problems can only 

be accomplished following laboratory test- 

Photo 4. Microscopic, spherical, 

spiny structures (oospores within 

oogonia) help Pythium 

uncinulatum survive in 

the soil between lettuce 

crops. Photo Courtesy: 

Steven Koike 

ing and analysis. 

Note that there 

is one more confounding 

factor: two 

Photo 3. Dark, rotted root system of lettuce infected with Pythium 

uncinulatum. Healthy lettuce roots are on the right. 

Because Pythium wilt causes 

above-ground, foliar symptoms that 

are not distinctive or unique, this 

problem was initially misdiagnosed 

and confused with other lettuce dislettuce 

infecting virus pathogens, Impatiens 

necrotic spot virus (INSV) and 

Lettuce necrotic stunt virus (LNSV), can 

cause foliar symptoms that may resemble 

those caused by the early stages of Pythium 

wilt. INSV and LNSV both infect lettuce 

and result in declining plant foliage 

that is yellowed and necrotic. The field 

professional must therefore also account 

for the possibility of these viruses during 

the diagnostic investigation. 

The Challenge of Diagnosing 

Soilborne Diseases 

One reason why soilborne pathogens 

are problematic is that they are 

difficult to diagnose in the field. Besides 

the Pythium wilt example, there are 

many other situations in which disease 

identification based only on symptoms is 

problematic. Lettuce growers in coastal 

California face two damaging vascular 

wilt diseases: Fusarium wilt and Verticillium 

wilt. These two diseases cause 

very similar symptoms of overall plant 

decline, wilting, collapsing, and discoloration 

of the internal vascular tissue of 




13


taproots (Table 2, Pg. 14). The 

two wilts may be differentiated 

in that Verticillium wilt symptoms 

usually show on mature 

plants that are close to harvest, 

while Fusarium wilt symptoms 

can occur on both young and 

mature plants. However, the 

buildup of ammonium in soils 

can damage the central cores 

of lettuce taproots. Lettuce 

roots exposed to high levels 

of ammonium therefore may 

look like a Fusarium wilt case. 

Again, to know precisely the 

cause of declining lettuce plants 

that have vascular discoloration 

in taproots, one must have the 

plants tested by a pathology lab. 

Symptoms Fusarium Verticillium Ammonium 

Yellowed leaves Yes Yes Yes 


Collapsed plants Yes Yes Yes 

Vascular discoloration Yes Yes Yes 

Decayed crowns No No No 

Rotted roots No No No 

Symptomatic young plants Yes No Yes 

Symptomatic mature plants Yes Yes No 

Table 2. Similarity of disease symptoms for lettuce affected by Fusarium wilt, Verticillium wilt, and 

ammonium toxicity. 

Strawberry growers face a 

similarly daunting task of trying 

to identify soilborne diseases. 

Three significant diseases have 

ISOMATE 

virtually identical symptoms of off-color, gray 

green foliage, wilting of leaves, collapsing of 

plants, dark internal discoloration of strawberry 

crowns, and eventual death of the plant (Table 

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3, pg. 15). Because Macrophomina crown 

rot, Fusarium wilt, and Phytophthora 

crown rot share all of these symptom 

features, it is not possible to know which 

one is present in the field. Two of these 

problems, Macrophomina crown rot and 

Fusarium wilt (Photo 5), are very damaging 

to strawberry plantings and in addition 

have been steadily spreading; both pathogens 

are now found in all of the major 

coastal strawberry production regions in 

California. 

Why Accurate Diagnoses are 

Essential in Production 

Agriculture 

Some might feel that “a dead plant is 

a dead plant” and that knowing the exact 

name of the responsible pathogen or factor 

is not that important. As an extension 

plant pathologist, I would suggest that it is 

absolutely essential in today’s competitive 

agricultural world to know precisely the 

cause of a problem. Accurate pathogen 

identification always has been the first 

required step in fashioning an integrated 

pest management (IPM) program for dealing 

with plant diseases. Pathogen identification 

enables the grower to know which 

crops are susceptible to the agent, which 

crop cultivars might be advisable to plant 

due to genetic resistance, how the pathogen 

gets around and is spread, and other 


Symptoms Macrophomina Fusarium Phytophthora 

Older leaves affected first Yes Yes Yes 

Gray green foliage Yes Yes Yes 


Collapsed plants Yes Yes Yes 

Discolored crowns Yes Yes Yes 

Death of entire plant Yes Yes Yes 

Table 3. Strawberry plants affected by Macrophomina, Fusarium, and Phytophthora all show very similar symptoms. 

pertinent biological information. 

Since most plant pathogens 

cannot be confirmed without 

lab analyses, accurate disease 

identification will require close 

collaboration between growers, 

field personnel, and extension or 

private laboratories. 

Managing Pythium Wilt 

and Other Soilborne 

Pathogens 

A 

B 

The following management 

strategies should be considered 

when dealing with Pythium wilt 

disease. These measures also 

illustrate general principles that 

can be adopted for controlling 

other soilborne diseases. (1) 

Avoid planting lettuce into fields 

with a known history of the 

problem. (2) For infested fields, 

rotate to non-lettuce crops. Various 

research studies demonstrated 

that Pythium uncinulatum is 

host-specific to lettuce and will 

not infect other vegetable crops. 

(3) Implement field sanitation 

practices to minimize the movement 

of contaminated soil from 

infested to clean fields. (4) Be 

aware that surface water runoff 

from infested fields may be 

contaminated with the pathogen. 

Flooding events may also spread 

the pathogen to previously clean 

fields. (5) Prepare beds so that 

drainage of water is enhanced, 

since all Pythium species are favored 

by wet soil conditions. (6) 

C 

Photo 5. Strawberry plants infected with Macrophomina (A and C) or Fusarium (B and D) have 

identical symptoms consisting of wilting and collapse of leaves, discoloration of internal crown 

tissue, and death of the entire plant. Photos Courtesy: Steven Koike 

Manage the irrigation so that excessive soil 

moisture is avoided. (7) The effectiveness of 

fungicides for controlling Pythium wilt in 

California is currently unknown and will 

require field trials. (8) The planting of lettuce 

cultivars that are resistant to P. uncinulatum 

would be the preferred IPM method 

for control; however, such cultivars are not 

available at this time. (9) The application of 

pre-plant treatments such as soil fumigants 

D 

and biological control agents are not relevant 

at the moment for Pythium wilt of lettuce; 

however, such measures should certainly be 

considered for strawberry and other crops and 

their respective soilborne pathogens. 

Comments about this article? We want to hear 

from you. Feel free to email us at article@ 

jcsmarketinginc.com 



15

FUMIGATION ALTERNATIVES FOR TREE AND VINE CROPS 

Are there novel materials for 

soil fumigation? 

Orchard fumigation rig (background) with soil sealing rig (foreground) 

Photo Courtesy: Andrea Westphal 

By: Andreas Westphal | Department of Nematology, University of California, Riverside, Kearney Agricultural Research and Extension center, Parlier, CA 

By: Mike Stanghellini | Director of Research & Regulatory Affairs, TriCal Inc., Hollister, CA 

Sustainability of many crops is put at 

risk by the build-up of soil-borne 

plant pathogens. While yield-reducing 

effects of air-borne maladies can often 

be effectively mitigated by pesticide 

inputs, soil-borne problems are much 

more challenging. By definition, pathogens 

causing these diseases persist in the 

complex environment of the soil matrix. 

On the one hand, this complexity 

increases the time that it takes for these 

culprits to spread. On the other hand, 

soil complexity renders suppression 

of these pathogens and pests generally 

more challenging than air-borne diseases 

and pests. In fact, soil-borne maladies 

are often the key components that 

determine how frequently a crop or crop 

group can be grown in specific fields. 

These restrictions lay the foundation for 

crop rotation programs. For example, 

in nematode management, the use of 

non-susceptible host plants of specific 

nematode pests may be prescribed to 

avoid the build-up of injurious nema- 

tode populations. Such strategies can 

be very effective when crops of similar 

value and equipment requirements are 

used. The situation becomes challenging 

when high-value crops are produced 

in highly specialized systems where a 

diversion to less profitable crops is not 

feasible, such as when high land rental 

costs introduce additional economic factors 

that come into play. In some cases, 

limited crop rotation alternatives exist 

because of the wide host range of pathogens 

or pests. For example, root-knot 

nematodes have very wide host ranges, 

and a rotation based on various susceptible 

vegetable crops would be unfit to 

reduce infestation levels in fields. 

Methyl Bromide 

For decades, soil fumigation has 

been used to reduce these important 

crop-limiting pests by rendering pestfree 

(or effectively managed) soil environments. 

Since its registration in the 

US in 1961, methyl bromide had been 

an effective tool to reduce soil-borne 

maladies. One main strength of methyl 

bromide is its versatility under different 

application conditions. Its high vapor 

pressure coupled with a greater-than-air 

density allowed methyl bromide to effectively 

penetrate complex soil matrices 

that differed considerably in temperature, 

moisture level, and texture. Concerns 

about methyl bromide’s ozone-depleting 

potential in the stratosphere 

led to its phase-out under the Montreal 

Protocol. After its phase-out from 

general use in the US in 2005, Critical 

Use Exemptions (CUE) were granted for 

selected applications where technical alternatives 

were not available. This helped 

protect against market disruptions in 

strawberry and other high-value crop 

industries in the US and other countries. 

The 2016 growing season marked the 

end of the CUE process in the United 

States. For 2017 and future years, the 



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With the phase-out of non-QPS methyl 

bromide, the proven mainstays of soil 

fumigation have become more important; 

namely, 1,3-dichloropropene (1,3-D) and 

chloropicrin-containing products. The 

1,3-D formulations, e.g., Telone products, 

are experiencing a resurgent popularity. 

Nationwide, 1,3-D-containing products 

have been used since the 1950s, but its use 

in California was temporarily suspended 

in1990 after ambient air monitoring 

programs detected high concentrations in 

the San Joaquin Valley air basin. Products 

containing 1,3-D were reintroduced for use 

in California in 1995, with the addition of 

several strict control measures. Beginning 

January 2017, the application of 1, 3-D is 

limited to 136,000 pounds per township 

(=36 square mile area) per year in order to 

maintain ambient air concentrations below 

the California Department of Pesticide 

Regulation’s threshold. Previous regulations 

that allowed for a “carry-over” of unused 

amounts of the annual township allotment 

to the following year are no longer in effect. 

These restrictions make grower access to 

1,3-D in some California counties challenging 

when multiple crops potentially benefit 

from the application of the material. Recent 

research has demonstrated that the use of 

totally impermeable film (TIF) significantly 

reduces fugitive emissions and can allow 

for reductions of application rates without 

loss of efficacy in pathogen and pest suppression. 

However, regulatory constraints 

remain a limiting factor of 1,3-D use in 

California. Grower demand exceeds regulatory 

permitted use. 

Chloropicrin use has also increased as 

the availability of methyl bromide decreased. 

For decades, most chloropicrin was 

used in combination with methyl bromide, 

but it also has a long history of use as a sole 

active ingredient because of its excellent 

fungicidal properties. Because of its “warning 

agent” (tear-gas-like) properties, it is 

used in structural fumigation when otherwise 

odorless gases are used. For example, it 

was used in small doses to warn against inadvertent 

exposure to methyl bromide, and 

now sulfuryl fluoride, both of which are 

© 2017, Trécé Inc., Adair, OK USA • TRECE, PHEROCON and CIDETRAK are registered trademarks of Trece, Inc., Adair, OK USA 

TRE-1034, 1/17 


Table: Active ingredients and trade names of potential and actual soil fumigant and biocide materials at various levels of development a 

Active ingredient Product b Application rates c Pest 

controlled d 

1,3-D 

(1,3-dichloropropene) 

Chloropicrin 

MITC generators 

(methyl-isothiocyanate) 

AITC 

(allyl-isothiocyanate) 

DMDS 

(dimethyl disulfide) 

EDN 

(ethanedinitrile) 

Telone II, Telone EC, 

mixes w/ chloropicrin 

Chloropicrin 100 Tri-Clor, 

mixes with 1,3-D 

Vapam HL 

K-PAM HL 

Signal word(s) 

9-33.7 gal/A e N, F, (W) f Warning 

7-25 gal/A F, (N) f Danger, Poison 

50-100 gal/A N, F, W Danger, Poison 

Dominus 10-40 gal/A N, F, W Danger 

Paladin 37-54.2 gal/A N, F, W Danger 

EDN N/D g N, F, W Danger 

Cyanamide 50% N/D f N/D g N, F, W Danger, corrosive 

a 

Data are for informational purposes only. Always consult the current safety data sheet (SDS) and pesticide label before using chemical 

compounds. 

b 

These are examples of trade-named products. There may be other products with the same active ingredients that may have similar 

properties as the ones named here. 

c 

Application rates are based on currently available label information. 

d 

Efficacy according to currently published information and experience; additional information may become available: N = nematodes, 

F= fungal pathogens, W= weeds; parentheses indicate partial activity. 

e 

Maximum label rate in California. 

f 

When applying by shanks, improper soil moisture content may reduce movement of material. 

g 

N/D: Not determined; information not yet available. 

odorless, when conducting residential 

fumigations for termite control. 

In the soil, chloropicrin is known to 

have synergistic, or complimentary, 

pesticidal activity when combined 

with methyl bromide or 1,3-D. More 

and more frequently, due to the loss of 

methyl bromide and current restrictions 

on 1,3-D, chloropicrin is used as 

a sole active ingredient for soil fumigation. 

It can be effective against soilborne 

fungal and bacterial pathogens, 

as well as some arthropod pests, but is 

generally not suitable as a stand-alone 

nematicide due to its inability to penetrate 

woody tissues (like old roots 

which may harbor nematodes), and 

is not effective on weed seed banks in 

the soil. Recent studies have demonstrated 

that chloropicrin is a valuable 

material when orchard growers are 

confronted with “replant disorders”; 

conditions which may be encountered 

when planting the same or similar 

crop back-to-back, e.g., almonds 

following almonds. 

Another long-known chemistry 

are the MITC (methyl isothiocyanate) 

generators: metam 

sodium (e.g., Vapam® HL), metam 

potassium (e.g., K-PAM® HL), and 

dazomet (e.g., Temozad). These 

materials quickly break down after 

application to form MITC, which is 

active against weed seeds, soil-borne 

pathogens and other pests. These 

materials can be applied via shank 

application or chemigation through 

the drip irrigation system (metam 

sodium and metam potassium) or as 

a granule (Temozad) applied using 

scoops, shakers, shanks, drop-type 

fertilizer spreaders, or other suitable 

equipment. Research on perennials 

has demonstrated that in these high 

value crops, the active ingredient 

needs to be delivered to the site of 


Unfumigated (Foreground) Chloropicrin fumigated 

(Background) 



19


action in the soil. Typically, 

this is done with soil 

drenches using irrigation 

water, whereby the biocidal 

material is dissolved in the 

irrigation water, which is 

then applied at or near the 

soil surface to percolate the 

soil matrix. Depending on 

the soil depth targeted, this 

could be up to 6 inch/A of 

water for a five-foot depth 

of application. The key 

to ensure efficacy of this 

material is delivery to the 

target site. Some air quality 

issues limit the use of this 

material. The water-drench 

logistics for application 

as pre-plant material in 

deep-rooting perennials 

somewhat hinders its’ 

widespread adoption. 

Allyl isothiocyanate 

(AITC) is the new biofumigant 

active ingredient 

formulated as Dominus®. 

This synthetically-produced, 

but chemically 

identical, version of the 

naturally-occurring compound 

present in many 

Brassica species is used 

for biocidal treatments. 

Although general knowledge 

of plant-derived 

AITC is robust, its development 

as a pure-form 

soil fumigation product is 

recent. Currently, AITC 

can be applied by shank 

application or drip irrigation 

(“chemigation”) for 

use in annual crops, but 

has less demanding labels 

than the traditional soil 

fumigants. For example, 

Dominus has no, or very 

small, buffer zones and 

its use currently does 

not require a written 

Fumigant Management 

Plan (a highly detailed, 

Almond trees planted at the same time in fumigated soil (lower image) 

and non-fumigated soil (upper image). 


site-specific, pre-application record of 

intended use). Like MITC generators, 

AITC may exhibit slow movement in the 

soil, suggesting that its use for perennial 

crops may need more research to optimize 

its utility in scenarios having larger 

soil volumes that need to be treated. Like 

other materials, AITC could be used in 

crop termination, whereby application 

is done after final harvest to ‘burn down’ 

the roots and reduce pathogen pressure 

before the crop residue is tilled under for 

decomposition. Although AITC product 

labels have generally less restrictive 

requirements than the traditional fumigants, 

its application does entail the use 

of proper PPE due to corrosiveness and 

skin irritation potential. This should not 

deter from use if high efficacy rates can 

be shown. Registration of this material 

was granted federally several years ago, 

and is currently registered in 27 different 

states. Registration in California is 

pending. 

Another material used commercially 

in some US states is dimethyl disulfide 

(DMDS), formulated as Paladin 

or Paladin EC. Outside of agriculture, 

DMDS is primarily used as catalyst 

in hydrocarbon processing. Its acute 

toxicity and other exposure effects are 

such that it is considered reasonably safe 

to use. In fact, low doses of this material 

are used as food additives to impart 

a pungent garlic odor. However, at 

elevated concentrations, this same odor 

can be highly objectionable, and so it is 

regulated based on its potential to be an 

odor nuisance. DMDS soil fumigation 

product labels currently mandate the use 

of low-permeability tarps for mitigation 

of the odor of this effective nematicide, 

Aqueous cyanamide formulations at 

10 and 50 percent a.i., fall into Pesticide 

Categories III or II, respectively, 

and constitute a candidate for biocidal 

treatments. For tree and vine crops, 

this non-fuming, non-odorous, highly 

water soluble biocide will be tree site or 

strip applied and further diluted 250 to 

500-fold to reach 99 percent of the target 

sites. The active ingredient metabolizes 

in a cascade of nitrogenous materials 

within soil but is also adequately systemic 

to kill live roots, endoparasitic life 

stages of nematodes within and plant 

tissues above. It does not penetrate well 

into dead plant tissues. Application rates 

and introduction of nitrogen amounts 

still need to be worked out and will likely 

vary for different crops and soil textures. 

This liquid is currently available globally 

as a plant growth regulator under several 

brand names. It is also commercialized 

for its lethal actions upon enzymes, 

which may explain plant responses 

that are visibly more complex than just 

an overdose of nitrogen. This solution 

is well-suited for use in replant problem 

sites for the so-called “Starve and 

Switch” strategy, meaning the reduction 

of pathogenic organisms of a particular 

crop and the following change to 

different crop genetics. The commercial 

development of such formulations is at 

its beginning. 

A quite different material currently 

under experimental exploration is 

ethanedinitrile (EDN). This material 

has a lower boiling point and a higher 

vapor pressure than methyl bromide. 

At ambient temperature it is a gas, and 

thus requires pressurized handling and 

potentially novel application equipment. 

EDN has a short half-life in soil. 

Current research is focused on safe and 

uniform application, and improving its 

residence time in soil. Crop trials have 

shown its potential to be a broad-spectrum 

fumigant. 

In summary, in the “post methyl 

bromide era”, the older, and proven, 

chemistries like 1,3-D, chloropicrin, 

and the MITC generators are in high 

demand, and are often used in various 

combinations; while newer chemistries 

undergo optimization as methyl bromide 

alternatives. Work on these newer materials 

is ongoing, where adjustments and 

technical advancements may be required 

before some of them can be widely 

used. Overall, the concept of a “drop-in 

replacement” for methyl bromide very 

likely needs to be shelved, as agricultural 

production converts to the concept of 

Integrated Pest Management, i.e., the use 

of multiple pest control strategies and 

tactics for the management of soil-borne 

maladies for high-value crop production. 

Comments about this article? We want 

to hear from you. Feel free to email us at 

article@jcsmarketinginc.com 

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® 



21

Pesticide Safety in 

Orchard 

the 

By: Amy Wolfe | MPPA, CFRE | President and CEO, AgSafe 

As we spray our orchard floors in 

preparation for the harvest that is 

just around the corner it is important 

that we consider pesticide safety. This 

is such a busy season for growers that 

employee safety and training often do 

not get the time and energy needed. To 

help tackle these important pesticide 

safety elements it helps to put them into 

five categories: 

• Personal protective equipment 

• Decontamination 

• Employee training 

• Emergency medical care 

• Label requirements 

Personal Protective 

Equipment 

Personal protective equipment (PPE) 

serves as a protective barrier between the 

applicator and the pesticide. While pesticide 

use in orchards is common practice, 

it is important to remember that pesticides 

are used to kill pests, which means 

it has the potential to harm the applicator 

if not used safely. 

Prior to spraying read the label PPE 

requirements—the label is the law and 

both owners and employees must follow 

the PPE section. Consider the Rely 280 

label. The PPE section is in bold and 

breaks out the PPE requirements for 

handlers versus mixer/loaders. Handlers 

must wear a long-sleeved shirt, long 

pants and shoes plus socks. As a good 

rule of thumb, keep this as the minimum 

PPE that should always be worn when 

applying. In addition to the minimum 

requirements, Rely 280 calls for chemical 

resistant gloves and specifies what material 

the glove is made from. The Department 

of Pesticide Regulation (DPR) 

has a glove category selection key card 

that helps you navigate glove material 

requirements. 

The Department of Pesticide Regulation has a glove category selection 

key card that helps you navigate glove material requirements. 

In addition to the label, employees 

have extra PPE requirements per Title 

3 of the California Code of Regulations 

(3CCR). This regulation states that the 

employer must provide all necessary 

PPE. When an employee is going to 

make a pesticide application, under 

3CCR Section 3738, he or she must 

also wear chemical resistant gloves 

and protective eyewear, even when not 

required by the label. Another important 

element to note, any employee handling 

a “DANGER” or “WARNING” product 

must wear coveralls. These are just a few 

of the highlights on PPE regulations. Be 

sure to review 3CCR 3738 for the full 

regulation: http:// 

www.cdpr.ca.gov/ 

docs/legbills/ 

calcode/030302. 

htm#a6738. 

Decontamination 

Even in the 

best of situations 

sometimes PPE 

or equipment fails 

and employees 

become contaminated 

with 

pesticides. In 

these scenarios, a 

properly stocked 

decontamination 

kit can help prevent significant injuries. 

Under 3CCR 6734, employers are required 

to provide decontamination facilities 

for handlers. Theses kits or facilities 


need to have the following items: 

• Sufficient water, at least 3 gallons per 

handler 

• Soap 

• Single use towels 

• One clean pair of coveralls 

• One pint of eyewash immediately 

available if the pesticide label 

requires protective eyewear, although 

best practice is to provide 

eyewash in the kit at all times 

The decontamination kit can be at 

the mix/load site as long as it is not more 

than quarter mile from the handler. In 

addition to the items listed above, at the 

mix/load site there needs to be an emergency 

eye flushing system. The regulation 

has very specific requirements as to 

the amount of water and flow. See 3CCR 

6734 for details: http://www.cdpr.ca.gov/ 

docs/legbills/calcode/030302.htm. 

Employee Training 

Training serves as the backbone to 

any safety program and with pesticide 

training, 3CCR 6724 specifically states 

what is required. Employees need to be 

trained prior to handling pesticides, on 

every pesticide label they will handle, 

anytime a new pesticide is introduced to 

the operation and annually thereafter. 

The elements covered during pesticide 

training are robust. Recently DPR 

adopted the Environmental Protection 

Agency’s (EPA) revised Worker Protections 

Standard (WPS) which increased 

the number of training elements. These 

elements include: 

• Routes by which pesticides can enter 

the body 

• Signs and symptoms of pesticide 

exposure 

• Emergency first aid procedures 

• Heat illness prevention 

• Warnings about taking pesticides 

home 

• Proper decontamination 

Training must be given in such a way 

that the employee can understand, correlate 

with the grower’s written pesticide 

program and be documented. 

Emergency Medical Care 

In severe cases employees may need 

to be taken to emergency care. This is 

why 3CCR 6726 has requirements about 

emergency medical postings. Emergency 

medical care must be planned for 

employees in advance. Employees shall 

be informed of the name and location 

of the facility where care is available. 

This information needs to be posted 

in a prominent place in the workplace. 

This information also needs to be filled 

out on the Pesticide Safety Information 

Series A8 and A9 forms. 

It is vitally important that this information is 

readily available to employees. An easy 

fix is to attach a key chain to the equipment 

keys used for application with the required 

information. 

For the entire Pesticide Safety Information 

Series visit; http://www.cdpr. 

ca.gov/docs/whs/psisenglish.htm. It is 

vitally important that this information is 

readily available to employees. An easy 

fix is to attach a key chain to the equipment 

keys used for application with the 

required information. 

Label Requirements 

As previously noted, the label is the 

law. The pesticide label covers everything 

from application rate and PPE to first 

aid and application restrictions. Among 

application restrictions are the restricted 

entry interval and pre-harvest interval. 

Restricted entry interval (REI) as 

defined by DPR, is the period of time 

after a field is treated with a pesticide 

during which restrictions on entry are in 

effect to protect persons from potential 

exposure to hazardous levels of pesticide 

residues. Basically, the REI is the amount 

of time that has to elapse before anyone 

can enter the field without proper PPE. 

In regards to employee safety, handlers 

should always check the REI time on a 

label prior to spraying and follow notification 

regulations so that other employees 

know not to enter that treated field. 

Pre-harvest intervals (PHI) are different 

than REIs in that this is the amount 

of time that has to elapse before you can 

harvest your orchard and have the nuts 

be safe to eat. Pre-harvest intervals are 

intended to provide a period between 

the application of a pesticide and harvest 

so the crop will meet the established 

pesticide residue tolerance and protect 

the public from possible exposure to 

excessive residues. For example, the Goal 

2XL label states “do not apply within 15 

to 30 days of harvest of almonds,” and 

“within 7 days of harvest of walnuts.” 

Unfortunately, this information on the 

label is not on the front page, it is buried 

on page 31 of 33, emphasizing the need 

to review the entire label prior to application. 

As harvest rapidly approaches, be 

sure to consider these five essential operational 

areas to ensure pesticide safety 

for employees during this busy time of 

year: personal protective equipment, 

decontamination, employee training, 

emergency medical care and label requirements. 

For more information about pesticide 

safety, or any worker safety, health, human 

resources, labor relations, or food 

safety issues, please visit www.agsafe.org, 

call us at (209) 526-4400 or via email at 

safeinfo@agsafe.org. 

AgSafe is a 501c3 nonprofit providing 

training, education, outreach and tools 

in the areas of safety, labor relations, 

food safety and human resources for the 

food and farming industries. Since 1991, 

AgSafe has educated nearly 75,000 employers, 

supervisors, and workers about 

these critical issues. 






23

California Pistachio 

Salt Tolerance Update 

by: Blake Sanden, Louise Ferguson and Beau Antongiovanni 

The classic concept of crop salt tolerance is over 

simplified. Focusing only on rootzone salinity this 

calculation consists of a single soil saturation extract 

salinity threshold (ECe) with a “% relative yield” decline 

function (Figure 1). 

Research 

This approach minimizes the real world variability 

in actual tree growth and yield due to additional specific 

ion toxicities, nutritional problems often associated 

with high pH soils and soil textural problems causing 

water logging/anoxia and possible disease. The current 

salinity tolerance function for California pistachios is 

essentially the same as cotton. It was developed from a 

small plot study during the eight to 13th leaf years in 

a commercial orchard in northwestern Kern County 

from 1997-2002 to give a final threshold of 9.4 dS/m 

ECe and an 8.4 perent relative yield decline above that 

level. These values were confirmed for seedling growth 

in saline sand-tank studies at the United States Department 

of Agriculture (USDA) Salinity Lab in Riverside, 

California. 

Figure 1. Currently accepted pistachio salt tolerance curve compared to 

cotton, alfalfa and almond (Sanden and Ferguson, 2004) 

A second large scale field study applied fresh and 



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25

Figure 2. Field locations of Kern County expanded 2014-16 pistachio salinity study. 


saline irrigation treatments (0.5 to 5.2 

dS/m EC) from planting through 10th 

leaf. Trees were commercially harvested 

starting in 2011. Average 2011-14 root 

zone salinity ranged from 2.5 to 13.2 

dS/m and caused a significant edible 

inshell yield reduction of 96 to 235 lb/ 

ac (depending on rootstock) in the 

combined 4 year yield: a one to three 

percent decline for every unit EC (dS/m) 

increase over 6 ds/m. 

Expanded Salinity 

Survey 

In 2014, a greatly expanded salinity 

survey including 10 commercial fields 

(9th – 15th leaf) was initiated in western 

Kern County with 136 individual 

tree data points ranging from a threeyear 

average root zone (five foot depth) 

salinity of 1.6 to 20.5 dS/m (Figure 2). 

The study sites, spread across 200 square 

miles with a total field size of 1330 acres) 

were specifically selected to incorporate 

a wide range of soil textural and chemical 

differences such as water-logging, 

high pH and varying concentrations of 

sodium, chloride and boron as much as 

possible within each orchard. 

We selected three to four areas in 

each field where Area 1 appeared least 

saline and had the biggest trees and Area 

4 appearing most saline with smaller 

trees (Figure 3). In addition, we used repeated 

measurements of electromagnetic 

conductance 

at the base of 

monitoring 

trees using 

a hand-held 

Geonics EM-38 

DD (Figure 3). 

This is a rapid 

assay device 

that is non-intrusive—simply 

emitting a 

magnetic signal 

of known 

strength at 

one end of the 

device and 

recording the 

strength of the 

‘conductance’ 

received at the 

other end. As 

the salinity 

and water content increase, so does the 

conductance, which is often called the 

EMa (apparent electro-magnetic conductivity), 

and subsequently correlated 

to a conventional laboratory ECe from 

a soil sample to give an ECa (apparent 

electroconductivity). 

Figure 3. Area 1 with average rootzone ECe of 12.9 dS/m 

(‘summed’ EMa = 241 mS/cm) compared to Area 4 of the same field 

with an average rootzone ECe of 9.0 dS/m (‘summed’ EMa = 877 

mS/cm). 


Figure 3 (pg. 26) perfectly illustrates 

the insufficiency of using the classic ECe 

threshold concept as the main driver for 

tree growth and yield decline. The Area 

1 tree has almost double the canopy volume 

of Area 4, but the average rootzone 

ECe from 2014-16 is actually higher 

for Area 1 (12.9 dS/m) compared to 

Area 4 of the same field with an average 

rootzone ECe of 9.0 dS/m. Whoa—that 

makes no sense—the tree with less salt 

is smaller?! What the lab ECe salinity 

does not take into account is the high 

pH, bad sodic silty clay structure that 

makes Area 4 prone to water-logging. 

We used a somewhat novel approach 

taking EM38 measurements right at the 

single-line drip hose and 30 inches away 

from the hose to get a larger snapshot 

of the rootzone. We then summed the 

resulting four horizontal and vertical 

EMa readings for a “summed” conductance. 

Doing this we find Area 1 has a 

summed EMa of 241 mS/cm and Area 4 

was 877 mS/cm—fully 360 percent higher 

conductance for Area 4 compared to 

Area 1, and higher conductance means 

more salt and water logging. Thus, the 

EM38 provided a superior integration of 

the combined impact of salinity and soil 

structure on final tree growth. 

hundreds of measurements per hour as 

opposed to three to four soil cores—and 

it’s integration of excessive water logging 

problems. 

Blake L Sanden, Farm Advisor 


1031 South Mount Vernon Avenue 

Bakersfield, CA 93307, USA 

(661) 868-6218 

blsanden@ucdavis.edu 

Louise Ferguson, Pomology Extension 

Specialist 

Department of Plant Sciences 

3045 Wickson Hall 

Davis, CA 95616 

530-752-0507 

lferguson@ucdavis.edu 

Craig E. Kallsen, Farm Advisor 


1031 South Mount Vernon Avenue 

Bakersfield, CA 93307, USA 

(661) 868-6221 

blsanden@ucdavis.edu 




Figure 4 illustrates the three-year 

summed yield decline as a function of 

rootzone ECe to a depth of five feet. The 

trend is highly significant, and similar 

to the 10 year field trial preceding this 

survey: resulting in a yield reduction 

of 144 to 351 lb/ac (three year cumulative 

inshell yield) for every unit ECe > 

6.5 dS/m. Definitely a lower yield loss 

salinity “threshold” then we published 

13 years ago, but the scatter under the 

curve is large (R2 = 0.107)—indicating 

the multiple other factors affecting tree 

growth and yield. Figure 5 uses the 

“summed” EM38 conductivity (EMa) 

as an estimator of yield decline and 

improves the R2 to 0.207 (Regressing the 

natural log transformed EM38 readings 

with the lab ECe rootzone salinity gave 

an R2 = 0.695, data not shown.) 

Figure 4. Three year cumulative pistachio yield as a function of rootzone salinity. 

No Perfect Tool 

So there is no perfect tool for 

indexing soil and salinity impacts on 

pistachio yield, but the use of the EM38 

shows promise both in it’s ease of use— 

Figure 5. Three year cumulative pistachio yield as a function of EM38 “summed” 

EMa readings. 



27

Remote Sensors for 

Precision Ag at West Hills College 

By Terry Brase | Precision Ag instructor at West Hills College 

In the previous article of this series, 

Unmanned Aerial Systems (UAS) 

were discussed. For all of the attention 

that UAS get, it is just a piece of the 

puzzle. First of all the unmanned aerial 

vehicles are only one type of platform 

for capturing imagery; there are also 

satellites, manned flights, and ground 

based. Second, platforms are not even 

the most important part of the puzzle. 

The imagery that shows how a crop is 

doing or provides information is the 

important part. That leads us this month 

to the sensors or cameras that are used 

to capture the imagery. 

Sensors in agriculture should be a 

bigger deal than UAS, but they aren’t as 

cool so they don’t get all the headlines. 

They are like the guy that is in the background 

doing all the work, but doesn’t 

get the credit. 

Sensors are a big topic, so this is 

actually going to be a two part article. 

This month will be “remote sensors”; 

next month will be “contact sensors”. 

Remote sensors do not actually touch or 

“contact” the object or materials they are 

sensing, therefore they are remote. 

The difference between a sensor and 

a camera also needs to be established, 

though the terms are commonly used 

interchangeably. I once took a group 

of students to visit an aerial imagery 

service company that had just purchased 

a sensor for approximately $1 million. 

Before the tour, I cautioned the students 

that when this sensor was discussed, it 

should not be called a camera. Of course 

upon arrival, the tour guide referred to 

the sensor... as a camera. He corrected 

himself when he saw the student’s 

reaction. 

A camera most properly uses film 

and a shutter to allow light to briefly “expose” 

the film. There is a light sensitive 

chemical on the film that reacts to the 

various types of light and turns color. 

The resulting photograph is a chemical 

process. 

Instead of film, a sensor has a “detector” 

that captures the amount of light 

when a shutter is used to expose it. This 

is an electronic process and results in a 

digital value…thus the term digital camera. 

Digital cameras use sensors to create 

imagery. One problem with sensors in 

digital cameras is that the detectors only 

capture the amount or strength of the 

light and not the color. To solve this, 

most digital cameras separate the light 

(using a type of prism) and then have 

filters that only allow one color to expose 

each of three different sets of detectors; 

one for the “red”, one for the “green”, and 

one for the “blue”. This is known as RGB 

image and when all three are combined 

and displayed in their proper colors, a 

natural color image is the result. 

Higher quality sensors don’t separate 

the light to individual filters and then re- 



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29


combine. They have one set of detectors 

within a sensor which allows the user to 

capture a very specific color. This allows 

more control and thus better analysis. 

It is also important to understand 

what light and color are. There is a wide 

range of energy coming from our sun, 

with a very small part of it as visible 

light. This light is in the form of waves 

of energy that are differentiated by the 

lengths of the waves. Each wavelength 

reacts differently when it strikes an 

object; it is reflected or absorbed by an 

object1 at different degrees. When a 

wavelength is reflected by an object, our 

eyes see the reflectance as a color associated 

with that wavelength. 

A piece of red cloth can be used as 

a further example. It will absorb most 

of the light that hits it, but because of 

the dye that was used it reflects the red 

wavelength that we see. Variations of red 

color are slightly different wavelengths 

or a combination of blue and green 

wavelengths that we see. A black shirt 

absorbs all of the light wavelengths and 

does not reflect anything (thus why a 

black shirt is hotter on a sunny day); a 

white shirt reflects all light wavelengths 

(why a white shirt is cooler). 

A digital camera will separate the colors 

into groups of wavelengths (also called 

“bands”) and a detector senses how 

much of each color has been reflected 

from the object, and thus an image is 

captured. 

The resolution of the image is what 

determines how detailed that image 

is. Resolution in cameras is commonly 

measured as “megapixels”. This is 

basically the number of detectors that 

the sensor has. Each detector captures 

the reflectance for one piece of the image 

(also known as a pixel). Higher quality 

sensor’s resolution is measured as 

“Ground Sample Distance” (GSD) which 

is a distance of ground that represented 

by one pixel. A GSD of 1 ft means the 

detector has captured the reflectance 

from a 1 ft X 1 ft area of the ground and 

is represented by one pixel. 

Digital cameras used in the majority 

of smaller drones are RGB cameras that 

result in the natural color imagery. This 

works for many users to see aerial imagery 

of a house or property, construction 

site, accident scene, crime scene, or 

utility lines. West Hills has several UAS 

with RGB cameras that are used for documenting 

a crop, field, or irrigation on 

the Farm of the Future. The resolution 

of 1–2 inches allow us to see individual 

plants, irrigation lines, and branch 

structure within our orchard trees. This 

is valuable for documenting what is in 

the field and some simple determination 

for management. But it doesn’t give us 

detailed data about the health or vigor of 

a plant for further analysis. 

Besides visible light wavelengths, 

there are also light wavelengths that 

are not visible to the naked human eye. 

The most common of these invisible 

wavelengths are: NIR (Near Infrared 

that is nearest to the red visible band); 

Mid-range IR (this is a wavelength that 

reflects thermal waves); and Far IR 

(this is infrared that is farther from the 

red visible band). They have their own 

reflectance properties, which means that 


even if the human eye cannot see them, a digital sensor can! 

Just like capturing red, green, or blue bands, a filter can be 

used to separate the infrared band and then captured by the 

detector. The value of capturing an NIR is the difference in its 

reflectance properties from plant tissue. 

• Green wavelengths reflect at a relatively high percent 

from healthy plant tissue, which why we see plants as green 

• Red wavelengths reflect at a relatively low percent and 

absorbed at a high percent from healthy plant tissue, be 

cause photosynthesis relies heavily on red light 

• Infrared wavelengths reflect at a significantly high percent 

from healthy plant tissue 

From this we can also say that red is reflected at a high percent 

from stressed or dead plant tissue, (which is why tree leaves 

turn red or other colors in the fall). Infrared will be absorbed 

by stressed or unhealthy plant tissue, meaning that less will 

be reflected. Capturing infrared reflectance allows the user to 

determine the stress level of plant tissue. The higher the reflectance, 

the less stress the plant is experiencing. 

There is a small problem; if infrared is invisible how do 

we see it? When we take a RGB image, the image is displayed 

using its respective color. How do we display an image that has 

no color? Most analysts will display the infrared band as red 

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31


which creates what is known as a false 

color image. All green vegetation is now 

displayed as red. And not just red, but 

the differences in shades of red are based 

on the stress level of the plant. Bright red 

is a healthy plant; pink or dirty red is a 

stressed plant. 

different set of wavelength bands. Users 

need to decide which bands are most 

appropriate for them. 

These are all high quality sensors, 

but since they are 400-500 miles above 

the earth, they are fairly low resolution. 

The GSD of most Landsat imagery is 10 

meters, much lower resolution than the 

two to three inches from a UAS. This 

Where do we get this multispec 

imagery from? If you have an unmanned 

aerial systems with a multispectral sensor 

you can capture your own imagery. 

However there are two other common 

and valuable platforms: satellite and 

manned flight. I taught a digital imagery 

course for years using Landsat satellite 

multispectral imagery. This imagery is 

FREE if you know how to find it, download 

it and process it. (This is beyond the 

scope of this article; come to West Hills 

College and take my Digital Imagery 

class!) 

There are seven Landsat satellites 

taking images of every part of the earth. 

The imagery is available for download 

in the form of seven separate bands of 

Blue, Green, Red, NIR, Mid-Range IR 

(Thermal), Far-Range IR, and depending 

on the Landsat another IR and or 

panchrometric (higher resolution black 

and white). Sensors used vary for each 

Landsat satellite and included: MultiSpec 

Scanners; Thematic Mapper; Enhanced 

Thematic Mappers; and Operational 

Land Imager. Each captures a slightly 

provides wide imagery over a field, but 

does not allow images of individual trees 

or plants. For large fields or farms, satellite 

imagery is good infrared data that 

can be converted to NDVI (Normalized 

Differential Vegetative Index) or other 

vegetative indices. 

Another problem with satellite imagery 

is that many times clouds are covering 

the earth surface. Most wavelengths 

that we want, do not pass through clouds 

and therefore the image is restricted. 

There are very short radar wavelengths 

that will pass through clouds, but they 

provide limited useful data. 

These concerns are addressed by the 

use of manned aerial flights. Missions 

can be flown at 1200 ft to 28,000 ft AGL 

(Above Ground Level) and at almost any 

time. Clouds can be avoided and a large 

area covered very quickly. Considering 

the area covered, the cost on a per acre 

basis is very reasonable. 

A professional aerial imagery service 

does not just stick a camera out the 

window. The sensor is a high quality 

multispectral camera mounted in an 

opening of the belly of the aircraft. The 

deliverables from the service could be 

the raw images if the customer has the 

means to do the processing or a final 

ortho-rectified and georeferenced image 

ready for interpretation. West Hills relies 

on GeoG2 Solutions, an aerial imagery 

service that provides us with monthly infrared 

images of our Farm of the Future 

for use in class. 

Though I introduced this topic saying 

that imagery is the important step, there 

is actually a lot more to remote sensing. 

There is also imagery processing software, 

spectral signatures, hypersprectral, 

radiance, and thermal bands that have 

importance to agriculture. Most of it 

is still being researched. Hopefully the 

background in this article has been helpful 

to continue forward when it becomes 

available. 

1. Actually there are four things that 

happen to light when it hits an object: 

transmitted, reflected, absorbed, refracted. 

For simplicity, reflected and 

absorbed are the two things we are most 

concerned about. 





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33

Location: 

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General Seminars 

08:00 | Almond Building 

The Burden of Compliance—Dealing with the Skyrocketing 

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Panel speakers: Roger Isom, Emily Rooney, Scott Mueller, Dan Errotabere, 

and Robert Gulack 

12:15 | Almond Building 

Navel Orangeworm Management—Current and 

Future Prospects 

Speaker: Brad Higbee, Field Research and Development Manager 

for Trécé Inc. 

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7:00 AM Registration 

7:30 AM 

Trade Show 

PCA-CE Credits: 15 minutes; Other 

8:00 AM The Burden of Compliance—Dealing with the Skyrocketing Costs of Compliance Proactively; 

Panel Speakers—Roger Isom, Emily Rooney, Scott Mueller, Dan Errotabere, and Robert Gulack 

(Almond, Walnut and Pistachio Combined Session To Be Held in Almond Building) 

8:30 AM How to Maximize Biological Control 

for Spider Mites in Almonds; 

David Haviland; UC Davis 

Entomology & Pest Management 

Farm Advisor; 

PCA-CE Credits: 30 minutes; 

Other 

Advances in Spray Application 

Technology for Precision Chemical 

Applications; 

Alireza Pourreza, UCCE Extension 

Advisor; 


Anthracnose; Is it a Threat to California 

Pistachios? 

Themis Michailides; Professor and 

Plant Pathologist at UC Davis; 


9:00 AM Management of Soilborne Diseases 

in Replanted Almond Orchards; 

Mohammad Yaghmour, UCCE Farm 

Advisor; 


Other 

9:30 AM FSMA Produce Safety 101 for 

Almond Growers; 

Tim Birmingham, Director, Quality 

Assurance & Industry Services, 

Almond Board of California 

Monitoring and Management of 

Walnuts Pests—Codling Moth, 

Husk Fly, and NOW; 

Charles Burks, USDA/ARS Research 

Entomologist; 


State of the Industry Update; 

Jennifer Williams and Claire Lee, 

California Walnut Board 

10:00 AM Break/ Trade Show 

Best Treatment Timings and 

Management of Large and Small 

Bugs in Pistachios; 

Kris Tollerup, UC Statewide IPM; 


State of the Industry Update; 

American Pistachio Growers; 

Richard Matoian, Executive Director 

10:30 AM Identification, Control, and Management 

of Ant Populations; 

Kris Tollerup, UC statewide IPM; 


Other 

11:00 AM Self-Compatibility: Is It Right for 

Your Orchard? 

Craig Ledbetter, Research Geneticist 

USDA/ARS 

The Latest in Spray Applications 

for Controlling Botryosphaeria; 

Themis Michailides, Professor and 

Plant Pathologist at UC Davis; 


Preplant Site Selection, Planning 

and Designing your Walnut 

Orchard; 

Mae Culumber, UCCE Farm Advisor 

Soilborne Diseases from Chemical 

Controls to Best Management Practices 

for Pistachios; 

Phoebe Gordon, UCCE Farm Advisor; 


Pistachio Rootstock Production and 

Selection; 

Elizabeth Fichtner, UCCE Farm 

Advisor 

11:30 AM Controlling Fungal and Bacterial 

Diseases in Almonds; 

Brent Holtz, UCCE Farm Advisor; 


Other 

New Chemistries for Weed Control 

Pre- and Post-Emergent; 

Kurt Hembree, UCCE Farm 

Advisor; 


12:00 PM - Free BBQ Tri-Tip Lunch 

The Latest on Winter Chill and How 

it Impacts Crop Prediction; 

Craig Kallsen, UCCE Farm Advisor; 


12:15 PM Navel Orangeworm Management—Current and Future Prospects; 

Brad Higbee, Field Research and Development Manager for Trécé Inc.; PCA-CE Credits: 30 minutes; Other 

1:00 PM 

Trade Show 


1:30 PM Adjourn 



35

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The Burden of Compliance—Dealing 

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Proactively 

Panel speakers: Roger Isom, Emily Rooney, Scott 

Mueller, Dan Errotabere, and Robert Gulack 

12:15 | Lunch Area 

Navel Orangeworm Management—Current 

and Future Prospects 

Speaker: Brad Higbee, Field Research and Development 

Manager for Trécé Inc. 

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Progressive Crop Consultant September/October 2017

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Registration For All Seminars Begins at 7:00 AM 

ALMOND SEMINARS WALNUT SEMINARS WORKSHOPS 

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7:00 AM Registraton 

7:30 AM Trade Show 


8:00 AM The Burden of Compliance—Dealing with the Skyrocketing Costs of Compliance Proactively; 

Panel Speakers—Roger Isom, Emily Rooney, Scott Mueller, Dan Errotabere, and Robert Gulack 

(Almond and Walnut Combined Session To Be Held in Workshop Area) 

8:30 AM Advances in Spray Application Technology 

for Precision Chemical Applications; 

Alireza Pourreza, UCCE Extension Advisor; 

CCA-CE Credits- Integrated Pest 

Mgmt: 30 Minutes 


9:00 AM Early Beehive Removal and Spray Timing 

Can Impact Pollination and Yield; 

Wes Asai, Pomology Consultant; 

CCA-CE Credits - Integrated Pest 



Managing Blight in Difficult Years: What 

Should be on Your Radar? 

Luke Milliron, UCCE Farm Advisor; 


Prevention and Management of 

Soilborne Diseases; 

Dani Lightle, UCCE Farm Advisor; 

CCA-CE Credits - Soil & Water Mgmt: 

10:00 

30 

AM 

Minutes 

Break/ Trade Show 


Improve Your Irrigation Management with 

a Pressure Chamber; 

Allan Fulton, UCCE Farm Advisor 

Essential Facts Every Grower Should Know 

Before Installing a New Well; 

Charlie Hoherd, Director of Sales & 

Marketing; Roscoe Moss Company 

9:30 AM FSMA Produce Safety 101 for Almond 

Growers; 

Tim Birmingham, Director, Quality Assurance 

& Industry Services, Almond Board of 

California 

State of the Industry Updates; 

Jennifer Williams and Claire Lee, 

California Walnut Board 

10:30 AM Five Key Components to Preventing 

Nitrogen Contamination of Groundwater; 

John Dickey Ph.D., CPSS, Agronomist, 

Soil Scientist; 

CCA-CE Credits - Nutrient Management: 30 

Minutes 

11:00 AM New Regulations for Spraying Near Schools 

and Day Cares; 

Marline Azevedo, Deputy Agricultural 

Commissioner—Pesticide Division, 

Stanislaus Agriculture Department; 



11:30 AM Managing Fungal and Bacterial Diseases in 

Almonds; 

Emily Symmes, UCCE Area IPM Advisor; 




10:00 AM Break/ Trade Show 

New Regulations for Spraying Near 

Schools and Day Cares; 

Marline Azevedo, Deputy Agricultural 

Commissioner—Pesticide Division, 

Stanislaus Agriculture Department; 



Five Key Components to Preventing 

Nitrogen Contamination of Groundwater; 

John Dickey Ph.D., CPSS, Agronomist, 

Soil Scientist; 

CCA-CE Credits - Nutrient Management: 

30 Minutes 

Advances in Spray Application Technology 

for Precision Chemical Applications; 

Alireza Pourreza, Assistant CE Advisor; 

CCA-CE Credits Integrated Pest 



12:00 PM - Free BBQ Tri-Tip Lunch 

Management Zone Based Precision 

Irrigation That Uses Leaf Monitors to Sense 

Plant Water Status and Improve Irrigation 

Efficiency; 

Shrinivasa Upadhyaya, Professor, UC Davis 

New Research is Developing a Soil App to 

Evaluate Nitrogen Leaching; 

Toby O’Geen, UCCE Extension Specialist 

Turning Ag Waste into Profit; 

Bill Ort, Research Leader USDA/ARS 

12:15 PM Navel Orangeworm Management—Current and Future Prospects; Brad Higbee, Field Research & Development Manager for Trécé Inc.; 

CCA-CE Credits - Integrated Pest Mgmt: 30 Mintues; PCA-CE Credits: 30 minutes 

(Almond and Walnut Combined Session To Be Held in Workshop Area) 

1:00 PM Trade Show 


1:30 PM Adjourn 



37


The fully irrigated baseline SWP for any given day and 

time is defined as the SWP that is expected if soil moisture 

is abundant and not limiting transpiration under the 

prevailing temperature and humidity conditions. Baseline 

may or may not vary with crop species. For example, 

baseline conditions for almond and prune are very similar 

but are different for walnut. Baseline values are derived 

from mathematical models and have been validated in field 

experiments in almond, prune, and walnut. 

Estimates of fully irrigated baseline SWP for almond 

and prune over a range of air temperatures and relative 

humidity are provided in Table 1 (pg. 10). Estimates of 

a fully irrigated baseline SWP for walnut are provided in 

Table 2 (pg. 10). During cool weather, estimates of baseline 

SWP may be –5 to –8 bars in almond and prune. However, 

under extremely hot and dry conditions, baseline SWP for 

almond and prune may be –11 to nearly -14 bars. In walnut, 

estimates of baseline SWP may be -3 to -5 bars during cool 

weather and -6.5 to near -8 bars during extremely hot, dry 

weather. 

Estimating baseline conditions requires access to public 

or private weather databases (e.g., CIMIS) that provide 

hourly temperature and relative humidity data, or an inexpensive, 

simple handheld instrument that can measure 

temperature and relative humidity in the orchard at the 

same time that SWP measurements are taken. 

An online calculator of baseline SWP is also available 

through the Fruit and Nut Research and Information Center: 

informatics. plantsciences.ucdavis.edu/Brooke_Jacobs/ 

index.php. Alternatively, go to the Fruit and Nut Center 

website (fruitsandnuts.ucdavis.edu), go to the “Weather 

Related Models” tab and select “Stem Water Potential”. 

Comparing orchard SWP measurements to fully irrigated 

baseline SWP estimates allows you to express your 

orchard’s SWP in bars below baseline. An example would be 

a day when weather is normal, the almond baseline is –10 

bars and the orchard SWP measurements average –14 bars, 

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or 4 bars below baseline. This suggests that tree water stress is 

occurring and that the need for irrigation is approaching. In contrast, 

on a different but very hot, windy day in the same almond 

orchard, when the baseline is –13 bars SWP and the orchard 

measurement averages -14 bars or just 1 bar below baseline, it 

suggests these readings are more associated with hot, dry weather 

conditions than with irrigation management. Once the hot, dry 

weather passes, both the estimate of baseline SWP and the orchard 

SWP measurements may recover to levels indicating lower 

tree stress. This information could guard against irrigating too 

soon or too much and help manage incidences of root and foliar 

diseases and improve access into the orchard for other activities. 

Other potential benefits of comparing fully irrigated baseline 

to the actual SWP measurements include identifying orchards 

that are steadily near or above the fully irrigated baseline the 

entire season. These orchards may be at more risk of eventual tree 

loss from excess water and resulting diseases. Comparisons between 

baseline and actual SWP measurements can also be helpful 

to dial-in regulated deficit irrigation strategies to better manage 

uniformity of crop development and maturation. Examples include 

more uniform hull split and harvest timing in almond and 

higher sugar content and lower “dry-away” in prune. Using baseline 

estimates may also enable earlier use of a pressure chamber 

and SWP in the spring when weather is more variable. 

Interpretive Guidelines for Almond, Prune, 

and Walnut 

Additional interpretive guidelines are provided in Tables 3, 4 

(pg. 40) , and 5 (pg. 42), for almond, prune, and walnut, respectively. 

They show that the ranges in SWP for almond and prune 

are similar up to a point. Almond may be able to survive more 

extreme levels of water stress than prune. However, research has 

not been conducted in prune to quantify how extreme water 

stress can become before mature trees no longer survive. Research 

has shown that walnut has a distinctly different range in 

water stress than almond or prune. 

In general, UC production research has shown the optimum 

range in crop water stress levels of about -6 to -18 bars for almond, 

-6 to -20 bars for prune, and -4 to -8 bars for walnut. Some 

production research indicates that exceptional production may be 

possible when irrigation is managed to maintain tree water status 

to minimize or completely avoid SWP stress levels for the entire 

season. However, university experiments and production experience 

supporting intensive irrigation management that sustains 

orchards near baseline and minimal tree stress throughout the 

season is not conclusive. Concern exists about higher incidence 

of root and foliar diseases, lower limb shading and dieback, and 

shortened orchard life. Orchards, where SWP fluctuates more 

within these optimum ranges may still yield competitively but 

incur less tree loss and produce longer. 

SWP is a field diagnostic tool that can help growers and consultants 

understand short and long term trends in orchard water 

status. With this knowledge they can tailor their management 

to achieve specific objectives and goals which may be different 

between orchards due to different growing environments and 

orchard designs (i.e. cultivar and rootstock choices, planting 

configurations, and pruning practices). The pressure chamber 


and SWP may also assist with minimizing 

the impacts of short water supplies 

during drought and balance water and 

energy costs. 

Using SWP in other crops 

A grower or consultant who invests 

in a pressure chamber may be interested 

in its application in other crops. Research 

and development of the pressure 

chamber to evaluate crop water stress 

and help with on-farm water management 

has been undertaken in several 

crops for many decades. It’s readiness for 

on-farm use varies among crops. Cotton 

and wine grapes are examples of crops 

where an abundance of research has 

been conducted and information extended 

so the pressure chamber is available 

as a water management tool. However, 

in both of these crops the measurement 

technique differs from SWP. In these 

crops with smaller canopies, the sample 

leaf is not covered with a bag and leaf 

water potential is measured not SWP. 

In crops such as olive, pistachio, 

peach, pecan, seed alfalfa, and others 

there is limited information available. 

The information may originate both 

from California and other areas of the 

U.S. and internationally and may involve 

different sampling techniques other than 

SWP such as leaf water potential and 

shaded leaf water potential. If interested 

in any of these crops, one suggested 

source to begin a literature search is: 

https://www.pmsinstrument.com/research/. 

A Stand-Alone or Complementary 

Irrigation Management Tool 

As a direct measure of tree response 

to irrigation management and the soil, 

climate, and orchard environment, SWP 

is unique compared with other methods 

that assess tree water status indirectly. 

As such, through trial and error, SWP 

can be used—and has been successfully 

adopted by many growers—as a standalone 

technique for irrigation schedul- 


Table 3. SWP levels in almond, consideration of how SWP might compare to baseline values under typical weather conditions, and 

the corresponding water stress symptoms to expect. 

SWP range 

(bars) 

General 

Stress Level 

Baseline 

consideration 

-2 to -6 None (Likely above typical 

baseline) 

-6 to -10 Minimal At or within 2 bars below 

baseline under normal 

conditions 

-10 to -12 Mild Near baseline under hot, 

dry conditions, but 2 to 4 

bars below baseline under 

normal or cooler weather 

-12 to -14 Mild to 

Moderate 

-14 to -18 Moderate to 

High 

Within 2 bars below 

baseline under hot, dry 

conditions, and 4 to 6 

bars below baseline under 

normal or cool conditions 

Likely 4 to 5 bars below 


conditions and 6 to 8 bars 

below baseline in normal 

or cooler weather. 

-18 to -22 High Within 8 to 14 bars below 

baseline 

-22 to -30 Very High Within 14 to 24 bars 

below baseline 

-30 to -60 Severe Within 24 to 50 bars 


Below -60 

bars 

Extreme 

(Substantially below baseline 

under all conditions) 

Water stress symptoms in almond 

(Not commonly observed) 

Typical from leaf-out through mid-June. Stimulates shoot 

growth, especially in developing orchards. Higher yield 

potential may be possible if these levels are sustained (if the 

only limiting factor). Sustaining these levels may result in 

higher incidence of disease and reduced life span. 

These levels of stress may be appropriate during the phase 

of growth just before the onset of hull split (late June). 

Reduced growth in young trees and shoot extension in 

mature trees. Suitable in late June up to the onset of hull 

split (July). Still produce competitively. Recommended level 

after harvest. May reduce energy costs or help cope with 

drought conditions. 

Stops shoot growth in young orchards. Mature almonds can 

tolerate this level during hull split (July) and still yield competitively. 

May help control diseases such as hull rot and 

alternaria leaf spot, if present. May expedite hull split and 

lead to more uniform nut maturity. Also may help reduce 

energy costs and cope with drought conditions. 

Slow to no growth in mature orchards. Interior leaf yellowing 

with some leaf drop. Should be avoided for extended 

periods. Likely to reduce yield potential. 

Wilting observed. Stomatal conductance of CO2 and 

photosynthesis declines as much as 50% and impacts yield 

potential. Some limb dieback. 

Extensive or complete defoliation is common. Trees may 

survive despite severe defoliation. Severely reduced or no 

bloom and very low yield expected following one to two 

seasons until trees are rejuvenated. 

(Trees are probably dead or dying) 



39


ing. Using SWP alone, along with the 

interpretive guidelines presented in this 

article, gives relatively straightforward 

insights to the question of when to irrigate 

and with experience, perhaps how 

long to irrigate. 

However, trial and error may not 

suffice in some situations, and SWP 

measurements alone may not provide 

enough information. For example, pressure 

chamber measurements can show 

low crop stress in April, May, and early 

June in orchards, even though irrigation 

has been postponed or reduced. 

The trees consume water stored in the 

root zone from winter rainfall or winter 

irrigation during this period to satisfy 

their water requirements. Without some 

monitoring of soil moisture or tracking 

of ET, it is possible to experience a 

sudden and rapid increase in tree water 

stress in July, August, and September. 

Meanwhile, a drip or microsprinkler irrigation 

system will not have the capacity 

to apply enough water to recharge the 

soil moisture depletion and sufficiently 

relieve tree stress. This can be a problem 

particularly in orchards where soils have 

slow water infiltration. Irrigation should 

be initiated before the stored water is 

depleted excessively. 

Using SWP in conjunction with soil 

moisture monitoring or a water budget 

(or both) can also help overcome some 

common limitations of soil moisture 

monitoring and irrigating according to 

ET. SWP readings that indicate low tree 

stress, even though soil moisture sensors 

indicate dry soil, might suggest that trees 

are getting water from greater depths in 

the root zone that are not being monitored 

by soil moisture sensors. This situation 

could indicate a need for deeper 

soil moisture monitoring or placing soil 

moisture sensors in more representative 

locations. Similarly, SWP readings that 

indicate desirable levels of tree stress, 

even when a water budget indicates 

under-irrigation, suggest the need to 

reexamine assumptions about ET rates, 

rooting depth, and available moisture 

reserves. 

In a different situation, SWP mea- 


SWP range 

(bars) 

General 

Stress Level 

Baseline 

consideration 


-2 to -6 None (Likely above typical 

baseline) 

-6 to -8 Minimal At or near baseline 

under normal or cool 

weather conditions 

-8 to -12 Minimal to 

Mild 

-12 to -16 Mild to Moderate 

-16 to -20 Moderate to 

High 

At or near baseline under 

hot, dry conditions, 

but may be 2 to 4 bars 

below baseline under 

normal or cool conditions 

May be 2 to 4 bars below 

baseline under hot, 

dry conditions, but may 

be 4 to 6 bars below 

baseline under normal or 

cooler weather 

Within 6 to 8 bars below 

baseline 

-20 to -30 High to Severe Within 8 to 20 bars 


Below -30 Extreme (Substantially below 

baseline under all conditions) 


Typical in March and April. Indicates soil moisture is not 

limiting. If sustained, higher incidence of root and foliar 

diseases and tree loss may occur. 

Favors rapid shoot growth and fruit sizing in orchards 

when minimal crop stress is sustained from April through 

mid-June. 

Suggested mild levels of stress during late June, July, and 

early August. Shoot growth slowed but fruit sizing unaffected. 

May help manage energy and irrigation costs. 

Should be avoided until fruit sizing is completed. Appropriate 

for late August after fruit sizing is completed. Imposing 

moderate to high levels of crop stress by reducing irrigation 

about two weeks before harvest may increase sugar 

content in fruit and reduce moisture content or “dry-away” 

(fruit drying costs). 

More likely to occur in late August and early September 

during and after harvest. Extended periods of high crop 

stress before harvest will result in defoliation and exposure 

of limbs and fruit to sunburn. Extended periods of high 

stress after harvest may also negatively affect the condition 

of trees going into dormancy. 

Extended periods of severe crop stress should be avoided. 

Trees will defoliate and be exposed to sunburn, increasing 

the risk of canker diseases. Potentially shorten productive 

life of orchard. 

Table 4. SWP levels in prune, consideration of how SWP might compare to baseline values under various weather conditions, and 

the corresponding water stress symptoms to expect. 


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September/October 2017 www.progressivecrop.com 41

SWP range 

(bars) 

General 

Stress Level 

Baseline 

consideration 


Higher than 

–2 

None 

(Likely above typical 

baseline) 

-2 to –4 None At or above typical 

baseline 

-4 to –6 Minimal May equal or be as much 

as 2 bars below typical 

baseline 

-6 to –8 Mild May equal baseline 

under hot, dry conditions, 

but may be 2 to 4 bars 


-8 to –10 Moderate May be 1 to 2 bars 


hot, dry conditions but 4 

to 6 bars below baseline 

under normal or cooler 

weather 

-10 to –12 High Likely 3 to 4 bars below 


conditions and 6 to 8 

bars below baseline in 

normal or cooler weather. 

-12 to –14 Very High Likely 5 to 6 bars below 





-14 to –18 Severe Likely 7 to 8 bars below 





Below -18 Extreme (Substantially below baseline 

under all conditions) 


Fully irrigated. Commonly observed when orchards are irrigated 

according to estimates of real-time evapotranspiration 

(ETc). If sustained, long term root and tree health may 

be a concern, especially on California Black rootstock 

High rate of shoot growth visible, suggested level from leafout 

until mid-June when nut sizing is completed 

Shoot growth in non-bearing and bearing trees has been 

observed to decline. These levels do not appear to affect 

kernel development or quality. 

Shoot growth in non-bearing trees may stop, nut sizing may 

be reduced in bearing trees and bud development for next 

season may be negatively affected. 

Temporary wilting of leaves and shrivel of hulls has been 

observed. New shoot growth may be sparse or absent and 

some defoliation may be evident. If sustained, nut size will 

likely be reduced with darker kernel color. 

Results in moderate defoliation. Should be avoided. 

Severe defoliation, trees are likely dying. 

(Trees are probably dead or dying) 

Table 5. SWP levels in walnut, consideration of how SWP might compare to baseline values under various weather conditions, 

and the corresponding water stress symptoms to expect. 


surements might indicate moderate to 

high tree stress even when soil moisture 

sensors placed within the wetted pattern 

of the drip emitter show high soil 

moisture content. In this case, additional 

investigation is necessary to determine if 

roots are healthy and growing, and if the 

soil moisture sensors accurately represent 

the root zone and predominant soil 

types or if the sensors are defective. 

Acknowledgements 

Numerous (too many to mention 

all) University of California faculty and 

students, extension specialists and farm 

advisors have invested years of field 

research to develop the pressure chamber 

and midday stem water potential as 

a viable on-farm water management tool 

for almond, prune, and walnut. This 

article would not be possible without 

their contributions and seeks to capture 

all of the experience as accurately and 

concisely as possible. Special thanks to 

Ken Shackel, Bruce Lampinen, and Sam 

Metcalf of UC Davis Department of 

Plant Sciences for their career long commitment 

to seeing the pressure chamber 

and midday stem water developed into a 

valuable water management tool. 





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with Willowood USA post-patent crop 

protection products. Containing the 

same active ingredients as namebrand 

products, our line of fungicides, 

insecticides, herbicides and plant 

growth regulators gives you a broad 

spectrum of protection and the kind 

of value you can’t get anywhere else. 

For tree fruit and nuts, Willowood 

has the solutions you need at a 

price you can’t beat. 

Contact your local 

ag retailer or visit 

WillowoodUSA.com 

to learn more. 

Same active as GOALTENDER. ® Same active as GRAMOXONE. ® 

Same active as ADMIRE PRO. ® 

Same active as SELECT. ® Same active as RELY. ® 

Same active as GOAL. ® 

Same active as AGRI-MEK. ® Same active as AGRI-MEK SC. ® Same active as ACRAMITE 50W. ® 

Same active as ABOUND. ® 

Same active as ELITE. ® 

Always read and follow label directions. ©2017 Willowood USA. All Rights Reserved. ABOUND and 

GRAMOXONE are registered trademarks of a Syngenta Group Company. GOAL and GOALTENDER are 

registered trademarks of Dow AgroSciences. RELY, ADMIRE PRO and ELITE are registered trademarks 

of Bayer CropScience. SELECT is a registered trademark of Valent. Agri-Mek and Agri-Mek SC are 

registered trademarks of Syngenta. Acramite 50W is a registered trademark of Arysta LifeScience.

September/October 2017

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