September/October 2017

jcsmarketinginc10

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,

UCCE Kern County

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

September/October 2017

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.

4 Progressive Crop Consultant September/October 2017


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

September/October 2017

www.progressivecrop.com

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

in an orchard?

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

growing on one predominant soil type

with uniform irrigation. More trees

Continued on Page 8

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Continued from Page 6

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.

8 Progressive Crop Consultant September/October 2017


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.

Continued on Page 38

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

Continued from Page 9

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

10 Progressive Crop Consultant September/October 2017


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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.

12 Progressive Crop Consultant September/October 2017


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

Continued on Page 14

September/October 2017

www.progressivecrop.com

13


Continued from Page 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

Wilted 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

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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

14 Progressive Crop Consultant September/October 2017


Symptoms Macrophomina Fusarium Phytophthora

Older leaves affected first Yes Yes Yes

Gray green foliage Yes Yes Yes

Wilted leaves 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

September/October 2017

www.progressivecrop.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

Continued on Page 18

16 Progressive Crop Consultant September/October 2017


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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

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18 Progressive Crop Consultant September/October 2017


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

Continued on Page 20

Unfumigated (Foreground) Chloropicrin fumigated

(Background)

September/October 2017

www.progressivecrop.com

19


Continued from Page 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).

20 Progressive Crop Consultant September/October 2017


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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September/October 2017

www.progressivecrop.com

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

22 Progressive Crop Consultant September/October 2017


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.

Comments about this article? We want

to hear from you. Feel free to email us at

article@jcsmarketinginc.com

September/October 2017

www.progressivecrop.com

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

Continued on Page 26

24 Progressive Crop Consultant September/October 2017


PUT YOUR ALMONDS

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RIGHT NUTRITION.

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Apply High Phos as Part of Your Post Harvest Fertilizer Program.

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For more information visit wrtag.com, or

contact Joseph Witzke at (209) 720-8040

September/October 2017

www.progressivecrop.com

25


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

Continued from Page 24

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).

26 Progressive Crop Consultant September/October 2017


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

UCCE Kern County

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

UCCE Kern County

1031 South Mount Vernon Avenue

Bakersfield, CA 93307, USA

(661) 868-6221

blsanden@ucdavis.edu

Comments about this article? We want

to hear from you. Feel free to email us at

article@jcsmarketinginc.com

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.

September/October 2017

www.progressivecrop.com

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-

Continued on Page 30

28 Progressive Crop Consultant September/October 2017


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ROOT HEALTH & TREE LONGEVITY THREAT

GROWERS CAN’T SEE

UNSEEN BUT

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Nematodes, microscopic roundworms barely visible to the naked eye,

pose a serious problem for walnut and almond growers. Even with proper

sanitation and fumigation practices, nematodes can still become an issue

after setting new trees. Nematode populations can build up in the soil,

attack tree roots and impact overall tree health.

NEMATODE

THREATS TO

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HEALTH AND

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IN YOUNG TREES

BEST PRACTICES FOR

TREATING NEMATODES 3

1. Sample for nematodes to determine the

presence, species and number of nematodes

through an experienced lab.

2.

3.

If possible, fumigate the soil prior to planting

new trees. This will reduce the number of

nematodes initially, but will offer only a

temporary solution.

Applications of Movento ® in established orchards

resulted in a reduction of nematode populations.

Movento does offer a nematode management

tool that can easily be incorporated into a tree

nut grower’s cultural practices.

Two-year trials show

MOVENTO ® SUPPRESSES RING NEMATODES BY 85%

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Applications of Movento ® in established

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2,400

2,000

1,600

1,200

800

400

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EXPERTS SAY

“Established orchards saw better yield where Movento ®

was used to treat for high nematode pressure. The tree

has a lot of vigor and doesn’t stress as bad.”

According to Tim Weststeyn, a pest control advisor (PCA) with Crop Production Services

in Vernalis, CA. He consults on 4,000 to 5,000 acres of tree nuts and is in his third year of

treating established almond trees with Movento for nematode management. 4

1

Average yield loss in lbs. per acre is based on California Agricultural Statistics Review, 2014–2015. California Department

of Food and Agriculture.

2

“Nematodes: A Threat to Sustainability of Agriculture,” Satyandra Singh, Bijendra Singh and A.P. Singh.

3

University of California – Cooperative Extension. Department of Agriculture and Resource Economics. UC Davis, 2012.

4

“The Dangers of Nematodes,” Growing Produce – 2012.

LEARN MORE AT MOVENTO.US.

© 2017 Bayer CropScience LP, 2 TW Alexander Drive, Research Triangle Park, NC 27709. Bayer, the Bayer Cross, and Movento are registered trademarks of Bayer. Always read

and follow label instructions. Not all products are registered for use in every state. For additional product information, call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our

website at www.CropScience.Bayer.us.

September/October 2017

www.progressivecrop.com

29


Continued from Page 28

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

30 Progressive Crop Consultant September/October 2017


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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Continued on Page 32

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Info@westernnutrientscorp.com

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September/October 2017

www.progressivecrop.com

31


Continued from Page 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.

Comments about this article? We want

to hear from you. Feel free to email us at

article@jcsmarketinginc.com

32 Progressive Crop Consultant September/October 2017


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PCA-CE Credits: 30 minutes;

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9:30 AM FSMA Produce Safety 101 for

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Tim Birmingham, Director, Quality

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Almond Board of California

Monitoring and Management of

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Charles Burks, USDA/ARS Research

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State of the Industry Update;

Jennifer Williams and Claire Lee,

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10:00 AM Break/ Trade Show

Best Treatment Timings and

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Kris Tollerup, UC Statewide IPM;

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State of the Industry Update;

American Pistachio Growers;

Richard Matoian, Executive Director

10:30 AM Identification, Control, and Management

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Craig Ledbetter, Research Geneticist

USDA/ARS

The Latest in Spray Applications

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Themis Michailides, Professor and

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PCA-CE Credits: 30 minutes; Other

Preplant Site Selection, Planning

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Mae Culumber, UCCE Farm Advisor

Soilborne Diseases from Chemical

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for Pistachios;

Phoebe Gordon, UCCE Farm Advisor;

PCA-CE Credits: 30 minutes; Other

Pistachio Rootstock Production and

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Elizabeth Fichtner, UCCE Farm

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11:30 AM Controlling Fungal and Bacterial

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Brent Holtz, UCCE Farm Advisor;

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New Chemistries for Weed Control

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The Latest on Winter Chill and How

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Craig Kallsen, UCCE Farm Advisor;

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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

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CE Credits

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CCA: 4 Hours

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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

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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 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

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9:00 AM Early Beehive Removal and Spray Timing

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Managing Blight in Difficult Years: What

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Prevention and Management of

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Dani Lightle, UCCE Farm Advisor;

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Allan Fulton, UCCE Farm Advisor

Essential Facts Every Grower Should Know

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Charlie Hoherd, Director of Sales &

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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

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John Dickey Ph.D., CPSS, Agronomist,

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Marline Azevedo, Deputy Agricultural

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Mgmt: 30 Minutes

11:30 AM Managing Fungal and Bacterial Diseases in

Almonds;

Emily Symmes, UCCE Area IPM Advisor;

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Mgmt: 30 Minutes

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Marline Azevedo, Deputy Agricultural

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Stanislaus Agriculture Department;

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Mgmt: 30 Minutes

Five Key Components to Preventing

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John Dickey Ph.D., CPSS, Agronomist,

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Advances in Spray Application Technology

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Alireza Pourreza, Assistant CE Advisor;

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12:00 PM - Free BBQ Tri-Tip Lunch

Management Zone Based Precision

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

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www.progressivecrop.com

37


Continued from Page 10

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,

Scientifically proven to reduce

female NOW populations and

damage with Mass Trapping

and Monitoring.

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

38 Progressive Crop Consultant September/October 2017


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-

Continued on Page 40

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

baseline under hot, dry

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 baseline

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)

September/October 2017

www.progressivecrop.com

39


Continued from Page 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-

Continued on Page 42

SWP range

(bars)

General

Stress Level

Baseline

consideration

Water stress symptoms in almond

-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 baseline

Below -30 Extreme (Substantially below

baseline under all conditions)

(Not commonly observed)

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.

40 Progressive Crop Consultant September/October 2017


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information, call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our website at www.CropScience.Bayer.us.

September/October 2017 www.progressivecrop.com 41


SWP range

(bars)

General

Stress Level

Baseline

consideration

Water stress symptoms in almond

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

below baseline under

-8 to –10 Moderate May be 1 to 2 bars

below baseline under

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

baseline under hot, dry

conditions and 6 to 8

bars below baseline in

normal or cooler weather.

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

baseline under hot, dry

conditions and 8 to 10

bars below baseline in

normal or cooler weather.

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

baseline under hot, dry

conditions and 10 to 12

bars below baseline in

normal or cooler weather.

Below -18 Extreme (Substantially below baseline

under all conditions)

(Not commonly observed)

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.

Continued from Page 40

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.

Comments about this article? We want

to hear from you. Feel free to email us at

article@jcsmarketinginc.com

42 Progressive Crop Consultant September/October 2017


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