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TAKE UC RESEARCH INTO CONSIDERATION. We spend a lot of dirty days and long
nights collecting, analyzing, and preparing inspiring PowerPoint presentations to tell you the
results of properly randomized and replicated experiments conducted by academically
talented people. For example, let's review the Regulated Deficit Irrigation (RDI) research
designed and led by now-retired Dr. David Goldhamer, a UC Extension Specialist in the
Land, Air, and Water Resources Department at UC Davis, but stationed at the UC Kearney
Field Station (I get to call it the original name because I am old!). Dave was THE original
researcher on pistachio water use. I had the pleasure of working with him for 25 of my 35
years in Extension. When we first started studying pistachio irrigation, many claimed its water
requirement was only 24 inches. "I don’t believe that," Dave stated. "Let's find out!" So began
three decades of water research, making pistachios the best prepared nut crop for coping
with drought years. Included in these experiments were studies on PURPOSELY withholding
water during one or more of the three crop development periods: Stage 1= bud break to late
May when the shells had fully expanded and partially hardened; Stage 2= late May to late
June when shell hardening and shoot growth continues; Stage 3= late June to harvest when
kernel filling (as well as final shell hardening) occurs. Our first RDI research produced the
following results: |
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"Effect of Regulated Deficit Irrigation at Stages 1, 2, and 3 on pistachio nut quality and yield." |
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We discovered the following KEY POINTS: |
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A. |
Withholding water during Stage 1 REDUCED nut size, INCREASED SPLITTING, and
DID NOT affect nut removal at harvest. It DID NOT affect blanking or nut abortion. Yield
was unaffected. |
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B. |
Stage 2 water stress DID NOT significantly reduce nut size; split percentages were
DECREASED, nut removal was INCREASED, blanking and aborted nuts were NOT
affected, and filled nut yield was reduced, but not significantly so. |
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C. |
Stage 3 water stress DECREASED nut weight, NOT because of smaller shell size, but
because the kernels did not fill the shell completely to split it open. Water stress during
Stage 3 also INCREASED nut abortion and dramatically REDUCED split percentages;
split nut yield at harvest was only ONE-THIRD of the well-watered trees. The yield of
filled nuts was also significantly reduced. Nut removal also DECREASED. |
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These results prompted a second RDI experiment to confirm and refine this concept as a
useful grower tool: |
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"Effect of RDI on pistachio nut quality and yield grown on P.atlantica and P.integerrima." T1=
Stage 1 stress (18 bars by late May) followed by full ETc. T2= Stage 1 water stress followed
by 50% of potential ETc during Stage 2. The Control was irrigated using real time CIMIS data
to meet full ETc. |
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This experiment confirmed the results of the first and showed that we could use RDI to
reduce applied water by as much as 12 inches without adversely affecting blank or aborted
nuts, nut removal or split nut yield. However, water stress during Stage 1 does DECREASE
nut size and there is limited research to suggest that it increases early pea split nuts, which is
a major concern for navel orangeworm (NOW). NOW adults transition from overwintering
mummy nuts to the early pea splits in July to increase their population as harvest
approaches. |
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UC research also shows that the improvement in split percentage is NOT associated with
water stress during Stage 2, but rather Stage 1 by reducing the nut size slightly. Reduced nut
size allows the rapidly developing kernel under full ETc in Stage 3 to split the shell. Note that
the T2 treatment in which water stress was CONTINUED at 50% of ETc during Stage 2 had
the same split nut yield at harvest as the trees experiencing water stress during Stage 1.
Recent UC research shows that shell hardening is only about 45% complete by July 1. The
fact that over half of shell’s lignification occurs under full ETc in Stage 3 reduces the likelihood
that Stage 2 water stress contributes to improved shell splitting. More research is needed on
this subject. |
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I have provided you with this historical data to show you how CRITICAL it is to maintain
well-watered conditions during Stage 3 (kernel filling). Simply applying the required amount of
water is NOT sufficient. You must verify that the water is infiltrating the soil and the leaves are
cool to the touch if you cannot measure Stem Water Potential (SWP) using a pressure
chamber. I have recently had farm calls regarding trees appearing to be water-stressed, but
water is STANDING next to the trees. So, I dam up a circle of soil near an emitter, bail out the
surface mud, and auger a hole. I typically find the soil extremely dry at 12-18 inches! August
is too late to surface-apply gypsum, in my opinion; it can become a worker safety issue
during harvest if the treated area does not get fully wetted. You can apply solution grade gyp
through your drip system, but the amount must be 500 POUNDS of solution gyp per
acre-foot of water applied! That amount increases the milliequivalents of soluble calcium in
the water to 2.0, which is the minimum required to improve infiltration, based on research
performed by retired UC Farm Advisor, Allan Fulton, during his tenure in Kings County. The
other option for poor infiltration near harvest is calcium thiosulfate. It's expensive, but it's easy
to apply, and 20-30 gallons per acre may be needed to make significant improvement in
some soils. Consult your PCA or crop advisor on rates based upon your soil chemistry.
Bicarbonates play a big role in reducing the effectiveness of calcium application, so you need
relatively current soil and water analyses to help guide your infiltration correction program. |
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Discuss your NOW program with your crop advisor. Monitor your orchard for the
abundance of early pea splits. Perform a timed search for these nuts that provide NOW the
needed bridge between the old mummies and new crop. Collect as many early pea splits as
you can find in five minutes. Five or less is a low number; 25 is high. Get out your hand lens
and look for NOW eggs laid on the split area exposing the tiny nut. Then crack out the nut
and look for frass, tiny pin holes, or small worms. If you do not know how to identify the
various stages of NOW development, go online to the UC IPM pistachio website and look at
the photos. You should also join your crop consultant during their survey to learn what to look
for. Most pistachios get treated for NOW in early August at the beginning of the third
generation. Talk to your advisor soon about what materials he plans to use and get them
ordered and waiting for treatment. Be sure to spray ON TIME! A week after your advisor
recommends treatment is NOT ON TIME! This is the single greatest ulcer-producing issue
with crop advisors; growers get the recommendation, don’t respond quickly, and then
complain that they missed out on the premiums because of excess NOW! Crop development
appears to be delayed about 10 days, so keep this in mind in timing your treatments. |
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Harvest promptly! Don't wait for the hulls of Golden Hills to start tattering! Beginning about
August 7, randomly collect 20 clusters in a five-gallon bucket. Strip all the nuts off the rachis,
and then attempt to peel the nut by squeezing it between your thumb and index finger. Place
those that peel in one pile, and those that do not in another. Then cut the non-peelers in half
to see if they are filling or blank; place those that are filling in one pile, and the blanks in
another. Determine the "slip percentage" for that date by dividing those that peeled by the
SUM of the peeled and non-peeled but filling. DO NOT include the blank nuts! They will
never slip! If you follow this procedure, you will LEARN how fast your nuts are maturing, and
be able to accurately decide your harvest date. Once you reach 95% slip, you should pull the
harvest trigger. Keep monitoring hull condition and temperatures to learn how fast hull
breakdown occurs for future reference! Kerman can tolerate more hull tattering than Golden
Hills before staining becomes an issue. |
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Watch out for late-season large plant bugs, such as stink and leaf-footed bugs. Most crop
advisors add a pyrethroid to the August NOW spray for adult knockdown and plant bugs. |
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Get your leaf samples taken. August is the preferred timing for pistachio tissue analysis
since the critical values are based on this time period. This allows you to prepare for
post-harvest nutrient management. Soil samples need to be taken as well to determine your
nitrogen, boron, phosphorous and potassium reserves. They will also help diagnose other
possible deficiencies, such as magnesium. |
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Finish budding newly planted trees. Budding should be completed by August 10, in my
opinion, if you are going to have a good chance of getting the scion up the stake to at least
48 inches. Bud the rootstock at least 28 inches off the ground so you only need 20 inches of
scion growth to get it to the top of the stake. You REALLY have to pay attention to late
budded fields to drive the scion growth!! Competing rootstock and scion laterals must be
suppressed by clipping or pinching their tips to force all the growth into the shoot being
trained up the stake! If you do the math, it takes 14 days for the new bud to push, so trees
budded on the 10th are now pushing on the 24th. The buds can grow an inch per day under
well-managed conditions, so it’s possible to have the scion at the top of the stake by the end
of September. However, you CANNOT keep watering newly budded trees until late
September in soils whose texture is loam or greater! They have too much water holding
capacity, and the trees can very likely be green and tender at the end of October. This
predisposes them to freeze injury, which can KILL the scion ALL THE WAY BACK TO THE
ROOTSTOCK! Carl Fanucchi cuts newly budded trees off in AUGUST in many cases
because there is plenty of water in the Kern County heavier soil textures to supply growth.
The latest I would LIGHTLY water a SANDY-TEXTURED soil is the 10th of September.
Driving growth after budding with nitrogen is a recipe for DISASTER! |
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Happy Farming! |
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