Pistachio Production

April 2015 Task List for Pistachios

By Bob Beede, University of California Cooperative Extension farm advisor, Emeritus, in Hanford

Field Observations: I went to Kern County to look at oiled and non-oiled pistachios with my good buddy, Carl Fanucchi, on March 12 and 19. Much of this effort was to gain personal knowledge of how oiling in mid- to late-January is performing.

Carl has supported this timing for many years, but there has never been a replicated trial done to confirm its performance. I have also never seen any bud push and bloom rating reports from growers or PCAs in the area that compared treated and non-treated trees. UC is all about having replicated data to support its educational program. The reasons for this are hopefully obvious to you, even though you believe the Coffee Shop Trials more than you do ours!

In our day-long tours from Tejon to Buttonwillow, nine year-old oiled Kerman trees, rated March 19 in Buttonwillow, were already at 60 percent early leaf out , 10-15 percent bloom, and 15-20 percent post-bloom. The oiled Peters males showed 5-10 percent bloom, and 25-30 percent pre-bloom. This orchard was oiled January 20, 2015. Unoiled Kerman trees in the same orchard were at 3-5 percent early leaf out, and 30-50 percent flower bud swell. The unoiled Peters showed about 50 percent flower bud swell, and only about 30 percent green tip.

In contrast, eight year-old Kermans, only a couple miles away, that were treated January 10 were rated 30 percent early leaf out, 70 percent green tip, and 50 percent bloom, but there was hardly any bloom to rate. The unoiled Kermans were 95 percent tight, 5 percent green tip, 50 percent tight flower buds, and 50 percent flower bud swell. The unoiled males had 100 percent tight vegetative buds; 70 percent of the flower buds were swollen but not approaching the pre-bloom stage.

So, it would certainly appear that January oil treatments work in this region, and it certainly indicates that a REPLICATED research project testing oil treatment timings from January 10 to February 10 is needed. It would also be good to perform this trial in the Buttonwillow area, as well as the Tejon area, since these two locations can receive different chill portions.

Although our efforts to substantiate oil response this year are commendable, it is nothing more than anecdotal data. However, it would certainly suggest that January treatments provide the same response we have observed with February treatments in the Kings, Fresno, and Madera areas. The big question now is whether or not the erratic winter weather patterns have also changed the treatment timing for the mid-valley area. Observations on the Westside Friday, March 20, suggest February can still be good for our area. I saw a nine-year-old block in a warm area north of Kettleman City that was treated February 10, and it was at 30 percent post bloom! The Peters males were just beginning to bloom, however. With low chill winters more common, refining the effect of oil application has become a high research priority, in my opinion.

It is also interesting to note that this block north of Kettleman, which showed such uniform and advanced leaf out from a February 10 oil treatment, was sprayed with the new TXD nozzle technology. The trees looked awfully good, suggesting another research project comparing conventional and TXD nozzles! Rest-breaking uniformity appears to be an excellent coverage assessment tool.

Spring Diseases: With the severe drought, we can only hope that it rains during bloom. If it does, it may be necessary to apply a fungicide to control Botrytis and Botryosphaeria. The potential for these diseases depends upon past infection levels and repeated rain events. Dr. Themis Michailides has determined 0.2 inches of rain and temperatures at or above 550 F constitutes a Botryosphaeria infection event. Your inoculum pressure can still be assessed by examining the base of old cluster rachises for blackened tissue, which extends into the one-year-old wood and looks like verticillium streaking from where the cluster attached to the branch. Infected old clusters also tend not to break cleanly from the shoot. Instead, they leave a stub, when one attempts to knock them off. Also examine older wood for sunken areas, which, when cut into, also have blackened tissue running lengthwise in the limb. These represent old infections, which can possess active pycnidia for up to six years. Botrytis attacks the male bloom more than the female, because the tufts of pollen are high in sugar and proteins, both good substrates for the growth of this fungus. Male cultivars 02-16 and 02-18 (old selections originally released with Peters to assist in its overlap of Kerman) are more susceptible than Peters due to their denser bloom character. Kerman female trees show Botrytis infection in young, tender shoots. Diseased shoots wilt, and their tips curl like a shepherd’s hook. They turn a dark dull green, not black! The base of the shoot also develops a cluster of buff-colored spores. Botryosphaeria shoot infections do not occur until later in the summer when it gets hot.

See pages 37-40 of your BOT manual to contrast Botrytis to BOT. Several fungicides are now registered and effective against these diseases. Consider the likelihood of treating for Alternaria later in the season, and save the fungicide most effective against Alternaria for use in June or July. You can compare fungicide efficacy (we still are waiting on the 2014 edition of this publication) at the UC website: http://www.ipm.ucdavis.edu/PDF/PMG/fungicideefficacytiming.pdf. Management of Alternaria resistance has now become a major concern for PCA’s and growers.

Water: You have heard the bad news; the worst snowpack in 100 years. It is only 12 percent of average. It was good that the Central Valley Project sent some water into the San Luis Reservoir in January, since there may not be much more forthcoming. Growers with limited supply should save as much as you can for Stage III (July through August) in order to promote as much kernel filling and splitting as possible. Start off the season with at least 75 percent (estimated) field capacity to four feet, and then try to hold out until May to irrigate, if water availability is limited or very expensive. Irrigating at 50 percent of Etc from bud break to shell hardening was not harmful to pistachios in our regulated deficit irrigation trials. It did result in smaller nutsand slightly higher early splits. However, deficit irrigating from early July to harvest has serious negative effects on kernel filling, crop weight, and split-nut percentages. Refer to last month’s task list for more information on allocation of limited water throughout the season.

Nitrogen: You have all heard of the UC Davis study (the Harter Report) about agriculture being the source of ground water contamination. Grandpa may be responsible, but he is not around to take the blame. We have to step up to the plate and be the BEST stewards of our nitrogen usage as possible. Hence, avoid nitrogen applications before fruit set. Remember that early shoot growth and fruit development is all from STORED NITROGEN! A good nitrogen management program includes soil, plant, and irrigation water N assessment. This means you should have samples taken of each so you can make a better assessment as to how much synthetic N needs to be applied to the soil to meet the plant/crop requirement. I suggest you begin this management process NOW, because it will most likely be EXPECTED of you in the near future!

Shortly after bloom, I would assess my crop load, check past soil analyses and then begin N fertilization at 30 to 50 pounds depending upon irrigation method and estimated crop load. Apply the higher rate under flood irrigation. Recent research by Dr. Patrick Brown, UC Davis, and Dr. Ismail Siddiqui indicates that pistachios remove 28 pounds actual N per 1,000 pounds of ACP weight from the orchard system. This value does NOT account for application inefficiency! Fertigation applications may be 80 percent efficient. Furrow/broadcast applications may be as low as 50 percent efficient. It is for this reason that pistachio growers have largely gone to drip irrigation for improved water and nutrient management. Back off on the N applied this season if you find soil nitrate nitrogen levels above 25 ppm per foot in the root zone. Nitrate nitrogen levels in the irrigation water must also be considered in your budget. A 10 ppm nitrate N level supplies 27 pounds of actual N per acre foot of water applied!

Adding high levels of N to the soil early in the season will NOT result in greater plant uptake unless the tree is deficient. Available data indicates pistachio growth and yield is not improved with July tissue levels above 2.5 percent. A validated model for predicting July nitrogen and potassium levels from tissue samples taken earlier in the season can be found at: http://www.plantsciences.ucdavis.edu/plantsciences_faculty/brown/Models/.... Created by Dr. M.I. Siddiqui during his doctorate studies with Dr. Patrick Brown, UCD Pomology Professor, this model allows growers to assess the future nitrogen status of their orchards from late April and May tissue samples. For example, a 3 percent nitrogen tissue analysis 40 days after full bloom would predict that you would have 2.68 percent in July, a level sufficient to begin kernel filling. I recommend you begin using this model, since laboratory testing last season showed it was an accurate prediction tool.

Micronutrient Sprays: Research shows good zinc uptake at 50 percent leaf expansion (late April). Use only 2 pounds of zinc sulfate 36 percent. Research by Patrick Brown and Qinglong Zhang indicates it is safe to add one-half pound of Copper EDTA or one pound of Solubor to the foliar zinc sulfate rate. Buffering this mixture to a pH of about 5 also improves zinc uptake by increasing the amount in solution. Acidification should be done with citric acid (powder) rather than phosphoric buffer to prevent zinc phosphate precipitation. Many growers prefer to avoid the “Betty Crocker” mix and apply liquid materials formulated for pistachios. Check with your supplier for suggestions, but be sure they have adequate amounts of copper, boron, and zinc.

This is especially true of two- and three-year-old trees. Deficiencies severely limit canopy development and reduce early bearing potential. They are also very common, suggesting growers are not taking young pistachio plant nutrition sufficiently seriously, and are suffering loss in orchard development because of it. My experiences suggest second-leaf orchards are especially susceptible to micronutrient deficiency, partly because of all the tipping performed to create branching. Three sprays are often needed to prevent loss of canopy development during this critical training year.

Shriveling flower clusters do not necessarily indicate fungal infection. Clusters that remain green and shatter off the tree could be associated with low boron levels. Boron-deficient leaves have crinkled edges but remain uniformly green and normal in size. Tissue levels less than 60 ppm in May suggests the need for boron fertilization. Boron is taken up by the leaves throughout the season, so application can be made at any time during the spring. Correcting severe deficiencies may require 2 ounces of Solubor PER TREE (16 lb/ac) soil applied! Yes, you read it right. It’s not a typo! Pistachios are boron pigs!

Pest Management: Beating tray monitoring and sweep-net sampling of true bugs should be initiated. The native vegetation surrounding pistachios is still somewhat green for now, so the migratory plant bugs have no reason to move…yet! That will quickly change as we move into April and early May! Navel orangeworm (NOW) traps should be in place. The Suterra NOW adult lure, looks to be very effective in catching adults from trapping data collected last season. Running both egg and adult traps will certainly assist crop consultants to interpret the wing-trap data. Research suggests pistachios compensate for nuts lost to Phytocoris and Lygus feeding, so early chemical treatment, specifically for these pests, may not be needed unless you have significant BOT and Calacoris is your predominant plant bug present prior to shell hardening. Most growers routinely add a pyrethroid to their mid-April nutrition spray to cover this issue. Donnie Thomas, private pest consultant, also likes to assess the presence of Gill’s pistachio mealybug at green tip using his beating tray. He beats ten trees per area with his tray beneath the shoot tips, and then surveys the tray for grey, immature mealybug stages that have crawled up the trunk during the warm February weather. Donnie says this has really helped him determine if he is going to have a problem in June. I would appreciate feedback from others who experiment with this.

Weeds: Weed control is critical this time of year, especially London rocket and spotted spurge which are preferred hosts for false chinch bug. When these weeds dry, the chinch bugs can roar out onto your young budded trees and kill them with the toxin associated with their mass feeding. Clovers, Russian thistle and birdsfoot trefoil are just a few of the weeds serving as hosts for lygus (grasses are not hosts for lygus) and stinkbugs. If you did not get the importance of removing London rocket and spotted spurge, read this paragraph over again, or suffer the consequences of dead trees from false chinch bug!

Happy farming!