Pistachio Orchard Task List for July 2018
By, Bob Beede, U.C. Farm Advisor, Emeritus
Crop Update: Hey, did you hear about the two pistachio farmers who pulled their pickups next to one another to ask what the price of WORMS was this year? The answer is up to 20 cents more per pound from base price for super quality. We have to have clean nuts to run the marketing program, folks. One processor had 400 of their 700 employees on the belts looking for infested nuts last year! Until we can come up with a more sophisticated identification process, this is what processors have to do to keep consumers buying an expensive product. As you know, there is damage other than insects that contribute to the overall reject percentage that affects your premium. I suggested in a past article that it might be possible to eliminate a good portion of these nuts by running them over a portable pre-sorting machine in the field, prior to dumping them in the trailer. The product arrival time is slow enough to possibly run it over an electric eye, air-leg sorter. This idea has been met with raised eyebrows of doubt to some, but it certainly would be one method of delivering cleaner product!
This year’s cool spring suggests harvest is going to be later this year than last since early season photosynthesis and carbon fixation is not optimized under cool temperatures. Comparison of the degree day accumulation for 2018 between March 10 and June 20 to the 30-year average suggests that 2018 is only 84D0 ahead of the average. Last year was 180D0 ahead of the average, and 2014, a very early maturing year, was 300D0 ahead. The best way to assess the effect of spring weather on crop development is by monitoring the completion of shell hardening, and the beginning of kernel fill. It would stand to reason that late blooming flowers would be slower to complete both of these important crop development indices than flowers that bloomed early. Noting the date of shell hardening and kernel fill annually provides a reference for comparing previous years, whose harvest date is known. It also tells you when your nitrogen, potassium and water need to be optimized to avoid reductions in kernel growth rate and increased non-split nuts.
To assess kernel filling, randomly collect 10 ENTIRE clusters from a selected area of the orchard in a five-gallon bucket, making sure that they represent fruit borne from each of the four tree quadrants (north, south, east, and west). Find a comfortable, shady area to work, because you are going to be there for 45 minutes. Strip the nuts off the rachises, and then place the nuts in a container you can easily access. With a pair of hand shears, cut EVERY nut in half. Those preferring to cut them horizontally should hold the base of the nut while they remove the upper, tapered tip. I prefer to cut the nuts lengthwise because it makes viewing the developing green embryo at the tip of the faniculus easier. However, cutting lengthwise must be done with greater care to avoid catching the flesh of your index finger in the shears (a bloody mess!). Rate the cut nuts for percent of complete kernel fill, and then place them under one of five categories labeled 0 to 5 (0=no fill, 5=completely filled) written on a piece of cardboard, or large coffee cups. When you are finished cutting all the nuts, count the number in each category, and do the basic math to determine the percentages of each. WRITE DOWN the results! Performing this task at least every two weeks will tell you a great deal about what to expect at harvest relative to maturity and crop load. It will also tell you if the large bugs are having lunch at your expense by the presence of misshaped kernels or tiny dark spots in the kernel or on the funiculus. If the kernel appears to be drying up, look around the base of the nut, which is much softer and easier for the insects to probe.
Soil and Water Management: Kernel filling requires lots of water, nitrogen, potassium, and boron. Average water use in July is 9.8 inches (55 gal/tree/day, 150 trees/ac). August water use is 8.2 inches (50 gal/tree/day). Keep an eye on the temperatures and adjust your schedule accordingly. If you do not have any soil moisture monitoring equipment in the orchard, be sure to auger weekly to check for moisture below two feet. The surface can look mossy and wet, but the lower depths can be dry as chalk. Believe me, deficit irrigation sneaks up on you, and before you know it, your trees are stressed and limited in kernel filling rate! The amount of water applied must be greater than the tree’s water requirement because of application inefficiency (70-80% efficient in basin or furrow systems, 85-90% in low volume). Deficit irrigation, zinc or boron deficiency, and cool weather during kernel filling will dramatically reduce split nut percentages.
Spread gypsum at one to two ton per acre if infiltration is becoming a problem. Standing water increases your foliar disease risk due to greater humidity. Irrigate every other middle rather than stretching irrigations out to reduce standing water and tree stress. This is especially critical if you are on shallow soil with limited root mass. Remember: no water = no splits = no money! In the WORST cases, rip down the middle of the row with a single 24″ shank to get water into the root zone. The stress caused from in-season root pruning is small compared to dry trees. Irrigate IMMEDIATELY after you rip! A professional soils and water adviser can assist you in assessing the need for such drastic action.
Pest and Disease Management: Dr. Siegel’s research suggests that 1700, 2200, and 2700 Degree Days from January 1 are key times for evaluation of your NOW population since they mark rises in NOW activity. EVALUATION does NOT mean BLANKET SPRAYING! Dr. Siegel’s research confirms that NOW cycles MUCH faster on new pistachios, so much so that they can complete a generation in 500-600 DD0! Dr. Martin Barnes (Dr. NOW of the 1970’s at UC Riverside) also reported this back in the 1970’s. Hence, Dr. Siegel suggests orchards under HIGH NOW pressure may require re-treatment at 2200 and 2700 DD0 from January 1. The need to do this in YOUR orchard is a decision between you and your crop consultant, SO you need to get together with your crop consultant NOW to discuss what they are seeing and what THEY recommend you do. According to the excellent Degree Day monitoring service Dow AgroSciences provides (Email: dowagrosciences@pestclues.com to get added to the weekly mailing list), the overwintering NOW generation just ended about June 18. This is six days later than last year. The beginning of the second generation is going to fall right on top of the early suture development in almond, which could increase that crop’s insect pressure. It could also spill over into pistachios later when the almonds are harvested, so try to stay abreast of what your almond neighbor is doing to protect his crop.
The impact of the second flight greatly increases in pistachios with the occurrence of early pea split nuts. Pea split nuts allow the overwintering generation of NOW to transition onto the “new crop”, and thus develop at a faster rate, due to the improved food source. Pea splits typically do not occur before the first week in July. Don Thomas, a crop scout for 30 years, tells me that 25 pea splits found in three minutes spells big trouble, so get out in the orchard and monitor for these! Don’t ask your crop advisor to do it all! There is no way they can spend the time scouting your field the way you can. Help them out, so you can help yourself get that 20 cent premium!
Dr. Joel Siegel has developed an outstanding table to ASSIST growers in their NOW management decisions. This table does NOT constitute a recommendation! Use this very valuable tool in your discussions with your crop advisor to customize your pest management program. In order to provide this table for this article, Joel agreed to share this DRAFT with us. Changes to this table will be posted on my Kings County Webpage. Joel has also reminded me of published research by University of Illinois colleagues of his, in cooperation with an entomologist, Brad Higbee (formerly with Wonderful, and now with Trece), which showed pyrethroid resistance development. At the time of the study, NOW’s tolerance to
pyrethroid was reportedly as high as 16 times the control group. I am told that field failure can begin when tolerance reaches 20-fold. Dr. Siegel’s colleagues at Illinois University also showed resistance remained stable for at least 10 NOW generations under laboratory conditions. Although pyrethroids are still effective in the field today, our heavy reliance upon them may come to an end due to resistance. Dr. Siegel states that there is also no new chemistry within the pyrethroid class to explore. This information makes timing and execution of treatments all the more important. Between the difficulty in thoroughly winter sanitizing pistachios, and the thousands of acres of nut crops now present in the southern San Joaquin Valley with varying degrees of NOW management, it is no surprise that attempts to apply IPM principles prove very difficult. It is for this reason that I hope to see mass Mating Disruption in pistachio and almond before I take my last breath!
Table 1. Suggested pistachio spray strategies for navel orangeworm. Dr. Joel Siegel, USDA/ARS
Maximum Label Rate Strategy-your choice:
- For Altacor (IRAC 28) it is 4.5 oz/acre
- For Besiege (IRAC 3A+IRAC 28) it is 12.5 oz/acre (this corresponds to 3.79 oz/acre of Altacor and the maximum rate of Lambda-cyhalothrin; if you choose to maximize the Altacor component you can add Altacor at 0.71 oz/acre) For Intrepid (IRAC 18) it is 24 oz/acre
- For Intrepid Edge (IRAC 5+18) it is 18 oz/acre
- For Lamda Cyhalothrin (IRAC 3A) {LambdaCy, Warrior II etc.} use 2.56 oz or 5.12 oz/acre depending on the formulation. CHECK LABEL.
- For Minecto Pro (IRAC 6+28) it is 12 oz/acre
Continue to watch for leaf-footed plant bug and stink bugs, which are difficult to detect after shell hardening. This is because the hull and shell do not develop the brown lesion characteristic of bug damage when the shells are soft. Nuts observed now with external lesion symptoms are old damage. New feeding will often show a tiny, clear bead of sap on the hull from where the stylet penetrated. Do not forget to look for new damage at the base of the nut where it attaches to the stem. This is the “Achilles’ heel” of pistachio since it remains softer and the insects somehow know this! Feeding at this site can cause loss of the developing kernel. Big bug feeding elsewhere on developing kernels causes distortion, sunken areas and black lesions in the meat (kernel necrosis). Carry a pair of hand shears during orchard monitoring. Select nuts randomly and cut them open to examine evidence of recent kernel damage. Stigmatomycosis, a fungal yeast infection resulting in wet, slimy kernels is also transmitted by the big bug mouthparts penetrating the kernel. Keep your UC/Pistachio industry insect guide handy for reference in the field.
Watch out for the citrus flat mite, a common pest in July that turns the rachis and hull tissue brown from feeding. Pacific mite infestations also occasionally occur in pistachios. Unlike citrus flat mite, the pacific mite can cause damage at low populations (3-5 per leaflet). Defoliation during kernel filling can greatly reduce crop quality. Research suggests pacific mites do not thrive on pistachio. Six-spotted thrips are very effective predators. My research on various miticides in 2000 indicated oils of all types were as effective as synthetic compounds. Observations also indicate the addition of spreader-stickers to oils is not advised due to possible russeting of the hull tissue which could increase the potential for Alternaria infection later. Slight phytotoxicity may occur with oil applications made close to wettable sulfur.
Orchards with past Botryosphaeria (BOT) infections benefit from two sprays; one in mid-June, and another close to mid-July. The strobilurins remain very effective against BOT, because the sexual stage of this disease is not present in pistachios, and its genetics remain very stable. This is NOT the case for Alternaria, whose genetic makeup is constantly changing, and thus it develops resistance to new fungicides within a couple of years, depending on the frequency of application. Treatment timing for Alternaria is the same as that for BOT. Orchards with a history of Alternaria should be on their second spray by mid-July. Waiting until symptoms to appear in August is too late for disease control. High humidity and dense canopies both favor buildup of Alternaria inoculum. Look for patches of brown necrotic tissue on the leaves with black sooty material that rubs off on your fingers.
Fertilization: U.C. Davis research shows kernel filling is a period of high nitrogen demand. On-year trees took up 35 percent more nitrogen during kernel filling than off-year trees. The nuts accounted for more than 90 percent of the accumulated nitrogen for the entire season. The total nitrogen requirement for on- year trees was calculated at about 150 pounds. Research by Dr. Siddiqui and Dr. Patrick Brown indicate 28 pounds of N is required per 1000 pounds of ACP weight pistachios. Add 25 pounds of N during the on- year for tree maintenance. These guidelines do not include inefficiencies in the application, which can run as high as 50% when applied by the water-run method. Off-year trees accumulate most of their nitrogen in the canopy branches. Yellowing of leaves adjacent to nut clusters is common in heavy bearing trees. This occurs even when tissue levels are considered adequate (2.5%). Some growers report less yellowing with higher nitrogen applications. This has not yet been researched.
Potassium (K) uptake is also very high during kernel filling. Research by Drs. David Zeng and Patrick Brown indicate potassium applications up to 200 pounds actual K per acre applied in equal amounts over the months of May through August significantly increased yield, split nut percentages, nut weight and reduced blank and stained nuts. Reductions in staining were associated with less Alternaria leaf infections at harvest. Siddiqui and Brown indicate 25 pounds of K are required per 1000 ACP pounds of pistachios. The greatest response to K fertilization was on soil whose potassium availability was limited by either low soil K or high fixation within the soil. Young alluvial soils such as those on the west side of the San Joaquin Valley are very high in exchangeable K, and thus less likely to respond to potassium fertilization unless confounded by salinity or extremely light texture. Zeng and Brown suggest the August tissue level for K should be about 1.7% for optimum plant performance. No elevation in chloride was observed in the leaf tissue from chloride-containing potassium sources after three continuous years of application. However, consideration of orchard health, soil permeability and stratification should be given prior to performing large-scale KCL applications.
Happy farming!
