September/October Pistachio Task List

By Bob Beede, U.C. Farm Advisor, Emeritus

Harvest: I think nut maturity is about the same as last year. Chris Wiley, Agri-World Ranch manager, and veteran of over 35 harvests, called the other day lamenting the loss of a “normal” harvest year. Like a fine wine, he reminisced about the “harvest of ‘98,” when a single five-second shake rained all the nuts onto the catch frames with great quality.

The observations of Chris and many others suggest that this harvest is NOT going to be a vintage year. Individual trees vary greatly in maturity within a given orchard, and the percent-fill will not be known until the first grade sheets are available. If you have been out cutting clusters, you at least have some idea what to expect. Those who have not are going to be asking to recheck the bills of laden, thinking that several loads never made it to the processor.

Based on what I have observed, Golden Hills has better set and fill than Kerman, which suggests that this cultivar is not only 14 days earlier than Kerman, but that it also has a lower chilling requirement. In other commodities, earlier maturity correlates pretty closely with lower chilling. I wrote about the effect of insufficient chilling on fruit set and development in the last task list, so reference it if you need more information on this subject.

Craig Kallsen, UCCE farm advisor, Kern County, and field director of the pistachio breeding program, says Golden Hills usually matures more uniformly than Kerman. Craig also reminded me to tell you that Golden Hills splits before the hull tatters, so watch carefully for the creamy, swollen hull development in timing harvest.

In years with erratic leafout and bloom, two shakes are common for Kerman in order to harvest the early set nuts before the navel orangeworm infests them. A second shake, where crop load justifies it, is performed about 10-14 days later. Examination of temperature patterns from previous years suggests pistachio maturity is affected more by spring temperatures than summer. Cool springs delay harvest, presumably because the heat units needed for maximum plant efficiency early in the season are not reached.

Peach research shows that there are optimal “degree growing days,” (DD) in which the carbon accumulated by photosynthesis is directed largely into crop development, and not “lost” in the form of CO2 from respiration. Excessive carbon lost in respiration during hot springs is the equivalent of lost interest in a compounded interest savings account. Once interest is lost, your total is always less than what it could have been.

In 2010, the degree-days (40° F minimum threshold, no maximum) were the lowest in ten years (1703 DD), and many growers did “bump and run” shakes to get some crop to the processor, since the bulk of it was 14 days behind. The degree-day accumulation between April 1 and June 15 for 2012 was very close to the 30-year average, which is 1970 DD. Many south valley growers started the 2012 harvest around September 10. The spring degree-days for 2014 were 2217 DD, 247DD more than the average, so it would explain why crop maturity was about 7-10 days early last year.

This year we have only 100 degree days more than average, so there is reason to believe harvest might start a couple of days later than last year. Crop load is all over the board, depending upon previous yields, tree age, and how adversely your orchard was affected by insufficient chilling. Reports from the field indicate blank nut percentages vary as much as last year. The orchards I have cut show total blank nuts from 20-60 percent. Realize that about half that percentage gets left in the tree, since I cut entire clusters rather than randomly selected nuts for accurate blank nut assessment.

All the crops I have seen look clean, with variable nut size depending on crop load. The crop consultants have succeeded in keeping the navel orangeworm away from the early splits, which were very low to almost zero in the orchards I walked. I do not see the potential for more than 450 million pounds this year. That’s my guess, and it is worth exactly what you paid for it!

Pest Management: Navel orangeworm is still the pest to beat. Although many growers have sufficiently low NOW pressure to require only two sprays, others with high populations apply five or more sprays for both plant bug and NOW. The 2700 DD timing occurred about August 4, using Dr. Joel Siegel’s method of DD accumulation from January 1 and the Parlier CIMIS station. Dr. Siegel, USDA-ARS, says there is enough additional degree days for possibly a fifth generation of NOW in the fall, so be sure to survey what is left in the trees after harvest, and get it on the ground if you can early to reduce your overwintering population.

Weekly monitoring of split and mature nuts during harvest is a must. The research data shows pistachio worm damage can increase by one-third to one percent per week, depending upon the season. Aerial applications have looked good in Joel’s research as cover sprays during harvest. Be sure to use a material that kills adults. Remember that prompt harvest is one of the BEST control methods for NOW! Dr. Siegel’s NOW infestation rate curve for Kings County suggests growers have about 21 days from the very beginning of harvest before NOW damage rises like a Saturn rocket. Review of the payment penalty now assessed by most processors for offgrade, including insect, shows how costly wormy nuts become. The buyers are also looking for a way to beat back the pricing structure on pistachios, so do all you can to deliver a clean crop!

Cultural: I am anxious to see what this year’s split percentages are. Depending on water availability and time of application, we could see a wide range in split percentages. Research by Vito Polito, U.C. Davis Plant Sciences Department, indicates shell splitting is caused by the physical expansion of the kernel rather than development of an abscission zone. Split nut percentages are affected by all of the following: low boron and zinc, insufficient water from July 1 to harvest, excessive cool weather during the growing season, time of bloom, and heavy big bug damage during kernel filling when nuts show no symptoms.

Waiting for increased split percentages at harvest after much of the crop has creamy hulls can backfire from higher stain (especially on the east side of the Valley where Alternaria is a bigger problem) and insect percentages. So, do NOT wait! Growers with poor split percentages need to examine their irrigation program during stages 1 (shell development) and 3 (kernel filling).

Research by Dr. David Goldhamer shows that split percentages can be improved by inducing regulated plant stress during Stage 1. If you typically have good split percentages, the gain from Stage 1 stress is primarily water savings. Growers can save 50 percent of ETc between April 1 and June 1, and in northern California, irrigation may not be necessary at all during this period. Split percentages can also be affected by the uniformity of water application. There is no question water stress during Stage 3 reduces split percentages. Compare your applied water to the following average water use: July is 9.8 inches, August is 8.3 and the first two weeks in September is 2.8 inches. Deciding when to stop irrigating before harvest is dependent upon weather, disease pressure, soil texture, split development and orchard access.

If Alternaria pressure is not a factor, water right up to within three or four days of shaking. Unlike an almond, a pistachio does NOT require an extended “dry down” period to avoid trunk damage by the shaker. In pistachio, it is common to still be irrigating blocks awaiting harvest while shaking. A little post-harvest water (25-50 percent of ETc) is advisable for relieving shaker stress and improving nutrient uptake in the fall. I have visited several orchards with sparse canopy development. This is very characteristic of insufficient water during leafout in our irrigation research. Nut size is also affected. Auguring these orchards showed moisture to only 18-24 inches!

In addition to inadequate nutrition (zinc and boron), it is my professional opinion that the time of bloom and pollination affect split percentages at harvest. In high chill years, pistachio trees have the potential of pushing and blooming early, PROVIDING the weather is favorable. When spring temperatures are warm, bloom occurs early and sharply. This, in my opinion, allows for more uniform nut development and size since they all begin at about the same time. But when spring temperatures are cool and erratic, I believe nut size and expansion reflects this. Consequently, some nuts pollinate late and experience different developmental weather than those setting earlier. These subtle differences may affect the AMOUNT of cell division and the RATE of cell expansion during shell development. The result is that some nuts have thinner or smaller shells, which are more prone to premature splitting. We really need to research this so I can quit giving you my coffee shop opinion!

Diseases and Insects: I would be amazed to hear of problems with Botryosphaeria in the south valley this year, considering we do not have enough water to flush a toilet. But it does not hurt to be on the lookout for it during harvest so that a strike-cutting program can be initiated in the fall, if necessary. We have had few infection events for BOT in the southern valley this year, but northern California has constant pressure.

Alternaria has not shown up yet (August 16) in orchards with two sprays, so the new materials appear very effective. As leaf tissue ages, its susceptibility to Alternaria infection increases due to decreasing sugar content. Warm temperatures and high humidity increase the Alternaria potential. Look for yellowing leaves, which have black necrotic lesions and spores in the center. This differs from the common yellowing that occurs on fruiting spurs, which is the result of nutrient extraction by the developing kernels. Also examine the leaf stem (petiole) and main vein. Rub the area with your fingers to see if some of the black comes off. If so, this is Alternaria. Assess how much exists in the canopy and look for small black lesions on the hull tissue. Remember that Alternaria DOES NOT kill nut clusters and shoots. Botryosphaeria does that. BOT also does not rub off on your fingers when you handle the infected tissue.

Leaves uniformly brown low in the canopy can be easily mistaken as Alternaria infections when, in fact, they are simply dying from lack of light or water stress. How do you tell? Look for the black spores that rub off on your fingers! If there are no spores and the leaves are UNIFORMLY brown rather than having angular sections of brown with black spores in the center, they are shoots that have simply shaded out. They could also be infested with Pacific mite, which is rare in pistachio. Check it out with your hand lens!

Alternaria can cause economic damage from defoliation and nut staining. Following harvest, you should determine if pruning, irrigation and soil management practices might be modified to reduce the problem. Poor pruning and slow water infiltration are common causes. Consider applying gypsum in June rather than in the winter to improve the surface soil structure. My desire to minimize Alternaria infection through good cultural practices is based on the limited materials we presently have registered for this disease and the rapid resistance that develops from their frequent use.

Do not confuse citrus flat mite, Pacific mite, or rain damage for Alternaria. Several calls typically occur at harvest concerning dried clusters on the tree that cannot be removed by the shaker. Citrus flat mite causes patches of chocolate brown discoloration on the hull and rachis tissue rather than the distinct, round lesions about 1 mm in diameter associated with Alternaria. Flat mite discoloration is also only on the surface, so scratch the tissue to see if it is green underneath. Citrus flat mite also does not attack leaf tissue and cause black necrotic margins. This tiny, orange-colored mite can turn entire clusters brown and render them unharvestable. Citrus flat mite damage can be confused with BOT, but flat mite does NOT cause gumming or blackening of the cluster like BOT. Wettable sulfur in June or July is the cure for flat mite.

Also, if you are near a dairy, do not confuse fly speck for flat mite! Pacific mite defoliates trees in patches of the orchard. Browning begins inside the tree canopy, and works it way out, causing leaf loss with mite levels as low as one or two per leaflet. Pacific mite and Gills mealybug problems are on the rise with multiple pyrethroid sprays against NOW. Reports from the field indicate Gills mealybug has really spread this year. Super clean nuts are coming with added cost! Softer NOW management programs are the key to future cost control.

Do not confuse leaf scorch, common on the male "Peters" variety, for Alternaria or Botryosphaeria. Male scorch is thought to be caused by heat, and it may predispose the males to Alternaria, but this disease did not cause the initial leaf browning.

Young Trees: Budding young trees could also still be done, but by the time you read this (late August) I think it is too late to push them by cutting back the rootstock and notching above the bud. Forcing fall buds greatly increases the risk of frost damage by depleting stored food spent on new growth. This potentially deadly practice is becoming more common with Golden and Lost Hills buds, because they require a slightly bigger rootstock diameter to accept the larger bud shield than Kerman. Hence, trees are being budded later, and the temptation is to “beat the odds” and push them late into the fall.

Instead, after the buds take, begin slowing vegetative growth by cutting back on the water. How you decide to handle your newly budded trees is your call, but young orchards suffering from fall cold damage has increased markedly in recent years because the trees are being pushed too late. Most growers observe an early to mid-September irrigation cut-off on first- and second-year trees to harden them off. Timing the irrigation cut-off requires knowledge of soil water content, plant vigor, and estimated remaining growing time. It is better to stop them too early than force them too late. September and October is not the time to try and make up for growth lost during the season. It is much safer and smarter to get them to bed alive and then start off with good vigor next spring.

Dr. “Z,” our new crop physiology professor at UCD now has data to SHOW that cutting off the water to young pistachios DOES precondition the trees, and make them more cold tolerant. Carl Fanucchi has been telling you this for years, but only wise men listen! I strongly recommend growers force young trees into dormancy with zinc sulfate 36 percent at 40 pounds per 100 gallons of water or 10-15 gallons of liquid zinc 12 percent in 85 to 90 gallons of water. Liquid 12 percent is manufactured from zinc sulfate dissolved in sulfuric acid. Consequently, it has an acidic pH, which I think does a better job than 36 percent powder. But alas, no data, just opinion!

Check with your crop consultant or other experienced growers for their thoughts. Also, I have seen more boron deficiency this year than in the past, so be sure to review your August tissue levels so that you could add some boron to your fall herbicide spray, if needed.

That’s all, folks. I wish you a Happy, Safe, and Prosperous Harvest!