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California Pistachios: Tips On Harvest-Time Irrigation, Pest Management

Owen Taylor
By Robert Beede, U.C. Farm Advisor, Emeritus, Kings County, California September 3, 2017

California Pistachios: Tips On Harvest-Time Irrigation, Pest Management

Growers started shaking Golden Hills and Kalehgucci the week of August 22 in 2016, but I just had lunch with Carl Fanucchi (grower and consultant), who said they were not going to get going this year until the week of August 28. I know that every orchard is different, and yours might be earlier. Bu generally speaking, it would appear that harvest this year is 7 to 10 days later than last year.

I just talked to Chris Wylie, ranch manager for Agri-World in Madera, and he agreed, stating that if he did not have so much ground to cover, that he would not begin light shaking until the first of September.

It is also generally agreed that there are quite a few pistachios out there. I am not going to venture a guess, because that is a marketing issue best left up to marketers. However, I see good crops on both young and old orchards, with considerable variability between trees within a given orchard.

In spite of the insect pressure this year, I see good quality in orchards with sound pest management programs. I also have not yet seen one orchard with substantial Botryospheria or Alternaria, thanks to the efforts of the crop consultants and efficacious fungicides available for control of these two important diseases.

In order to maintain an even flow of product into the processing plants, several large ranches have plans to run day and night. Safety becomes a big concern when people have to press this hard, so keep reminding everyone to watch out for one another to prevent an accident. It happens in an instant, but the memory lasts forever. Do not assume that the other fellow sees or hears you over the equipment noise.

Many of the orchards I walk have substantial numbers of early splits. Be on the lookout for navel orangeworm damage within them to keep the quality up and collect the premiums. At some point, aerial sprays probably are better than ground because they optimize timing. Ground treatments would have to be completed in three days or less in order to make them worth the additional effort at this time, in my opinion.

It has been hot, and it remains hot, so be careful not to cut the water back too much until we get some cooler weather. Crop water use has probably been five percent greater this year due to the sustained heat.

Pest Management:

Navel orangeworm is still the pest to beat, and the almond growers report high pressure after hull split. Trap and visual monitoring is critical at this time, and if your crop consultant tells you to treat, do not argue with him or her.

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 20 in the Madera area, using Dr. Joel Siegel’s method of DD accumulation from January 1 and the Parlier CIMIS station.

Dr. Siegel, USDA-ARS, says there may be time for a possible fifth generation of NOW in the fall, depending on future temperatures.

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 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 Points

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% 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 almond, 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% 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. Augering 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, provided 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.

Owen Taylor
By Robert Beede, U.C. Farm Advisor, Emeritus, Kings County, California September 3, 2017