California Pistachios: How – And When – Will Harvest Shape Up?

I think nut maturity is about a week ahead of last year, due to the warmer spring. Growers in Kern County are going to try light shaking Kerman (only about 2 seconds) around August 25. Craig Kallsen, UCCE Farm Advisor, Kern County, and field director of the pistachio breeding program, says Golden Hills (GH) usually matures more uniformly than Kerman. He plans to harvest GH in Buttonwillow on August 26, which tends to be a late maturing area.

He thinks earlier areas might be ready by August 23. It would be great if those of you with Golden and Lost Hills E-mail Craig during harvest with your observations on removal and harvest timing. 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. Thanks for the good tips, Craig!

In years with erratic leaf out 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”, 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 (40F minimum threshold, no maximum) were the lowest in ten years, 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 1,970 D0. Many south valley growers started the 2012 harvest around September 10.

The spring degree-days for 2013 were 200 D0 more than the average, so it would explain why crop maturity was about a week early last year. This year we have 250 degree-days more than average, so there is reason to believe harvest might start a couple of days sooner 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 are much higher than last year in many orchards. One grower reported 80% blank nuts in a growing area with warm winter temperatures and severely delayed leaf out. The orchards I have cut show total blank nuts from 15-33%. 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 vary in number from orchard to orchard. With the young trees on line this year, I do not see why we do not have the potential for a 500 million pound crop. That’s my guess.


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