Based on the wide range of pistachio nut fill he observed at mid-July, some growers may be money ahead this year by performing two harvests, suggests Bob Beede, University of California Cooperative Extension farm advisor for Kings County.
Because of the cool spring weather, nut fill in the Central San Joaquin Valley didn’t begin until the first week of July — about two weeks later than usual. As a result, he doubts that most growers will start shaking trees until mid-September. In the meantime, checking the nut fill could be a big help in deciding when to start harvesting this year’s crop, he says.
Beede was surprised by what he found the second week of July, when he evaluated kernel filling in some West Side orchards. “The range in percentage of nut fill was quite great. The majority of those I cut were between 30 percent and 40 percent kernel filled. But, a significant percentage of the kernels were BB size or smaller. Those nuts will mature later, and most likely will be non-split nuts.”
A wide variation in kernel fill, he says, indicates just how variable nut maturity is likely to be this year. “If I were a grower, I’d be out right now, cutting as many as 200 to 300 nuts, randomly selected from the canopy, and then sorting them by kernel size to get some idea of what proportion of the crop is behind in maturity,” he says.
“That will give you a very good idea of what percentage of nuts you’re likely to remove in the first shake.
“If you find a wide variation and can control your harvest date, you will benefit from a “bump and run” approach on the first shake,” Beede says.
“Bump and run means going in relatively early and harvesting the most mature nuts. Then, you wait two weeks for the rest of the nuts to finish filling and maturing before shaking the trees a second time. It’s not for every grower, and those considering it must weigh the added harvest cost over the estimated benefit in crop value.
“It’s my guess that the two-harvest approach has a greater effect on the weight of the non-split nuts, rather than significantly increasing split nut numbers. It also helps reduce dark stain on early maturing split nuts, which are subsequently graded as shelling stock because of staining.”
A continuation of the favorable July temperatures — not exceedingly hot — might help minimize the adverse effects of the cold spring weather on the split percentages this year, he says. Less-than-optimum temperatures in the spring reduced the amount of food the leaves produce through photosynthesis, which reduces the amount of reserve food for kernel filling from July to harvest.
“Hypothetically, the tree begins Stage III (kernel fill) with fewer carbohydrates stored in current season growth from the cold spring,” Beede says. “Research by Tim Spann, now a University of Florida horticulturist, indicates pistachio leaves begin to decrease photosynthesis when temperatures exceed 86degrees.
“So, milder summer days provide slightly longer periods for maximum photosynthesis, which may possibly make up for some of the losses encountered during this spring.”
As of the third week in July, the pistachio orchards in his area were in fine condition.
“They look good and extremely clean,” he says. “Growers have been diligent in meeting the nutritional requirements of their trees. They’ve done an excellent job of minimizing the botrytis threat from the excessive spring rains and have spent considerable sums of money on extra sprays to insure the highest quality crop up to this point. They have finished their second generation navel orangeworm treatments.”
It remains to be seen how successful their fungicide treatments will be in combating the two main summer disease threats — alternaria and botryosphaeria.
In the next few weeks, field work will be aimed at maximizing nut fill by preventing water stress — keeping weeds under control so they don’t compete for water, irrigating, and insuring adequate nitrogen and potassium are available for the final stage of nut development.