California Pistachios: Crop Assessments, Observations From Bob Beede

Even though we received good winter chilling this year, the cool spring weather has delayed pistachio leaf out and bloom by 5 to 7 days. This spring is a great example of how, even with good chilling, pistachio plant development can be delayed by cool temperatures.

The overlap between Golden Hills and Randy looked very good. Randy is a very prolific male, even when young, and provides lots of pollen for young trees just coming into bearing.

The overlap between Kerman and Peters was not quite as good. I rated Peters at only 10-15% bloom when Kerman was at 40% bloom. However, the flower clusters are developing nicely, and I have not seen any sign of poor pollination in mature orchards.

The Peters males in young Kerman orchards have always lacked adequate pollen to maximize set in the more precocious females.

Why Artificial Pollination Falls Short

The research attempts at documenting yield improvement using artificial pollination have also resulted in no measurable improvement. In addition to the complexities of harvesting, storing and distributing the pollen, one has to remember that one or two artificial pollinations are single events, not processes.

By this, I mean that natural pollination occurs 10 to 12 hours per day over a 7- to 10-day period. The presence of freshly emerged natural pollen has greater probability of landing on a newly receptive female flower stigma for rapid germination.

Female flowers vary in their date of receptivity within the inflorescence, as well as throughout the tree. So, having adequate natural pollen present constantly is much different than attempting to augment the pollen load once or twice during the span of female flower receptivity.

The occurrence of these artificial “events” does not appear to be sufficient to significantly increase fruit set. Placing branches of natural pollen in water buckets hung at the young male tree locations has shown some improvement, but pistachio shoots plug up their vascular system with resin quickly, and thus greatly reduce the life of the expanding male inflorescences.

Preserving the cut male shoots by preventing resin plugging could help greatly in extending their life and pollination effectiveness.

Off Year? That Depends

During pruning, people talked about this being an off-year, but my visitations to many orchards, young and old, suggest there could be 750 million to 800 million pounds out there! I have seen several orchards with crop loads I estimated at 5,000 pounds, if most of the clusters set.

At the time of this writing, we are now moving into the BB stage of nut development, and the canopies have leafed out sufficiently for the very important nutrient spray.

As I have written many times, leafing date and spring temperatures have a greater effect on harvest date than summer temperatures. This is because spring temperatures have a greater effect on the rate of carbon fixation.

In the summer, the rate of carbon fixation is maxed out rapidly in the morning, and limited by temperatures exceeding that for optimal photosynthesis in the afternoon.

During really hot days, considerable carbon could be expended in respiration. All of this physiology desperately needs to be researched, and I am shocked that there are no UC researchers interested in doing so. I also have observed many orchards being irrigated too heavily too early.

The cool spring weather delayed leaf out has reduced the water use schedule for pistachios by about 10 days.

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