Normally, harvesting of the California pistachio crop begins around Labor Day or shortly thereafter in the southern end of the San Joaquin Valley.
Not this year. The cool spring weather delayed the start by about 10 to 14 days.
“Supplies of 2009 crop pistachios are beginning to run low, and processors are looking forward to getting new product,” says Bob Beede, University of California Cooperative Extension farm advisor for Kings and Tulare counties. “Growers were ready to rock — but the music wasn’t playing yet.”
They’re dancing now, though, as harvesting moves into gear for light shaking of early-maturing nuts in some Kern County orchards.
Judging by what he’s seen, Beede expects nut size to be good and quality high. This follows what has been the coolest growing season in some time. In fact, he says, data show that heat units for 2010 are the lowest in 10 years.
Low heat units not only delays maturity of the crop, but could also affect growth of the kernel inside the shell. That, in turn, could reduce the percentage of splits this year, especially in northern California orchards with traditionally fewer degree days.
“Unlike nuts that develop a physiological abscission zone for splitting, pistachios split open physically when the kernel outgrows its house,” Beede says. “The cool spring allowed the shells to reach maximum size without limitation from water or heat stress, but the initiation of kernel growth was about 10 days behind average. Late kernel development could result in insufficient time for them to grow larger than the shell size.”
Beede is also concerned as to whether growers who opt for a two-shake harvest are able to return for the second shake when the remaining crop maturity is still optimal, and not overripe. An excessive amount of late harvest could jeopardize the overall quality of the California crop.
In a year like this, when the maturity of nuts in a given orchard can vary widely, double shaking allows growers to maximize crop quality — but the practice depends upon the maturity spread, crop load, and a grower’s control over harvest timing.
The idea is to shake the earliest-maturing fruit, which often is the best quality, at the optimum time, and then come back promptly 10 days later and shake the trees again to gather later-maturing nuts when they, too, are at peak quality.
This practice can eliminate the threat of staining when early-maturing nuts are left on the tree too long. It also enables processors to begin drying, roasting and marketing the nuts sooner.
Still, Beede doesn’t always recommend the “bump-and-run”, two-shake harvest program.
“Deciding on two shakes requires careful consideration,” he says. “The decision has to be made on an orchard-by-orchard basis. If you’re going to do a bump-and-run, you have to be able to control when you do the second shake.”
In addition to the added expense of a second shake, this approach risks harvesting the pistachios after nut quality has started to decline, he notes. In that case, the reduced value of the lower-quality nuts may not cover the extras costs of a second shake.
“Also,” Beede says, “it puts pressure on processors to handle poorer quality nuts in a way that doesn’t create quality problems for the industry.”
Growers who rely on a custom harvester, have a crop that is fairly uniform in maturity, or who have a lighter crop are probably better off harvesting the pistachios conventionally with just one shake, Beede says.