The data also showed similar results between orchards in the Tulare County area and orchards farther north in San Joaquin County.
In one of Grant’s 2005 whole-tree studies, he found that ReTain-treated trees had 82.6 percent flower set, whereas untreated trees had only 30.8 percent flower set. The additional flower set translated into a per-acre yield of 4,816 pounds for the treated trees and 2,972 pounds for the untreated trees.
Despite his results, Grant says he doesn’t want Serr growers to rush out and apply the product until they determine what is causing their low yields.
Grant says growers should ask themselves, “Is it PFA? Is it Phytophthora or nematodes? Before they make this big expensive application, they need to have some level of confidence that the lack of production is due to PFA. It’s usually the case, but this is just an extra step in the process.”
Although Beede says he doesn’t know how much Valent or agricultural chemical dealers will charge, he thinks the PGR will provide growers a strong return on investment.
“If these guys get a 1,000- to 1,200-pound increase in walnuts at 80 cents per pound, that’s an $800 to $1,000 improvement in income,” Beede says. “Although the product won’t be cheap, it will be worth it if they do it right.”
Timing and spray coverage is critical
To obtain results similar to theirs, Beede says you’ll need to correctly assess the bloom stage.
“If there’s anything that is the single biggest challenge in applying this product, it’s having farmers make accurate estimates of what percentage of bloom is actually present in their orchard,” Beede says. ”This product will require walnut orchardists to put on their boots and get out in the field and personally observe what’s going on relative to the bloom.”
This is complicated because the tops of some trees may be at 100 percent bloom while branches in the shade or weak spurs on the same trees haven’t begun to bloom yet.
Although Beede says growers should target 30 percent bloom, three years of field trials show there is some leeway.
Chilling hours also will affect bloom, Beede says. If trees receive less than the optimum 800 to 850 hours of chilling temperatures, blooms tend to be more strung out, making it more difficult to determine proper spray time.