During 2005, Beede says trial applications made at 20 percent to 30 percent bloom and applications made at 60 percent to 70 percent bloom yielded similar results. But 2005 also had an unusually cool, wet spring that prolonged Serr bloom.
Equally critical for best results are application rates and coverage. This season, Beede and Grant recommend one 11.7-ounce water-soluble pouch per 100 to 200 gallons of water per acre. That equates to 125 parts per million of the active ingredient.
Valent does not recommend adding an adjuvant or tankmixing ReTain with other products, such as copper for walnut blight, says Tom DeWitt, Valent field market development manager in Fresno, Calif. That may change after company researchers conduct trials this season examining the PGR’s compatibility with other chemicals.
To ensure adequate spray coverage, tractors pulling spray rigs should drive between 1.75 and 2 mph.
“All bets are off if you’re applying this product faster than 2 mph,” Beede says. “If you go slower [than 2 mph], you’ll get even better coverage and even better results. This is about this product hitting the flowers.
“It won’t pole vault in, it won’t be carried in by ants and it won’t translocate, so it has to be on target,” he says.
Beede also recommends against spraying in the wind or rain because the product has to hit the flowers.
With no data on aerial applications, Beede says neither he nor Grant is comfortable advising ReTain’s use by air. They plan this season to conduct trials involving aerial application.
In addition, Valent researchers plan to conduct trials with Beede and Grant on Chandlers, since that variety also suffers from PFA,albeit to a much lesser extent than Serrs, DeWitt says.
Changing other cultural practices
Because ReTain should significantly increase yields, DeWitt says growers may need to prune trees to avoid limb breakage caused by a heavier nut load. They also may need to modify irrigation and fertilizer because of the larger crop.
To find out how the PGR will perform under your cultural practices, the farm advisors suggest experimenting with it on a small block of Serrs with the worst PFA problems – perhaps an orchard abutting one with Chicos, Vinas or Chandlers that shed an overabundance of pollen.