Attribute it to helpful weather, plenty of predatory insects, even good fortune — whatever the reason, Pacific spider mites have caused relatively few problems this season for almond growers in the San Joaquin Valley, demonstrating the benefits of threshold-based sprays for controlling the pest.
“There’s no way to know for sure what all of the contributing factors were,” says David Haviland, University of California Cooperative Extension entomology farm advisor for Kern County.
“The mites showed up early in the season, but even with 100-degree plus temperatures the last two weeks of July, populations didn’t explode. This was despite reduced irrigation on many blocks that, in theory, should have made the trees prone to late-season outbreaks.”
A prolonged, unusually cool spring plus favorable weather continuing through the first half of July minimized orchard stress, helping to keep mites in check. The pest thrives on stressed trees.
Even when the heat did come, it was for relatively short periods, with mild nighttime lows in the 70s. At the same time, a fair number of mite-feeding six-spotted thrips, minute pirate bugs, lacewings and mite destroyer beetles also helped limit the spread of the pest.
Some growers felt a miticide was necessary at hull split, while others sprayed just to be sure, Haviland says. But, many skipped a miticide in their hull split sprays altogether.
“It was refreshing to see how well miticides in May and June held up and that, in many cases, the beneficials took care of things from there.” he says.
As a result, this season has highlighted the value of threshold-based spraying as a viable mite control option for almond growers.
“For several years, we’ve been advising producers to forego calendar-based preventive miticide treatments in May and at hull split,” Haviland says. “This is the first year that a lot of them did that. They were willing to wait until they saw mites before spraying. Of those I have talked to, growers who used threshold-based programs saw no defoliation, and many got away with a one-spray program.”