Tips For Balancing Almond Mites And Predators
May 16, 2016 Almond growers need to do a delicate dance to keep spider mite populations down, but not so far that beneficial predators pick up and move on.
David Haviland, farm advisor with University of California Cooperative Extension in Kern County, says growers should monitor orchards weekly to keep tabs on the populations of both pacific spider mites and two-spotted spider mites, as well as their predators, such as six-spotted thrips. Those mites can be controlled through pesticide sprays, but overdoing it can lead to a loss of those beneficial pests.
“If it weren’t for beneficial insects, every almond tree in California would be defoliated by spider mites,” Haviland says. “It truly does require an ecology-minded person to keep track of what’s going on out there.”
Pest control advisors should weekly collect 15 leaves per tree from about five trees in an area. In general, Haviland says those trees should be treated with a miticide if:
- One-quarter of the leaves have mites and no predators present.
- One-third of the leaves have mites and only a few predators.
Hold off treating if 25% of the leaves have mites and some predators present, he says.
“There’s a tricky balance there. If you never have any mites, there’s never any food for the mite predators to get established on,” Haviland says. “There’s a benefit of having some mites out there.”
During the growing season, the two mites that are most prevalent are the Pacific spider mite (Tetranychus pacificus) that is most common in the south and twospotted spider mite (Tetranychus urticae) that is most common in the north. Colors range from yellow to green to black. Early in the season, they’re found in the lower to the central part of the tree, but from June to September, eggs are laid on foliage.
If populations rise, it can lead to defoliation.
Haviland says one to two miticide applications per year is standard. Most miticides are effective on spider mites and have minimal impacts on mite predators. The one exception is abamectin, which should be used cautiously or avoided if sixspotted thrips are present in the orchard.
In their efforts to maintain predators, growers should also avoid the use of broad spectrum insecticides for other pests like navel orangeworm, peach twig borer and leaffooted bug. Growers that allow predators to get established and then use miticides only when needed can be successful at managing spider mites.
Growers and PCAs can get more information about scouting and control at the University of California Agriculture and Natural Resources Integrated Pest Management Program page dedicated to spider mites.
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