While nature can impose challenges on our growing season, it occasionally offers a gift. One of these gifts comes in a tiny, translucent package, with a ravenous appetite for spider mites — the six-spotted thrips. How can almond growers take advantage of this acrimonious relationship between spider mites and six-spotted thrips, potentially reducing pesticide use and costs along the way?
Six-spotted thrips are not only effective for mite management but also provide a number of operational benefits. (Photo credit: Jack Kelly Clark, courtesy University of California Statewide IPM Program)
With funding help from Almond Board of California, David Haviland, University of California Cooperative Extension (UCCE) entomology farm advisor, has been researching biological controls of spider mites. His advice is straightforward.
“Don’t starve them and don’t kill them,” said Haviland. “It’s important to treat before mite outbreaks occur, but wait to treat until it becomes necessary. Treat too early, and you’ll interrupt the balance by starving predators like the six-spotted thrips. If you wait too long, especially when bio controls aren’t present, you could have a full-on mite problem within a few weeks.”
The practice of early season preventive sprays for spider mites has been common for many years, but changes in thrips populations over time have made prophylactic sprays unnecessary and actually damaging to a balanced, integrated program. Prophylactic early season sprays often prompt pest mite flare-ups. First, they are toxic to predators, and second, they wipe out existing low-level spider mite populations so predators starve. Instead, the Almond Board and Haviland recommend that growers monitor and spray only if spider mites exceed a 25-40% infestation threshold.
Guidelines on presence-absence leaf sampling are given at the UC Statewide IPM website. As a matter of efficiency, monitoring should be done weekly, but detailed recordkeeping using the sample forms need not start until a “treat-no-treat” decision appears to be emerging.
“If 25% of leaves sampled have mites but there are no predators present, you should apply a miticide treatment,” said Haviland. “If predators are present, hold off on treatments and continue monitoring their progress in controlling mites, applying a treatment only if you see 40% of leaves infested.”
Weekly monitoring using presence-absence sampling is recommended for keeping tabs on mite and thrips populations. Check leaves for mites, and use a sticky card to monitor for the presence of six-spotted thrips. Haviland’s research found that yellow 3x5 sticky cards* attached with simple binder clips and hooked to trees with unwound large paper clips were the most effective way to monitor for thrips.
Haviland also reminds growers that cultural practices, such as keeping trees healthy and minimizing dust, are year-round efforts that can help curb spider mite population growth.
“Relying on six-spotted thrips for mite management is not only effective but provides a number of operational benefits. They occur naturally, and they’re free, with no residues, Pre-Harvest Intervals, permits or worker safety issues to worry about,” said Haviland. “Miticides are absolutely important for managing outbreaks, but predators can help suppress mite populations, providing a buffer against catastrophe.”
*Available online through Great Lakes IPM.
