New Predatory Species May Help Manage the Pest

 By Patrick Cavanaugh, Editor

Two-spotted mites in strawberries continue to be one of the biggest problems every year.

“We see more of it coming from the nurseries, and this year is no exception,” explained David Peck, COO and Farmer of Manzanita Berry Farms in Santa Maria.

“What’s interesting to me is that in the years that we’ve been using persimilis predator mite, and that has been since the early ’80s, we don’t see the persimilis taking over two-spot populations as early in the season as we used to,” Peck continued. “Whether that’s weather-related, humidity-related, or if there’s a change in the genetics of the commercially available persimilis, I don’t know.”

David Peck

Peck said growers need to be aware of another trouble mite, the Lewis mite.  Lewis mites have been seen on strawberries and raspberries in the Ventura area for some time, but growers appear to be noticing increased infestations in the recent years.  Some growers have also seen them in Santa Maria in recent years, but they have so far not been reported from the Watsonville area.  Considering the recent trend, growers might keep them in mind while scouting for pests.

“They’re out there, some places greater than others. Persimilis don’t like to eat Lewis mite. They are susceptible to all the same miticides. However, if you are relying heavily, on biologicals, you got to know if you have Lewis mite,” Peck said.

“I add fallacis predatory mites early in the season as a preventative for Lewis mite. The fallacis will eat two-spot or Lewis mite equally well and have done a pretty good job of keeping that initial early-season population of both mite species under control,” he explained.

Peck said that if there are mites in the strawberry nurseries, and the nurseries do not want to spray miticides, he understands that due to the possible development of pesticide-resistant mites showing up with plants.

“That’s a valid reason not to spray miticides at the nursery level. But there’s good data that fallacis will exist in those Northern California strawberry nursery areas, and they’re actually less expensive to procure than persimilis, and they survive through a wider environmental range than persimilis. They can handle colder, dryer, and hotter,” Peck said.

Some of the best data on strawberries and raspberries come out of Oregon State. It shows numerical data on how to put out the predatory mites, including how few you can put out.

“Personally, I’d be willing to spend an extra 50 cents or a dollar a thousand if the nurseries would inoculate their fields with fallacis. You might get a few predators coming in with your plants,” he said.

There is additional research on fallacis versus another predatory mite known as andersoni. Data shows that andersoni may be stronger than fallacis, thus doing a better job at controlling two-spotted mites.

Peck said that he has used andersoni on a test basis.

“I did not have enough of the predator to thoroughly complete a test in our organic fields, but I’m thinking that I will use that species for early season mite control.”