How Do You Control Spider Mites In Soybeans?

The short answer to the question is, "Not very well."

The question, itself, came up this week in a conversation with Ames Herbert, Virginia Extension Entomologist, who said that he'd received several farmer calls about spider mites in soybeans north of the James River, an area with mostly a corn-soybean rotation, unlike areas to the south that tend to have more cotton and peanuts.

Samples sent to him from infested soybeans contained a large number of adults "and tons of eggs," as Herbert put it.

"We have limited options for treating mites in beans," Herbert said. "The new-generation miticides used in cotton aren’t labeled for soybeans. Brigade and related chemistries are somewhat effective. Dimethoate and Lorsban also are used."

But dimethoate, he added, might be "a little quirky" because it has a pH issue, and water has to be adjusted if the pH is too high. Plus, it has to be stored properly.

"So, make sure you’re using fresh material if that’s your choice, not something that's been in the warehouse for several years," Herbert cautioned.

Lorsban can be effective, he noted, but it has some phytotoxicity issues sometimes.

"The big problem with mites – regardless of the material – is that growers often wait until they’ve got a near-salvage situation, with large numbers of adults, plus eggs," Herbert said. "You can knock out the adults on the first round but still probably have to come back in 5 to 7 days with a second treatment to take out the hatchlings. That’s the only way to break that kind of cycle. It’s a tough, expensive pest and, unfortunately, tends to show up in drier seasons."

Herbert added: "That area (where mites were being found in beans) really isn’t that dry, so this doesn’t bode well for mite problems this season."

- Owen Taylor