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College of Food, Agricultural, and Environmental Sciences


Continued Dry Conditions May Favor Spider Mites

July 22, 2002

WOOSTER, Ohio - Continuing drought conditions through much of Ohio may lead to outbreaks of two-spotted spider mites on soybeans.

Ron Hammond, an Ohio State University entomologist with the Ohio Agricultural Research and Development Center, said that growers should be scouting their fields now for adult mites and eggs and spider mite injury.

"Some fields in Ohio haven't had any rain since early June," said Hammond. "Growers need to be on top of what's happening in their fields and need to be aware that if we don't get sufficient rain soon there is the potential for spider mite outbreaks." The two-spotted spider mite feeds on the sap of the soybean plant causing injury. Large spider mite populations, running in the tens of thousands per plant, are enough to kill the crop, causing significant yield losses.

"We are starting to find small numbers of spider mites in fields now and they could build up to heavy populations if this drought continues," said Hammond. He added, however, that spider mite populations could be a lot worse if it hadn't been for the wet spring. "The rains we got in the spring helped keep early populations down, so for as dry as it's been, it isn't as bad as it could be," he said.

Yellow/bronze discoloration of plants along field edges or within in a field is characteristic of spider mite feeding, said Hammond. "Outbreaks can occur not only along field edges, but within in a field itself, so growers should make sure their entire field is scouted," he said. "If growers are finding large populations of adults and eggs on the underside of the leaflets, then treatment is probably warranted." Growers should also be scouting their fields right now for the soybean aphid, which was found in Ohio fields two weeks ago. Low populations of the insect have been discovered so far, to the delight of Ohio State entomologists who were anticipating high numbers.

"We are more concerned about the spider mite right now than the soybean aphid," said Hammond.

Candace Pollock
Ron Hammond