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College of Food, Agricultural, and Environmental Sciences


Early Appearance of Twospotted Spider Mites Could Damage Ohio Soybean Crops

June 18, 2012

WOOSTER, Ohio – The early and prolonged period of dry, hot days Ohio has experienced so far this spring is causing an early appearance of the twospotted spider mite, a dangerous pest that can cause severe damage to soybean crops, including the death of the entire plant, an Ohio State University Extension entomologist said.

Some growers have already reported finding twospotted spider mites on soybeans, which have the potential to cause yield loss for soybean crops, said Ron Hammond, who also has an appointment with the Ohio Agricultural Research and Development Center.

In fact, the concern about these pests, which are appearing in crops at least a month and a half earlier than normal, is so strong that growers are being cautioned to scout their fields and take action if they see evidence of twospotted spider mites in their fields, he said.

“Twospotted spider mites have the potential to cause more yield loss than any other insect,” Hammond said. “The damage caused by the mites is severe enough to kill the entire plant.

“Growers who have a bad infestation will not see any yield from the affected area. While it doesn’t happen very often, in those areas where it does, the effects are devastating.”

Typically Ohio growers aren’t impacted by twospotted spider mites until late July or early August, because moisture levels in spring and early summer are usually high enough to keep the pests at bay, Hammond said. The dry, hot summer days typical of July and August are when conditions are conducive to spider mite infestations. But during that time, the spider mites are typically found only along the edges of a soybean crop and cause minimal damage, he said.

But the early hot, dry conditions and low soil moisture levels [that growers are experiencing statewide are causing the pests to appear earlier and, because soybean plants are short in height, the pests have more potential to impact entire fields instead of just the edges, Hammond said.

“If we were having normal rainfall, we wouldn’t be worried about mites right now,” he said. “In some parts of the state, soils are very dry and crops are starting to suffer.

“We’re just in the middle of June and already dealing with this situation, so the concern is what will happen in the coming weeks, considering that the weather outlook calls for continued hot, dry conditions.”

Over 50 percent of the state is experiencing moisture levels in the short to very short category for topsoil right now, according to the latest U.S. Department of Agriculture weekly crop report, said Joe Cornely, spokesman for the Ohio Farm Bureau.

“Moisture levels are declining because we’re just not getting any rain,” he said. “It’s dry in a big area of the state and not much rain is forecast for at least another week to 10 days.

“It’s dry now and going to get dryer, and that can make growers very nervous.”

Hammond said growers should begin scouting their fields for twospotted spider mites as soon as possible.

Spider mites infestations can first be noticed by yellow stippling on the upper surface of the leaves, he said. The mites themselves, which are found on the underside of the leaves, can be identified using a good hand lens. 

Growers can find more information on when they should spray for twospotted spider mites and other treatment guidelines at

At this time of year, mite infestations might be found not only on field edges, but also throughout the field,” Hammond said. “The earlier you recognize mite infestations, the quicker you can deal with them prior to economic losses.”

Tracy Turner
Ron Hammond