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College of Food, Agricultural, and Environmental Sciences


Dry Weather Inviting Soybean Pests

September 3, 2008

WOOSTER, Ohio -- Abnormally dry conditions continue to plague Ohio, and lack of rain has been inviting pest problems for the state's soybean crop.


Two-spotted spider mites become active when fields are dry, and Ohio State University Extension entomologists have reported some outbreaks, especially along field edges. 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 reported a few weeks ago that two-spotted spider mite problems were beginning to occur in dry areas around Ohio, and the incidence of mites has increased in the state," said Ron Hammond, an OSU Extension entomologist. "We continue to think that they will not become whole field infestations, although growers should nevertheless check areas within their fields. This is especially important on late-maturing soybeans that were planted late and are still green. Those fields that are starting to yellow are probably past the stage where spraying for mites would be recommended."

Yellow/bronze discoloration of plants along field edges or within in a field is characteristic of spider mite feeding, said Hammond.

"If growers are finding large populations of adults and eggs on the underside of the leaflets, then treatment is probably warranted," said Hammond, who also holds an appointment with the Ohio Agricultural Research and Development Center. "If mites have built up sufficiently along the field borders, growers should make an edge spray. This should give late-planted soybeans enough time to continue to make good yields."

Soybean cyst nematode also does damage to soybeans under drought stress. Deemed the "silent robber of yields," SCN is the No. 2 soybean pest in Ohio, behind Phytophthora sojae, which causes Phytophthora root rot. Soybean cyst nematodes feed on the roots of young plants, which prevents the roots from taking up vital nutrients. The result is a drop in yields and subsequent economic losses.

Anne Dorrance, an OARDC plant pathologist, urges growers to scout their fields for potential SCN populations.

"Where the soybeans are shorter and have fewer pods is a great place to check for SCN on the roots," said Dorrance, who also holds an OSU Extension appointment. "Dig up the soybeans and shake off the soil, then look for the females. They appear as tiny white pearls, which glisten on the roots." Notes should be taken and those fields should be sampled in the fall for egg counts through laboratory tests.

"A good accurate egg count in the fall is the first step in soybean cyst nematode management," said Dorrance. "The best management practice is crop rotation, crop rotation, crop rotation. Once the insect is present, you can't get rid of it."

According to the Ohio Agricultural Statistics Service, 78 percent of the soybean crop is in fair to excellent condition. For more information on Ohio's soybean crop, log on to OSU Extension's Agronomic Crops Team Web site at


Candace Pollock
Anne Dorrance, Ron Hammond