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Infestations of twospotted spider mites continue to plague soybean producers in several of the drier areas of the state. We first reported on these pests in issue no. 9 (May 25, 2001) of the Bulletin when they were observed infesting clover in southern Illinois. As we suggested, these first sightings of mites in clover might serve as an early indicator of future problems with these pests in soybeans. Well, for the persistently dry areas of Illinois, twospotted spider mites continue to be an aggravation. In issue no. 15 (July 6, 2001) of the Bulletin, we continued to report on sporadic mite infestations in southern Illinois. As Kevin Steffey indicated, treatment guidelines for twospotted spider mites are not based on extensive research. He suggested that a miticide may be warranted if 20 to 25% (prior to pod set) of soybean plants are discolored and mites are present. After pod set, a treatment may be warranted if 10 to 15% of plants are discolored. Products suggested for control of twospotted spider mites in soybeans are dimethoate (see product label for rate) and Lorsban 4E at 1/2 to 1 pt of product per acre. The use of Lorsban 4E is restricted to certified applicators. Many producers in the northwestern sector of Illinois are finding soybean aphids and twospotted spider mites in their soybean fields. For a more complete discussion of this topic, please refer to last week's Bulletin (no. 17, July 20, 2001). As we've discussed many times before, mite densities will continue to explode in drought-stressed soybean fields. Treating border rows may be a cost-effective management approach instead of spraying entire fields; however, in 1988, as the drought extended, many producers eventually treated entire fields (sometimes twice). Let's hope we see some rain.--Mike Gray
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