No. 16 Article 4/July 8, 2005

Reports of Spider Mite Infestations Are Still Occurring

Although most of the significant infestations of twospotted spider mites have occurred in central and east-central Illinois, we have received reports of mite-infested fields in other areas of the state. We expect the reports of infestations to spread as drought conditions prevail. Recent more pleasant temperatures are not as optimal for twospotted spider mites as they are for soybean aphids, but the spider mites haven't gone away. Continued moisture stress in soybean fields will enable spider mites to rob the plants even more.

If you have not already checked soybean fields in your area for the presence of spider mites, I strongly encourage you to begin looking, even if some much-needed rain has fallen recently. The rain will have little direct effect on the spider mites, so they'll still be present. The rain will help the soybeans tolerate the mites a little better, but a return to drought conditions will encourage a buildup of spider mite populations again.

In tilled fields, infestations of twospotted spider mites will occur most likely along the edges of the fields where spider mites have left their overwintering areas for greener pastures, so to speak. Spot-treating these infested areas will prevent the spread of the infestation if the infestation is known to be restricted to the field edges. But as we have stated many times previously, make sure you check the entire field. If mites are generally distributed throughout a soybean field, it's probably only a matter of time before symptoms begin to show up in areas other than field edges.--Kevin Steffey

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