University of Illinois

No. 20/August 8, 1997

Headaches with Spider Mites Continue

In areas of Illinois where the moisture supply still is inadequate, twospotted spider mites are amplifying their impact. Telephone calls continue to come in to our offices regularly. I'm not certain what more we can say about this situation, except to urge people to scout diligently for spider mites and symptoms of their injury and diagnose the problem accurately. Money can be lost in two ways: (1) not paying attention to spider mites as their densities increase and their impact flourishes, and (2) spraying a field to control spider mites when the problem is something other than spider mites, for example, soybean cyst nematodes.

Will the spider mite outbreak worsen? By comparison, our difficulties with spider mites this year are nowhere near the magnitude of the problem in 1988. The droughty conditions that exist in localized areas this year are not as extensive as they were then. In addition, the temperatures have not been quite as high. In fact, the recent cool weather might help us out a bit. As I indicated in issue no. 17 (July 18, 1997) of this Bulletin, sustained cool and humid weather enhances the spread of a fungal disease that kills twospotted spider mites.

Again, I urge you to let us know if you experience any control problems. Also let us know if you believe the intensity of spider mite infestations in your area is declining. We hope that as the month of August advances, the weather will work in our favor to alleviate the mite problems.
Kevin Steffey, Extension Entomology, (217)333-6652