The two primary pest concerns in soybeans in Illinois right now are twospotted spider mites and soybean aphids, says Kevin Steffey, University of Illinois Extension.

The mites have been building in drought-stricken areas for weeks, and economic infestations are becoming more widespread. Both central and northern Illinois counties are affected. In northern Illinois, after a couple of weeks of slow development in June, soybean aphid population densities have increased noticeably during the first half of July. Other insects also are showing up in soybean fields, so it seems appropriate to provide an overview of all this activity.

If you are reading other states’ weekly newsletters and pest reports, you already know that population densities of soybean aphids have been increasing significantly over the past couple of weeks. Michigan was the first state to experience widespread economic infestations of soybean aphids, and economic infestations are now appearing in Minnesota and Wisconsin. We became aware of above-threshold numbers of soybean aphids in northern Illinois during the week of July 11, and average densities and percentages of plants infested continue to increase in the counties we have surveyed. Increasing numbers of soybean aphids also are being observed in both Indiana and Iowa.

We are receiving increasing reports of economic infestations of twospotted spider mites in areas where drought conditions persist. The most recent (July 12) U.S. Drought Monitor map indicates severe drought in an area extending from central Illinois into north-central and northeastern counties. Reports of infestations of twospotted spider mites are most common from that area.

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