Agronomic Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

Soybean
We found our first Dectes emerging out of the soil on Monday, and a few beetles yesterday hanging out in sunflowers. Other insects present in most fields include green cloverworms, Japanese beetles, bean leaf beetles, and grasshoppers. There has been a report of beet armyworm active in the area. This caterpillar can be distinguished from green cloverworm by the presence of a dark spot above the second pair of true legs. It also prefers pigweed and will often defoliate them. Another unusual situation that came up this week was stand loss in V2-V3 soybean due to black cutworms. Cutworms had clipped plants above and below cotyledons and were concentrated in lower spots in the field. In many ways, it looked like deer browsing, but without hoofprint. Some plant material could also be seen partially dragged into the soil. In the worst affected areas, up to 5 feet of soybeans had been clipped. Moths oviposit in weedy areas, and larvae prefer to hide under the soil during the day. This is another reason to be checking stand regularly, to find odd situations like this early enough to prevent a problem from becoming worse.

Field Corn
Scout field corn as it begins silking for the presence of Japanese beetles and silk clipping. Generally, 2 beetles per ear, silks clipped below ½ inch, and plants less than 50% pollinated warrant an insecticide application. Japanese beetles will also partially defoliate upper leaves. Most of the time, Japanese beetles are confined to field edges, if an insecticide application is used to target them, a border spray should be sufficient.

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