Black Cutworm

Bryan Jensen, UW Extension and IPM Program

A friendly reminder regarding the potential for Black Cutworm (BCW) damage in corn. Based on arrival of the migrating adults, the WI Department of Agriculture, Trade and Consumer Protection’s Pest Survey is anticipating BCW cutting may appear around May 21. Although BCW’s are an occasional pest in Wisconsin, the Pest Survey’s BCW pheromone trap network had recorded a strong flight this spring. Furthermore, a lot of Wisconsin’s corn will likely be at a stage (VE-V4) which is susceptible to cutting and/or below ground tunneling.

Begin spot checking corn fields that will be most attractive and include fields with significant broadleaf weed populations, soybean residue and/or low lying areas of fields. To get an accurate assessment of BCW damage, count the number of cut plants in 50 consecutive plants in each of 5 areas of a field and collect 10 larvae to determine instar. Treatment is suggested when 2-5% of the plants are cut and before the later instars (roughly 1 inch) are present. Some seed treatments and Bt hybrids may control/suppress black cutworms. However, when BCW populations are high these treatments may not control cutworms effectively. Knowing the size of larvae is important and a head capsule gauge can be found in on page 56 (Table 2-9) of A3646, Pest Management in WI Field Crops. For example, if the majority of larvae are 7th instar, feeding may only continue for another 5 days making control uneconomical. If damage is not uniform within a field, spot treatments may be a good option.

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