Reports are coming in that black cutworm larvae are cutting corn and even soybeans. We don’t often see cutting in soybeans but two fields in Niagara region were reported today with significant stand loss and a variety of sizes of larvae.
Fields not treated with an insecticide seed treatment or planted with a Bt hybrid containing Cry1F or Vip3A should be scouted every 3-4 days for the next few weeks. Factors that increase field risk include those with pre-plant annual weeds (eg. chickweed, mustards, volunteer wheat, lamb’s-quarters, velvetleaf etc.), cover crops or no-till/reduced till. Delayed burn downs increase the risk of injury, as the larvae feed on the existing plants and weeds while waiting to move over to the corn crop once it emerges. Fields near Lake Erie tend to have more frequent infestations from moths dropping down as soon as they migrate in from the US, but infestations are not exclusive to fields in that area.
Look for pin-holes in leaves and wilting or cut plants above or below ground. Dig around damaged plants to search for cutworms in the soil where they hide during the day. Larvae larger than 2.5 cm are too big to control though some fields may have a range of sizes. Once the corn crop is in the V5 stage, the growing point of the plant is above ground and can tolerate most of the injury and the larger larvae are slowing down in their feeding, only cutting a few more plants before pupating. Foliar insecticide treatments can provide effective control, if applied at threshold and before larvae are larger than 2.5 cm.
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