Black cutworms in wet and dry soils

It has been a fairly wet spring in many parts of Iowa and the black cutworms seem to be "enjoying" the moist soils. A question has been raised about the behavior of black cutworms during this cooler and wetter spring. Are there any differences, and if so, how might the wet soils and cutting by cutworms affect corn growth and development?

Bill Showers, USDA entomologist (retired), published a brief report in 1983 regarding some of his research in Iowa. He measured cutworm activity during a dry spring (3.8 inches of rain during the plant growth stages attacked by the larvae) and two wet springs (10.8-11.2 inches). The study showed "that when the soil is dry, black cutworms feed 5-8 centimeters (2-3 inches) below the soil surface and that all cutting occurred below the stem tip (growing point) of the corn seedling.

The effect of dryness on the capacity of black cutworm to inflict potential yield loss is evident during the coleoptile growth stage. Although there was significantly more cutting by black cutworm during a wet spring, the increased amounts of moisture during the coleoptile growth stage precluded some of the black cutworm larvae from cutting below the growing point of the plants. Therefore, because of the nature of the cut and the presence of adequate moisture, many of the cut plants recovered, matured, and produced grain. Essentially, 60 percent cutting in a dry spring affected the potential yield nearly as much as 87 percent cutting in a wet spring."

Basically what this means is that during a wet spring black cutworms may cut more plants but the impact on yield is less severe because the plants recover better than plants in drier soils. The research did not address the effects of soil or air temperatures on black cutworm cutting behavior.

This article originally appeared on page 109 of the IC-486(13) -- June 11, 2001 issue.

Updated 06/10/2001 - 1:00pm