Integrated Crop Management

Seed treatments may not stop cutworms

Black cutworms are occasional pests of seedling corn in Iowa. Larvae can easily cut corn through the V4, and sometimes, the V5 stages of growth. Adult moths prefer to lay their eggs in soybean stubble rather than corn stubble, and they are more attracted to fields with winter annual weeds and low-lying wet fields.

Prevention of cutting and stand loss from black cutworms is a goal of many corn farmers. A neonicotinoid insecticide applied to the corn seed prior to planting offers the promise of early-season insect control from this and other insects. The neonicotinoid insecticides, such as Cruiser, Gaucho, and Poncho, are systemic in action, meaning that the chemical is absorbed from the seed coat by the growing seedling and transported to the more actively growing sections of the plant, i.e., new leaves. However, preliminary research conducted at Iowa State last year and this year has found that the low rates of either Cruiser or Poncho were ineffective in preventing cutting by 4th-stage larvae. In contrast, the high rate of Poncho (Poncho 1250, and the only product tested so far at the high rate) has provided very good protection against cutworm injury.

Black cutworm and cut corn plant.

Cornfields that historically have had cutworm problems and were treated with a low rate of any seed treatment should still be scouted for cutworm injury. The low rates of Cruiser and Poncho may not stop cutworm damage.

This article originally appeared on page 76 of the IC-494 (9) -- May 9, 2005 issue.

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