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Cutworms are an early-season corn pest and there are numerous species that can cause economic damage. For more information concerning cutworm species identification consider reading Identification of the Most Common Cutworms.
Larvae are black to pale-gray and can be distinguished from similar species by the convex granules on the abdominal segments (Figure 1). Larvae increases in length as they grow from 0.25 inch at 3rd instar growth stage to 2.0 inches at 6th to 7th instar. Damage from 1st to 3rd instar larvae cause “shot-hole” leaf feeding while 4th to 7th instar larvae can cut plants at or below soil level.
Figure 1. Black cutworm.
Damage can be particularly severe in weedy, late-planted corn after a soybean crop and in corn planted in flood plains. In terms of economic damage, black cutworm are the most destructive cutworm species in the Corn Belt and can be found throughout North America. Larvae feed on many host plants including corn, vegetables, cotton, tobacco, and various weed species.
The larvae are pale-gray and translucent with a gray-brown head, bars on the front of the face, and a broad yellow-brown stripe on the back (Figure 2). Small larva pull a leaf into a burrow and eat from the tip to the base. Larger larva cut the leaves/plants just above the ground and drag into a burrow for feeding. Eating habits of black and claybacked cutworms are similar.
Figure 2. Claybacked cutworm. James Kalisch. University of Nebraska.Bugwood.org.
Larvae are pale-gray to brown with a red tinge and a faint, dark V-shaped marking on the back of each abdominal segment (Figure 3). Larvae are 0.25 to 1.25 inches long. Larvae infrequently feed on corn but when they do, they usually nip the ends of young corn leaves and rarely cut or drill into the plant.
This species occurs in southern Canada southward to Utah and then eastward to Virginia. Larvae feed on vegetables, clover, alfalfa, tobacco, wheat, corn, grasses, and broadleaf weeds.
Figure 3. Dingy cutworm. Frank Peairs, Colorado State University. Bugwood.org.
When scouting for cutworm damage look for leaf feeding, wilted plants, and missing plants. Also, confirm larvae presence as they typically hide under crop residue or just below the soil surface and come out at night or overcast days to feed.
Application of postemergence insecticides may be warranted when 6 to 8% of seedlings are cut above the ground or when 2 to 4% of seedlings are cut below ground.2 Refer to local university recommendations for economic thresholds and postemergence insecticides.
Soil applied insecticides at planting may not be economical due to the sporadic infestation nature of cutworms.
Acceleron® Seed Applied Solutions for corn provide control of black cutworm. Also, SmartStax® technology corn products with Acceleron® Seed Applied Solutions with Poncho®/VOTiVO® provide an additional mode of action against black cutworms.
The following managements practices apply to all cutworm species:
Several corn growing states coordinate an adult BCW moth trapping program which is a tool that can be used to predict when more regular field scouting should occur. Presence and frequency of adult moths indicate potential egg-laying activity. A “significant moth flight” is indicated when eight BCW moths are captured during two consecutive nights in a sticky wing trap (Figure 4). An accumulation of 300 (base 50 0F) growing degree days (GDD) is needed from egg-laying to develop BCW larvae large enough to cut corn plants. Scouting should begin after 300 GDDs accumulation from the area’s first spring significant moth flight.1
Figure 4. Winged trap showing lure and eight captured BCW moths.