Are Cutworms Causing Damage in Your Fields?

Cutworms are a sporadic early-season pest in corn. Young cutworm larvae may chew small holes into corn leaves, while older larvae are capable of clipping plants at the soil line. Cutworm damage can be minor to severe and go unnoticed until corn seedlings are found dead. There are several cutworm species, each of which varies in primary geographies and life cycles.

For more information on identification of cutworm species refer to the Agronomy ADVICE: Identification of Cutworms.

Management for all cutworms is similar regardless of the cutworm species. The most common and destructive cutworm species found in corn are:

Black Cutworm can be found throughout North America and are considered the most important species in terms of economic damage to corn. Larvae vary in size from 1/8-inch to 2 inches. They are black-pale gray with a greasy-appearing texture and convex granules on the abdominal segments (Figure 1).3 This pest is likely to occur in late-planted corn fields that are weedy, no-till, and/or adjacent to areas of permanent vegetation. Host plants include corn, vegetables, cotton, tobacco, and weed species. 

Figure 1. Black cutworm next to clipped corn plant.
Figure 2. Claybacked cutworm. James Kalisch, University of Nebraska, Bugwood.org.

Claybacked Cutworm occurs in the north-central and eastern United States. Larvae are pale gray and translucent with a gray-brown head and bars on the front of the face (Figure 2). Their back has a broad yellow-brown stripe. Small larva can pull the leaf down into a burrow and eat the leaf from tip to the base, while larger larva cut the leaves or plants just above the ground and drag them into a burrow to continue the feeding.

Dingy Cutworm is found in southern Canada, extending south to Utah larvae, then eastward to Virginia. Dingy cutworms are pale gray to reddish brown with gray, V-shaped markings on the back of each segment. Mature larvae are about 1-inch long. Host plants include vegetables, clover, alfalfa, wheat, corn, grasses, and broadleaf weeds. When this cutworm feeds on corn it usually nips the ends of young corn leaves.

Figure 3. Dingy cutworm. Frank Peairs, Colorado State University. Bugwood.org.
Trapping Adults and Management Options

Adult cutworm moths can be used to determine the potential threat posed by some species. Several corn-growing states have a black cutworm trapping program. A significant flight is indicated when eight adult males are captured in a two-night period. The date of this capture is used to predict larval development and the date when feeding may begin. Scouting for damaged seedlings should begin when 300 growing degree units (GDU) have accumulated after a significant moth trap capture.2 Fields with early-season weeds or vegetation are at the highest risk for cutworms, so these fields should be scouted first. When scouting for cutworm, look for leaf damage, wilted plants, or plants that are cut at or near the soil surface.

Because of the irregular distribution in geography and time, cutworms continue to be a challenging pest to control. Cultural practices that apply to all cutworm species include removing winter annual weeds prior to planting, and rotation to a non-susceptible crop, especially after a long-standing pasture or meadow. 

How to Control Cutworms in Corn

Typical treatment threshold levels for cutworms occur when 6 to 8% of seedlings are cut above ground, or 2 to 4% of seedlings are cut below ground. Refer to your local university Extension guidelines for treatment thresholds.

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.

In summary, cutworms are the larvae (caterpillars) of several species of night-flying moths that can feed on a wide range of cultivated and wild plants. Although some species can cause damage, others may cause very little, if any, economic damage. Managing cutworms requires regular monitoring, scouting, vegetation control before planting, and avoiding fields with a history of cutworm problems.

More information on cutworms and other insect pests in corn, refer to  Early-Season Insects in Corn.

Sources:

1 Hein, G.L., Campbell, J.B., Danielson, S.D., and Kalisch, J. 1993. Management of the army cutworm and pale western cutworm. G1145. University of Nebraska Extension.

2 Bailey, W. Black cutworm monitoring and forecasting program. University of Missouri.

3 Black Cutworm. Purdue University. https://extension.entm.purdue.edu

4 Steffy, K., Rice, M., Andow, D., Gray, M., and Van Duyn, J. 1999. Handbook of corn insects. Entomology Society of America. 5 Peairs, F.B. 2010. Caterpillars in small grains. Colorado State University Extension.

Web sources verified 2/9/18

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