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Identifying Cutworm Larvae Accurately Will Become Important Soon

April 19, 2002
Although most of the attention on cutworms focuses on the black cutworm, Agrotis ipsilon, a few other species of cutworms also can be found in cornfields. Although some of these other species can damage corn, others cause very little, if any, economic damage. Consequently, it's important to be able to distinguish among the species you find so that accurate control decisions (including a decision not to apply an insecticide) can be made. As I indicated in last week's Bulletin (issue no. 3, April 12, 2002), excellent photos of a few cutworm species can be found in an issue of Iowa State University's Integrated Crop Management newsletter at icm/2000/5-8-2000/cutworm2000.html. Following is some information about a few of the species of cutworms that are found in Illinois (excluding the black cutworm, discussed elsewhere).

Claybacked cutworm, Agrotis gladiaria. We haven't seen many claybacked cutworms in recent years, but when they occur, they can be just as destructive as black cutworms. Because they overwinter as partly-grown larvae, claybacked cutworms can cause significant damage early in the spring. Their feeding habits and appearance are similar to those of black cutworms. A broad, yellow-brown stripe on the back of the larva explains the common name of this cutworm. The rest of the body is pale gray and translucent, and the head is gray-brown with bars on the front of the face. A full-grown larva is 1 1/3 inches long.

Dingy cutworm, Feltia ducens. Dingy cutworms are common in Illinois, and they frequently are mistaken for black cutworms. However, they rarely cause economic damage to corn. Like clay-backed cutworms, dingy cutworms overwinter as partially grown larvae, so fourth instars often are present in cornfields at planting time, particularly in weedy fields or in corn planted into pasture or alfalfa. Dingy cutworm larvae are pale gray to brown, tinged with red. A faint, dark V-shaped marking appears on the back of each abdominal segment. The head is pale brown-gray. Tubercles (knotlike protuberances) along the top of the abdominal segments are equal in size (on the same segment), in contrast to the unequal-sized tubercles on the back of the black cutworm. Tubercles become larger toward the posterior segment.

A few people have discovered dingy cutworms already this spring, so be aware of the differences between dingy and black cutworms. Accurate identification could save someone some money.

Glassy cutworm, Apamea devastator. The glassy cutworm prefers sod as a host, so it is more often a pest in crops planted after sod or pasture. It constructs subterranean burrows to feed on underground portions of host plants, including corn. This species also overwinters as a larva. The glassy cutworm has a green-white body that appears translucent or glassy. Full-grown larvae are 1 1/2 inches long.

Sandhill cutworm, Euxoa detersa. This species of cutworm can be very destructive in fields planted in sandy soils. Like glassy cutworms, sandhill cutworms construct subterranean burrows to feed on underground portions of host plants. This species overwinters as a partially grown larva. The larva is white to pale gray. Pulsations in the blood vessel along the back can be seen through the cuticle ("skin"). Faint, chalky-white stripes are evident on the back and sides, and the head is dull red-brown. A full-grown larva is about 1 1/3 inches long.

Variegated cutworm, Peridroma saucia. This pest caused quite a bit of damage in some soybean fields in Illinois in 2001, often being mistaken for armyworms. It also is found in cornfields, although it seldom causes serious economic damage. Like black cutworms, variegated cutworms do not overwinter in Illlinois. The moths fly into the Midwest during the spring. Females deposit eggs in pastures; fencerow grasses; low, densely growing weeds; and debris in fields that have not been tilled. Larvae develop through six instars, feeding primarily at night. The caterpillar's color varies considerably. However, a narrow line of pale yellow dots along the middle of the back is almost always present. A full-grown larva is 1 1/2 inches long.

Variegated cutworm larva with a few pale yellow dots evident on its back.

Happy cutworm hunting! Let us know what you find as you begin to scout corn for signs of early-season insect injury.--Kevin Steffey

Author: Kevin Steffey

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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