Beet Armyworm (Spodoptera exigua)
Bertha Armyworm (Mamestra configurata)
Western Yellowstriped Armyworm (Spodoptera praefica)

Description

Adult: Armyworm moths have a wingspan of about 1.25-1.5 inches and are mottled gray and brown in color with gray or tan colored markings depending on the species.
Egg: Beet armyworm eggs are pale green to pink, ridged, and are found in a mass covered with gray cotton-like material.
Larva: Armyworm larvae are about 1.25-1.5 inches long and range in color from olive green, light green, and yellow, gray with dark markings, and yellow with dark gray or black markings. Pupa: Armyworm pupae are about 0.75 inch long and reddish-brown in color

Life History

Armyworms overwinter as pupae in the soil. Adult moths emerge from March to July to mate and lay eggs. Hatched larvae feed for 5 to 8 weeks before pupating in the soil. There are two generations each year. Larval feeding from the second generation may be seen until early October before larvae enter the pupal stage to overwinter.

Damage

Armyworm larvae feed in colonies and cause skeletonized leaves. As they grow, they are more likely to feed on entire leaves or cause irregular patches of feeding damage.

Beet Armyworm (John Capinera, University of Florida, Bugwood.org)
Beet armyworm (John Capinera, University of Florida, Bugwood.org)

Bertha Armyworm (David Gent, USDA Agricultural Research Service, Bugwood.org)
Bertha Armyworm (David Gent, USDA Agricultural Research Service, Bugwood.org)

Western Yellowstriped Armyworm
Western Yellowstriped Armyworm

 

Black Cutworm (Agrotis ipsilon)
Variegated Cutworm (Peridroma saucia)

Description

Adult: Cutworm moths are brown or dark gray with front wings that have irregular bands or spots and lighter-colored hind wings. Average wingspan ranges from 1.25 to 2.12 inches.
Egg: Extremely small spherical eggs are white or pale yellow when first laid, changing to brown before hatching. Depending on the species, eggs are laid singly or in irregular clusters of 30-360 eggs on leaves or stems, or near the base of the plant.
Larva: Dull gray to brown caterpillars with black stripes or spots, and up to 2 inches long when full grown. Most cutworms curl into a “C” shape when disturbed and during the day, are usually found in dirt clods or just below the soil surface.
Pupa: Dark brown to orange in color with two spines on one end. About 0.75 inch long.

Life History

Cutworms overwinter as larvae in the soil or under plant debris. In the spring, larvae begin to feed on roots and plant stems. They then pupate in the soil and emerge as adults. Female moths lay eggs on the undersides of leaves and hatched larvae feed on plant foliage, and then pupate in the soil. Both black and variegated cutworms have a second generation (or more during hotter seasons). Larvae that hatch from later generations feed until the weather cools and then enter the soil for overwintering.

Damage

Cutworms feed on a wide range of crops including potato, winter wheat, corn, tobacco, asparagus, bean, beet, cabbage, castor bean, grape, lettuce, peanut, pepper, radish, spinach, squash, strawberry and tomato. Most cutworm damage occurs during spring and early summer. Cutworm larvae feed at the soil surface and may cut off the stems of young plants during stand establishment. Later in the season, some species feed on plant foliage which may cause wilting and possible defoliation when infestations are high.

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Black Cutworm
Black Cutworm (Roger Schmidt, University of Wisconsin-Madison, Bugwood.org)

 

Variegated Cutworm (James Kalisch, University of Nebraska, Bugwood.org)
Variegated Cutworm (James Kalisch, University of Nebraska, Bugwood.org)

Armyworm & Cutworm Monitoring

  • Conduct regular scouting for larvae and damage. Monitor early, when seedlings emerge, to detect cutworms when larvae are small. Young larvae are easier to control. Cutworms are more commonly found in fields that are planted late, or infested with weeds. When injured plants are found, dig about 1-inch-deep around the base of plants to see if live cutworms are present. Look for wilted plants that may indicate stem feeding injury. Later in the season, monitor plants for foliage damage.
  • For black cutworms, use pheromone traps. A threshold of 2 black cutworm moths per trap per day indicates significant egg-laying pressure. Increase field scouting efforts during crop emergence when threshold numbers are met or exceeded.

Armyworm & Cutworm Management

Cultural

Weedy fields and field borders, and high levels of plant residue provide food sources for armyworms and cutworms. Thoroughly till crop residues and control weeds to reduce armyworm and cutworm overwintering and feeding sites. Remove cool-season weeds along field edges to starve young caterpillars. Lambsquarters and wild mustards are attractive plants for egg-laying. Fall tillage can also help destroy or expose overwintering pupae.

Mechanical

In small-scale vegetable production, protect seedlings with collars made from plastic or Styrofoam cups, or toilet paper rolls cut to size.

Biological

Many predators, parasites, and diseases attack armyworms and cutworms, but because armyworms and cutworms dwell beneath the soil surface, few of these natural enemies are effective in controlling their populations. Bacillus thuringiensis (Bt) products can be effective in controlling young armyworm and cutworm larvae.

Chemical

The sporadic occurrence of armyworm and cutworm infestations typically doesn’t support the use of soil insecticides; however, chronic infestations may require an insecticide incorporated at planting. Alternatively, foliar applications in the spring can protect young plants since larvae at the soil surface will feed on foliage at night.

For cutworms, consider treatment options when thresholds reach 2 cuts per 100 seedlings, and 3-7 cuts for older plants (the older the plant the higher the threshold).