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Extension > Garden > Insects > Managing lawn and turf insects: blade defoliation

Managing lawn and turf insects: blade defoliation

Vera Krischik and Mark Ascerno, University of Minnesota
Reviewed 2009

Figure 10. Sod webworm adult

Ascerno

Figure 10. Sod webworm adult

Figure 11. Sod webworm larvae

Ascerno

Figure 11. Sod webworm larvae

Figure 12. Variegated cutworm

University of Minnesota Entomology

Figure 12. Variegated cutworm

Figure 13. Black cutworm

University of Minnesota Entomology

Figure 13. Black cutworm

Figure 14. Cutworm in ball

Davidson

Figure 14. Cutworm in ball

Figure 15. Armyworm

University of Minnesota Entomology

Figure 15. Armyworm

Sod webworms (Crambus species and Parapediasia species, Family Noctuidae, Order Lepidoptera)

Identification: The adults of sod webworms are frequently called lawn moths. They are light-colored moths, which make short, erratic, darting flights above the turf and are attracted to lights at night (Figure 10). When resting they fold their wings back closely against their bodies, which gives them a very narrow appearance. Also, their heads appear to have a long snout. The moths lay their eggs in the lawn. The older larvae are a dirty white to light brown with darker spots and are about 3/4 inch long with a black head (Figure 11).

Damage, scouting, and management: The larvae feed at night on grass blades. During the day the larvae hide in silk-lined tunnels or burrows at or slightly into the soil surface. Some species damage plant crowns or roots as well as blades. Two generations can occur in Minnesota. Heavy infestations of the second generation may seriously damage large areas of turf. Although webworm adults are commonly seen, larval damage is uncommon in Minnesota. Look for dew sparkling on the webs in the early morning or at dusk. Use the flotation method to force the caterpillars to the surface, where they can be counted. In the flotation method, a soapy solution is poured inside a topless and bottomless can. The soapy solution is made by adding one ounce of mild dishwashing detergent to one gallon of water. It is best to scout for sod webworms in June and again in early August, since sod webworms have two generations per year. Tolerance is around 12 larvae/ft2. Water the lawn thoroughly a day or so before applying an insecticide. Then delay further water for at least three days after treatment.

Cutworms (Family Noctuidae, Order Lepidoptera), Black cutworm (Agrotis ipsilon), Bronze cutworm (Nephelodes minians), Variegated cutworm (Peridroma saucia)

Identification: Full-grown cutworm larvae are about 1-1/2 inches long. The variegated cutworm's color ranges from brown to gray (Figure 12). The black cutworm larvae are dark gray above and light gray below with black dots along the side of the body (Figure 13). The bronze cutworm's color is a mottled burgundy brown. When disturbed cutworms roll into a ball (Figure 14).

Damage, scouting, and management: Black cutworm adults arrive in summer on southerly winds and larvae cannot overwinter in Minnesota. In golf courses, they are often found on greens surrounded by dense rough. The larvae feed on the grass blades or cut the grass off at the soil surface at night. During the day they hide in the soil or under debris. Aeration holes in greens are often utilized by cutworms as burrows. However, the presence of these aeration holes does not increase the number of cutworms. It is possible to have 1-3 generations per year.

Armyworms (Pseudaletia unipunctata, Family Noctuidae, Order Lepidoptera)

Identification: These caterpillars feed on a variety of grasses including agricultural grass crops such as small grains and corn. Turf grasses are not commonly infested. Mature larvae reach 1-1/2 to 2.0 inches in length. Larvae are a dull yellow to gray with stripes running lengthwise along the body (Figure 15).

Damage, scouting, and management: Populations arrive as annual flights from overwintering southern populations. Populations of armyworms are typically kept in check by natural means, though population booms can occur, generally after a drought. Thresholds are not well developed.

Fall armyworm (Spodoptera frugiperda, Family Noctuidae, Order Lepidoptera)

Identification: These caterpillars feed on a variety of grasses. Mature larvae reach 1-1/2 to 2.0 inches in length. Larvae have a black stripe down the middle of the back and on each side; four black dots on the dorsal side of each abdominal segment; and the face with a yellow inverted Y-marking.

Damage, scouting, and management: Populations arrive as annual flights from extreme southern populations. They are similar in size to armyworms. Populations of fall armyworms are typically kept in check by natural means, though population booms can occur, generally after a drought. Thresholds are not well developed.

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