Turfgrass Entomology (cutworms)

Cutworms and armyworms are the larvae (caterpillars) of several species of night-flying moths in the family Noctuidae. Caterpillars in this group are characterized by three pairs of legs situated behind the head, fleshy prolegs and a distinct head. Adults (moths) are robust, drab-colored and hairy with wingspans up to 1 1/2 inches across. Typically, the front wings are darker than the hind wings and have various patterns of light and dark markings. Cutworm and armyworm larvae are only occasional pests of turfgrasses in Nebraska. Adults do no damage to turf.

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The most common turf-infesting species of cutworms are the black cutworm, Agrotis ipsilon, variegated cutworm, Peridroma saucia, and bronzed cutworm, Nephelodes minians, shown in order above. Fully grown larvae reach 1 1/2 inches, with the bronzed cutworm being slightly larger. All species have a dark brown to gray head. The black cutworm is dark gray to black with a pale stripe down the back, but with few other distinguishing markings. Bronzed cutworms are dark brown to black on the upper side of the body and paler on the underside. The upper surface has three narrow yellow stripes and a broad white-yellow stripe running down each side. The entire body has a distinctive bronze sheen. The variegated cutworm is grey to brown with an orange lateral stripe and a series of darker lateral markings. A row of yellow or white dots runs down the middle of the back. Life histories of the various cutworms differ depending on the species. The black cutworm does not overwinter in Nebraska. Moths migrate northward from southern states in early spring and deposit clusters of 10 to 20 eggs on grasses and weeds. Wind patterns (which affect the migration and ultimate distribution of the moths) and local environmental conditions strongly influence the severity of black cutworm infestations. There may be as many as three generations per year. Bronzed cutworms overwinter as eggs which hatch in early spring. Fully-grown larvae are present by late April and pupation occurs during mid-August. Bronzed cutworms have only a single generation each year. Variegated cutworms overwinter as partially-grown larvae and resume feeding as grasses start to green up in the spring. Adults begin to appear in late spring and deposit up to 2000 eggs in clusters of 100 or more under the sheaths of grass blade. There are 2 to 4 generations of variegated cutworms each year. The armyworm, Pseudaletia unipuncta, and fall armyworm, Spodoptera frugiperda, are generally considered minor pests, but they have the potential for explosive outbreaks in turfgrass. Armyworms are 1 1/2 to 2 inches long at maturity and vary in color from gray to yellowish green tinged with pink. They have a narrow broken stripe down the center of the back and a lighter stripe along each side. The head is light brown with a distinct honeycomb pattern. Armyworm adults are light reddish brown with a small white spot near the center of each forewing. The moths fly at night and are highly attracted to lights. Fall armyworms are 1 1/2 to 2 inches long when fully grown and range in color from pink to yellow-green or gray to almost black. The fall armyworm has stripes on the body and an inverted white "Y" marking on the front of the head. Armyworms and fall armyworms do not overwinter in Nebraska and must migrate northward from southern states in the spring. Females usually begin depositing their eggs on grasses in May. Larval feeding and migration usually occur at night with larvae hiding in the thatch during the day. Infestations of these insects are sporadic and occur only when egg-laying adults successfully migrate north. Armyworms complete 2 to 3 generations in the midwest. The most serious turfgrass injury occurs in mid to late summer. The fall armyworm completes only a single generation in Nebraska. Cutworms feed at night, cutting grass blades near the soil surface. Damage initially appears as small circular dead or dying spots that increase in size to 1 to 2 inches in diameter as the worms mature. Cutworms occasionally cause severe damage on golf course greens (especially bentgrass) where they live and feed around the openings made by aerification. Armyworms also feed at night, and damage may occur before the larvae are detected. Grass blades that appear skeletonized are frequently an early sign of feeding activity by small larvae. Later, as the caterpillars mature, all above-ground plant parts are consumed. Areas that have been damaged by heavy infestations often appear closely cropped in a circular pattern. Occasionally, large numbers of armyworms will develop in one area, then migrate to another after exhausting their food supply. This has been a problem in a few instances, when armyworms moved from maturing or recently harvested wheat fields into lawns, golf courses, cemeteries, sod farms and other turf areas. Close examination of cutworm or armyworm-infested turf will reveal clipped or skeletonized grass blades mingled with green fecal pellets. Larvae will be found near the edges of damaged areas. The presence of birds, and/or animals foraging in turf areas is often an indication of cutworms and other surface-feeding insect pests. To confirm the presence of cutworms or armyworms, apply 1 tablespoon of 1% pyrethrins or 1/4 cup of lemon-scented household detergent in two gallons of water over one square yard of turf. This irritates the caterpillars and forces them to the surface where they can be identified and counted. Scratching around in the thatch with a knife also may reveal their presence. Good cultural practices may allow a healthy, vigorous turf to withstand a moderate cutworm or armyworm infestation. In most cases, the turfgrass will outgrow the injury. Generally, it takes fewer caterpillars to damage mismanaged or stressed turf. Overgrown and lodged grass in the vicinity of the turf area create an ideal environment for later cutworm or armyworm infestation. Many natural factors help reduce cutworm and armyworm populations.When the weather is warm and humid, fungal diseases sometimes infect the insects, reducing infestation levels. In addition, several parasitic flies and wasps lay their eggs on cutworm and armyworm larvae. These caterpillars are later killed by the internal feeding of the parasites. Bird predation also can result in significant reduction of cutworm and armyworm populations. When natural enemies and cultural practices are not sufficient to prevent damage and cutworms or armyworms are present, insecticidal control may be warranted. For information on insecticide applications, refer to the section on Insecticidal Control under sod webworms.