Cutworm adults are medium-sized moths with a wingspan of 1 to 2 inches. Most species are brownish or grayish with various darker or lighter markings on the front wings. Larvae are black, gray, or brown caterpillars that are about 1 1/2 inches long at maturity. Some species have darker or lighter spots or stripes on the body. At least eight species are known to damage turf in Oklahoma. The black cutworm (Agrotis ipsilon) is the most commonly reported and the bronzed cutworm (Nephelodes minians), variegated cutworm (Peridroma saucia), and bristly cutworm Lacinipolia renigera) occasionally cause problems in turf. The granulate cutworm (Agrotis subterranea), army cutworm (Euxoa auxiliaris), dusky cutworm (Agrotis venerabilis), and claybacked cutworm (Agrotis gladiaria) may damage turf in years when they are abundant.
Cutworms overwinter as eggs, larvae, or pupae, depending on the species, and damage to turf can occur from late February to early October. Army cutworms overwinter as larvae, feed in early spring, and have one generation per year. Damage in February and March is most likely to be caused by this species. Claybacked and dusky cutworms also overwinter as larvae and have one generation per year, but larvae develop later in spring. They and the bristly cutworm are most likely to cause damage in April and May. Bronzed cutworms overwinter as eggs and have one generation per year. Damage is most likely in May. Variegated and black cutworms overwinter as pupae and have several generations per year. Variegated cutworm damage is most likely in May while black cutworm damage is usually reported in late summer or fall (August and September). Local populations of some species are augmented by migration of moths. Black cutworms migrate north in spring and army cutworms migrate from the mountains of Colorado in fall.
In years when cutworms are heavy, surrounding areas (e.g., shrubs, garages, out-buildings, etc.) may be used as hiding places for large numbers of adult moths (“millers”). Larvae pupate and the emerging moths often congregate before laying eggs or migrating. Those that remain in the area will eventually die.
Cutworms are general feeders and attack a wide range of plants. All common turfgrasses are susceptible to damage.
Larvae feed at night on the leaves and crown and may cut off plants near the soil line. During the day, they are found hiding in holes, under debris, or under thatch near the surface of the soil.
Inspection & Control
An infestation in turf can be detected by applying irritants such as dish detergent. Add one-quarter cup of dry or one ounce of liquid detergent to one gallon of water in a sprinkling can and apply the solution to one square yard of turfgrass where an infestation is suspected. Also effective is mixing one tablespoon of a commercial garden insecticide containing 1 percent to 2 percent pyrethrin in one gallon of water. If the thatch is dry, irrigation before the test is advisable. The caterpillars will surface within 10 minutes of soaking and can be found by separating the blades of grass. Turf should be treated if 5 or more cutworms are found per square yard.