Be watchful for black cutworm activity on golf greens and other fine turf areas. Based on moth trapping by corn growers and other agriculturists, large numbers of black cutworm moths are migrating from the South into the state. Heavy numbers are being found in southern Illinois, with pockets of high numbers in central Illinois. Much lower numbers have already arrived in northern Illinois.
Black cutworm feeds heavily on bentgrass, tall fescue, and perennial ryegrass, being unable to develop well on Kentucky bluegrass. As a result of host preference and height-of-cut, black cutworms are usually not a problem in home lawns, parks, and similar turf areas. On golf greens, larvae live in the greens or crawl onto them at night, eating the grass blades off in a circular area 1-1/2 to 3 inches across. These areas look similar to ball marks and are not noticed as insect damage by golfers. Insectivorous birds such as starlings, cowbirds, and robins search out the caterpillars during the day. In pulling them from the ground, the birds tear out small divots of soil that are unsightly and cause putts to stray off target. Similar damage occurs on bentgrass fairways but is less noticeable due to the higher height of-cut.
Watch for insectivorous birds feeding on greens and then confirm cutworm presence with a disclosing solution: a mixture of a teaspoon of 5% pyrethrum or a tablespoon of dishwashing detergent per one gallon of water. This mixture is spread evenly over a square foot of turf. Within 30 to 60 seconds, any caterpillars come out onto the turf surface. Black cutworm larvae are heavy bodied and darkish, with indistinct stripes. Mature larvae are 2 inches long.
Various insecticides are effective controls, including bifenthrin (Talstar), carbaryl (Sevin), deltamethrin (DeltaGard), halofenozide (Mach 2), spinosad (Conserve), and trichlorfon (Dylox), as well as insecticidal nematodes. Black cutworm has multiple generations per year from this time of year into late fall, requiring frequent scouting.