Issue 14, September 8, 2014

Fall Armyworm

We have been receiving reports of large fall armyworm infestations of turf in southern Illinois. These caterpillars are stripping lawns of grass blades, then moving to and stripping adjacent lawns. They are causing damage throughout the St. Louis metro area extending east to Greenville. It is likely that other areas of southern Illinois are also being impacted. Their egg masses have been seen within the last couple of weeks in the Chicago area, so infestations could be found anywhere in the state.

Fall armyworm lawn damage.

Fall armyworm is a tropical insect, common in Mexico, Central America, and the West Indies. It is very cold sensitive, able to overwinter most years only in southern Texas and Florida in the U.S. The adults are strong fliers, migrating northward. They are common annually through much of Louisiana, Texas, and Oklahoma. The brown moths are about one inch long and are similar in size, shape, and color to many of the other moths or millers attracted to lights at night.

Fall armyworm larva.

Female moths lay clusters of eggs on grass blades and also on tree leaves, buildings, golf flags, and other structures. Egg masses contain about 400 eggs and are composed of three to four layers of eggs covered by the abdominal hairs of the female moth. If the newly hatched larvae are unable to feed where the eggs were laid, they drop down on silk threads to the turf or other plants to feed. Fall armyworm caterpillars feed on many plants. In turf, they feed on bermudagrass, Kentucky bluegrass, fescues, and ryegrass. In southern Illinois infestations, they are avoiding zoysiagrass. They are field crop pests, feeding on corn, wheat, and soybeans. They also feed on trees, shrubs, flowers, vegetables, and fruit trees.

Young caterpillars typically feed on only one side of leaves, with this window-feeding resulting in transparent tips on grass blades. Older larvae eat entire leaves. They feed throughout the day but feed heaviest in early morning and late evening. Mature larvae are one-and-three-sixteenths inch long and usually dark-colored with an indistinct light line down the back and a yellow to white stripe on each side. They can be various shades of pink, yellow, green, gray, and black, distinguished from other caterpillars by a light-colored inverted Y-marking on the head. Once the caterpillars eat all of the grass blades in one area, they will move as a group, like an army, to other turf areas to feed.

Fall armyworm larvae at turf edge.

There are usually one to two generations per year in Illinois, occurring in late summer to early fall. Numerous generations occur farther south with four in Oklahoma and Louisiana and nine to eleven generations per year in the southern tip of Texas. Populations build in the south before moths migrate north into Illinois.

Damage to turf is to the leaf blades, which will be completely eaten. Treating the caterpillars and irrigating typically results in the crowns sprouting new leaves, restoring the lawn. Fall armyworm larvae are controlled by the same insecticides used to control sod webworm including bifenthrin (Onyx, Talstar), carbaryl (Sevin), chlorantroniliprole (Acelepryn), clothianidin (Arena, Aloft), deltamethrin (Delta Gard), indoxacarb (Provaunt), lambda-cyhalothrin (Scimitar), spinosad (Conserve), and trichlorfon (Dylox). The insecticidal nematode Steinernema carpocapsae is also effective. (Phil Nixon, Ed Nangle, Mark Black)

Phil Nixon

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