Male moths have dark gray front wings mottled with darker and lighter splotches. There is a prominent pale, diagonal marking near the center of the front half of each wing and a prominent white spot at the extreme tip. The front wings of female moths are dull gray brown with only small, inconspicuous markings. The hindwings of both sexes are white with a slight purplish sheen. The wingspan is about 1 1/2 inches. Eggs are pale gray, laid in masses, and covered with grayish, fuzzy scales from the body of the female moth. Mature larvae may be green, brown, or almost black and measure about 1 1/2 inches long. There are black and reddish brown stripes on each side of the body and four small, black spots on top of each abdominal segment. The head capsule is mostly black and is marked with a pale, inverted “Y” on the front.
Fall armyworm does not overwinter in Oklahoma. It reinfests the state each year by moths that migrate northward from the Gulf Coast, Texas, or Mexico. Migrating populations usually reach Arkansas and Oklahoma by late June. Each female lays about 1,000 eggs in masses of fifty to several hundred. Larvae are present by early July. After feeding for two to three weeks, larvae dig into the soil to pupate. A new generation of moths emerges about two weeks later. There are several overlapping generations extending into October or even November in some years.
This species will feed on a very wide variety of plants but prefers grasses. Most turfgrasses are subject to infestation.
Fall armyworms are potential turf pests in late summer and fall. Large numbers can consume all above-ground plant parts, and they are capable of killing or severely retarding the growth of grasses. This species may migrate in large numbers in search of new areas in which to feed. Moths are attracted to lights and may lay masses of eggs on non-host plants, walls, clothes on lines, etc.
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. Treatment may be needed when 5 to 10 larvae are found per square yard of turf.