E-57
DEPARTMENT Of ENTOMOLOGY
field crops insects
CONTROLLING ARMYWORMS
C. Richard Edwards and David L. Matthew Jr., Extension Entomologists
Armyworms feed on the leaves and stems of small grains, grass and alfalfa, may eat the beards of wheat heads and even clip off wheat, rye, oats and barley heads. They feed on the whorl leaves of young corn and sorghum plants.
Infestations of true armyworm, fall armyworm and yellow-striped armyworm are found in Indiana every year; however, only the true armyworm and fall armyworm cause noted economic loss. The severity of destructive populations depends upon moth migration patterns, weather favorable to moth and larval development, and the presence of their parasites, predators and diseases. Infestations causing economic damage and requiring control develop once every 4 or 5 years.
LIFE CYCLE AND DAMAGE
The true armyworm moth is about 1 inch long, tan in color and has a tiny white dot in the center of each forewing. The moth is attracted to lights and is found at night around windows and doors.
The moth lays eggs in rows or clusters on the lower leaves of grass plants. The larvae are greenish in color and move about with a looping or "measuring worm" motion. In 3 or 4 weeks they are full-grown hairless caterpillars, about 1-1/2 inches long, smooth-
skinned and dull-colored with greenish and dark stripes running the length of the body. This first or spring generation of armyworm causes damage generally beginning about the time wheat heads emerge above the flag leaf. Later generations are generally held in check by natural enemies.
Armyworm is most active at night and during cloudy days. Larvae hide beneath crop debris at other times. Infestations usually develop in grass pastures, fence rows and roadsides where vegetation is dense, in areas in small grain fields where the crop has lodged or matted against the ground, and on grasses not controlled in corn fields. Once the worms have consumed the available food, they "march" in great numbers to find other plants to feed upon. This is why they are called armyworms.
Armyworms may migrate into corn fields, but not always. Sometimes the moths lay their eggs in grass or grain fields that are later planted to corn. Therefore, the true armyworm may be already present to attack the corn seedlings as they come through the ground. This is particularly true for another species, the fall armyworm, which may feed on late-planted corn and sorghum.
The fall armyworm does not overwinter in Indiana nor the midwestern states. Moths migrate in from southern states. Damage is similar to that of corn earworm as it feeds on the whorl of both corn and sorghum. Feeding may also occur on seedling small grain and alfalfa plants during September and October. Unlike the true armyworm, fall armyworm may be found actively feeding during the daylight hours.
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA 47307