True Armyworm

Dr. Phillip Roberts, Extension Entomologist, The University of Georgia, Department of Entomology, Tifton, GA 31793
Dr. Paul Guillebeau, Extension Entomologist, The University of Georgia, Department of Entomology, Athens, GA 30602

Description: The true armyworm moth has grayish-brown forewings, each with a white spot near the center, and grayish-white hindwings. The wingspan is about 38.5 mm. Young larvae are pale green. As larvae mature they become yellowish- or brownish-green with a tan or greenish brown head mottled with dark brown. The body is smooth and practically hairless with three, longitudinal, dark stripes: one along each side and one down the back. Fullgrown larvae may reach a length of 30 to 35 mm.

True armyworm Photo by: Randy Hudson, UGA

Hosts: Grasses and cereals are preferred but may occasionally be found on various vegetables, fruits, legumes, and weeds, especially when they are moving. Most common hosts include corn, sorghum, and small grains including wheat.

Damage: Damage is erratic from year to year. Larvae feed on succulent foliage first and then move to other parts of the plant. In headed, small grains, the caterpillars may feed on awns and tender kernels, frequently cutting through the stem just below the head. Armyworms may completely defoliate young corn. Once their food supply has been exhausted, the larvae migrate as an "army" to new host plants. Armyworm larvae feed at night.

Life Cycle: True armyworms overwinter as partly grown larvae. Early in the spring, larvae resume feeding at night, usually on grasses and small grains. First generation adults appear in May. Females deposit up to 2,000 eggs in small clusters or rows. Larvae feed three to four weeks and pupate in earthen cells 5 to 7.5 mm deep within the soil. Five or more generations are completed each year.

Control: True armyworms are usually kept below damaging populations by natural control agents. They are easily controlled with insecticides when an outbreak occurs. Treat based on defoliation thresholds. Since larvae are active at night, treatment late in the afternoon may enhance control efforts if a short residual insecticide is used.

In: Roberts, P. M. and G. K. Douce, Coordinators. 1999. Foliage Feeding Insects. A County Agent's Guide to Insects Important to Agriculture in Georgia. Univ. of GA, Col. Ag. Env. Sci., Coop. Ext. Serv., Tifton, GA USA. Winter School Top Fifty Agricultural Insect Pests and Their Damage Sessions, Rock Eagle 4-H Ctr., Jan. 20, 1999.

Selected References and Suggested Readings