Department of Entomology
Entomological Notes

Spodoptera frugiperda (Smith)

The fall armyworm is a warm weather species that migrates into Pennsylvania. In most years this pest is rarely seen on field corn in the Commonwealth, but when it appears in high numbers it creates considerable concern, as it did in 1982.

The fall armyworm is a frequent pest on sweet corn and other vegetable crops in the southeastern areas but is of only minor importance on field corn. Fall armyworm infestation of field corn occurs irregularly in Pennsylvania. Over the past 20 years, infestations have approached moderate levels only several times and in those years, corn yield losses were negligible.

© Marlin Rice Iowa State University

Description

The adults are similar in size and shape to other moths in the cutworm family. They are grayish to buff in color with a wing spread of 1-1/2 inches. The front wings of the male are dark gray with mottled splotches and a small whitish area near the wing tips. The front wings of the female are the same color but the markings are less distinct, the moths are seldom seen because they hide during the day and are active at night.

The dome-shaped, sculptured eggs are laid on grass blades and plant leaves in clusters of 50 or more. The eggs are dirty white to gray in color and are moderately covered with grayish buff hairs, which the females rub from their bodies.

Newly hatched larvae have black heads and are white to pale green. For the first few days the young larvae feed near the surface of the ground. After about a week they move up onto the plants and consume all leaf tissue except the veins and midrib. In cornfields larvae can be found hiding in the whorl during the day.

Fully grown larvae are 11/4 to 11/2 inches in length and vary in color from pale green to almost black. They closely resemble true armyworm larvae in appearance. The heads of fall armyworms have a prominent inverted "Y"; black tubercles from which hairs arise are arrayed on the body. The pupae are found an inch or so in the soil. Their smooth, leathery skin is reddish brown to dark brown.

Life History

Fall armyworms overwinter along the Gulf Coast and moths migrate into Pennsylvania. Their arrival varies with the year, but this usually occurs between late July to mid-August. Their late summer activity is the reason for the name, fall armyworm.

Upon arrival, the moths deposit masses of eggs on green plants. The eggs hatch in about 5 to 7 days. The small larvae feed on plants near the ground or in protected areas such as in the whorl of corn plants. They usually go unnoticed until they are approximately an inch long. The larval period lasts about 15 to 18 days. Mature larvae burrow an inch or so into the soil to pupate. The pupal stage lasts nearly 2 weeks and then a new generation of moths emerges. Some eggs are deposited in the same general area, but many moths move forward to infest new areas. Fall armyworm activity stops when freezing temperatures approach.

Damage

Fall armyworm injury to corn plant. Dennis Calvin collection.

Fall armyworm damage to field corn may occur from late July until mid-August and is almost always confined to late planted fields not yet in tassel. Evidence of their presence is ragged feeding of the whorl leaves with wet, brown, sawdust-like pellets scattered throughout the whorl. When larvae are numerous, all leaf tissue except the midrib may be consumed. Since fall armyworm larvae are leaf feeders and arrive fairly late in the season, their damage to the crop is seldom serious. Unless the growing point is destroyed, damaged plants will recover without any noticeable yield loss.

Repeated attack on the same field by a succeeding generation is very rare. The damage for the season is generally over in a week or so after the first feeding.

Fall armyworm larva damage on corn foliage. Dennis Calvin collection.

Control

Fall armyworm larvae are difficult to control. Corn plants often are too tall to spray with conventional ground rigs. A large volume of water is needed (about 100 gallons per acre) to obtain satisfactory control. Many insecticides are ineffective against fall armyworm larvae.

Because of small yield losses resulting from fall armyworm infestation and the difficulties experienced with control efforts, it is questionable if control measures should be attempted. Control should be undertaken only when 100 percent of the plants are infested and they are less than 30 inches high.

If a control measure is warranted, check the current issue of the Penn State Agronomy Guide for recommended insecticides and dosage rates. You also may check with your county agricultural Extension agent or farm supply dealer for suggested control measures.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

Authored by: Stanley Gesell, Extension Entomologist, 1983 Dennis Calvin, Professor

Last updated: 4/20/2000

DISCLAIMER

This publication is available in alternative media on request.

Where trade names are used, no discrimination is intended and no endorsement by The Pennsylvania State University or Pennsylvania Department of Agriculture is implied.

Entomological Notes are intended to serve as a quick reference guide and should not be used as a substitute for product label information. Although every attempt is made to produce Entomological Notes that are complete, timely, and accurate, the pesticide user bears the responsibility of consulting the pesticide label and adhering to those directions.

Issued in furtherance of Cooperative Extension Works, Acts of Congress May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture and the Pennsylvania Legislature. D. Jackson, Director of Cooperative Extension, The Pennsylvania State University.

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