Missouri Pest Monitoring Network
Fall Armyworm I.D.

Fall Armyworm wings spread, female and male

Identification of moth
(stage attracted to and captured in traps)

Moths have light (male) to dark grayish-brown (female) mottled forewings with light and dark splotches.
They have a noticeable white spot near the extreme end of each forewing however it is more pronounced in the male.
The hind wing for both sexes is iridescent silver-white with a narrow dark border.

Identification of larvae (damaging stage)

Young larvae are initially dirty white; color may change to light tan or pinkish gray as larvae mature
Skin is smooth and free of hairs with numerous round dark spots scattered over top and sides
Head is dark brown to black
Four prolegs (3rd, 4th, 5th, 6th and 10th abdominal segments)
Maximum larvae length is one inch

Field Scouting

How to Field-Scout for Fall Armyworm:

The fall armyworm, S. frugiperda (Smith), does not overwinter in Missouri, but migrates northward from the Gulf Coast area. The first wave of migrants typically arrives in late June. Unlike true armyworm larvae, fall armyworm larvae also feed during the day and are particularly active in the early morning or late afternoon hours. This species generally requires 30 to 45 days to complete a generation.

Corn

Fall armyworm larvae feed during the day and are particularly active in the early morning or late afternoon hours, therefore, fields should be scouted during those times. Since late-planted and late-maturing corn is most attractive to fall armyworms, producers should begin scouting these fields in early June.
To determine whether your field has an economic infestation (action threshold to trigger insecticide spraying) of armyworms, randomly examine 20 plants at each of five locations per field. Take notes on the location of infestations in the field, larval size, and where the larvae are feeding on the plant.
Also, observe the presence or absence of predators and diseased or parasitized larvae. If larvae are not visible but some feeding damage is evident, carefully unroll and inspect the whorl of damaged plants for the larvae.
Control of fall armyworm larvae is recommended when 75 percent or more plants are infested and larvae are less than l.25 inches in length. Insecticide applications to control larger larvae or those within the ears are not effective. In general, it is not economical to treat for fall armyworms unless infestations are severe and plants are stressed by environmental factors. Precaution: Before you select and apply an insecticide, review the manufacturer's label for information on the proper and safe use of the material.

Cotton

When scouting fields fall armyworms, watch for egg masses by carefully examining both sides of the leaf. Fall armyworm larvae typically feed on large squares and bolls. When young larvae attack large fruit, the initial damage is etching on the inner surface of the boll bracts. This results in the characteristic "window pane" damage. They are often found in greater numbers in drought-stressed portions of the field. They also tend to occur farther down in the plant canopy and in the blooms. Fall armyworms generally spend more time feeding on individual fruiting forms than other caterpillar pests, such as cotton bollworms.
Treatment for the fall armyworm is recommended when more than four larvae per 100 blooms and bolls are present and before larvae start boring into the bolls. Insecticide applications are no longer effective once the larvae are inside the bolls. Target applications at egg masses and newly hatched larvae to obtain maximum control of fall armyworm infestations. There is no threshold for yellowstriped armyworms on cotton.

Pastures

Fall armyworm larvae tend to feed on all tender green plant tissues which give infested pastures the appearance of drought. Larvae are especially active both early and late in the day. Scouting is best accomplished during these periods to gain an accurate estimate of larval numbers.
The economic threshold for this pest in grass pastures is to treat if 3 or more larvae are present per square foot.

More Information ...

Introduction to Crop Scouting (IPM1006)
MU Extension

Management of the Armyworm Complex in Missouri Field Crops (G7115)
MU Extension

Fall Armyworm in Grass Pastures and Alfalfa
croppest article

Integrated Pest Management

University of Missouri

Missouri Pest Monitoring Network
Fall Armyworm I.D.

Identification of moth
(stage attracted to and captured in traps)

Identification of larvae (damaging stage)

Missouri Pest Monitoring NetworkFall Armyworm I.D.

Identification of moth(stage attracted to and captured in traps)

Identification of larvae (damaging stage)

Missouri Pest Monitoring Network
Fall Armyworm I.D.

Identification of moth
(stage attracted to and captured in traps)