Author: Dr. Phillip Roberts, Dr. Paul Guillebeau, University of Georgia
The moth has a wingspan of about 38.5 mm. The hind wings are grayish-white; the front wings are dark gray, mottled with lighter and darker splotches. Each forewing has a noticeable white spot near the extreme. Larvae are about 30 to 40 mm in length when full grown, color varies from light tan or green to nearly black. A longitudinal, pitch-colored stripe runs along each side of the body and a wider, yellowish-gray stripe runs down the back. The head of a larva is often marked with a pale, but prominent, inverted Y.
Corn, sorghum, and other plants of the grass family are preferred hosts. But fall armyworm may also attack alfalfa, beans, peanut, potato, turnip, tomato, cabbage, cucumber, cotton, tobacco, and clover.
Fall armyworms damage crops by foliage feeding and feeding on developing fruiting forms. Whorl feeding in pretassel corn can be a problem with late plantings. Larvae will also feed on developing ears. In cotton, damage occurs when larvae feed on developing bolls. Often a windowpane-like etching will form when small larvae feed on the surface of plant tissues (i.e. etching boll bracts in cotton). Fall armyworm will also feed on developing soybean pods.
This insect overwinters in Florida and along the Gulf Coast of other southern states. Moths migrate into Georgia and infestations appear in July. Eggs are laid in masses of 50 to several hundred and are covered by fuzzy scales from the female moth. Upon hatching, larvae disperse in search of a suitable feeding site. Larvae feed 2 to 3 weeks and then pupate in the soil. Several generations occur each year.
Early planting of corn is the most effective management option for fall armyworm. In cotton control of this pest with insecticides is very difficult due to the proximity of damaging populations. Coverage and penetration of the crop canopy is a must.
Fall Armyworm / Boll Worm Early Instar Species Determination
When less than 1/4 inch in length, fall armyworm and bollworm are very similar in appearance. Often scouts cannot differentiate between these two species until larvae approach 1/2 inch or greater in length. Unfortunately, larvae of this size are very difficult to control with insecticides. There are no absolute rules or keys to correctly differentiate small (< 1/4 inch) fall armyworm from bollworm larvae. However, as larvae age they become easier to correctly identify.
Suggestions for Identifying Small Fall Armyworm Larvae
- Look for etching on plant tissues where larvae are found. Small fall armyworm larvae will often feed on the surface of plant tissue such as leaves or the inside of boll bracts. The etching is similar to that of small beet armyworm feeding; but unlike beet armyworm, fall armyworm larvae disperse upon hatching.
- Head capsules on first instar fall armyworm larvae are often darker than those of bollworms.
- A black spot on the side of the first abdominal segment (just behind the last pair of true legs) is often visible. The spot is not as prominent as on yellow striped armyworms. Do not confuse with beet armyworm.
- Fall armyworm larvae often appear to be smoother or less hairy than bollworm.
- Three light parallel stripes on the first segment behind the head on the back (prothoracic shield) become visible as larvae reach 1/4 inch or greater in length.
- A prominent inverted "Y" on the front on the head is apparent when larvae reach 1/2 inch in length.