Time to watch out for armyworms

By: By Eileen Coite - Contributing Columinst

By Eileen Coite

Contributing Columinst


Around this time each year the fall armyworm shows itself in some areas. Whether they will appear at your farm or lawn remains to be seen, but we should all be on the lookout. Armyworms can devastate a hay crop in a very short period of time. The following information and tips may help you fight this army of insects before they take over.

What Are Fall Armyworms?

Fall Armyworms are larvae (caterpillars) that are green, brown, or black larva as long as 1.5 inches and have a dark head capsule usually marked with a pale but distinct, inverted “Y”. They have a black longitudinal stripe down each side of their body and a yellowish-gray stripe down their back. The adult fall armyworm is an ash-gray moth having front wings that are mottled with white or light gray spots near the tips. The back wings are white with a narrow, smoky-brown edge. Moths become active at twilight and feed on nectar. They have an average life span of 2 to 3 weeks. Female moths lay eggs at night in masses of up to several hundred that hatch within 2 to 4 days. Development from egg to fully grown larva (caterpillar) requires about 2 to 3 weeks. At this point larvae burrow down into the soil and form pupae. The moths emerge in about 10 to 14 days.

What Damage Can Fall Armyworms Cause?

While this article concentrates on pastures and hay fields, please be aware that fall armyworms will attack all types of turfgrass including lawns and other crops such as small grains, beans, peanuts, potatoes, soybeans, sweet potatoes, turnips, spinach, tomatoes, cabbage, cucumbers, cotton, tobacco, and clover stands. They feed any time of the day or night, but are most active early in the morning or late in the evening, so these are the best times to scout your fields. When abundant, these caterpillars eat all available plant tissue and crawl in “armies” to adjoining fields. They tend to start from the edge of a field. Damage varies and grass may appear to be thinned out in some situations or may have a dead brown frosted appearance. The presence of 3-5 medium to large fall armyworms per square foot justifies initiation of control measures. Armyworms can wipe out an entire field almost over night. To date this year, I have not heard of armyworm infestation, but the summer is not over!

How do I Control Armyworms in Hay Fields and Pastures?

Our ability to effectively manage fall armyworms relies heavily upon two things. The first is an early warning that fall armyworms are present and beginning to show up in our part of the state. The second important bit of information is an understanding of the biology of this pest as has been mentioned above. We should begin scouting fields during mid to late June and continue throughout the summer. An easily detectible sign of armyworms is the presence of flocks of birds (especially cattle egrets) feeding in pastures or hayfields. Even if birds are not observed, check fields every few days or as often as daily this time of year.

Hay and livestock producers should be aware that since animals consume the forage that is sprayed in an armyworm attack, only chemicals labeled for the use on pastures and hay fields should be applied. If a chemical is recommended to you, be sure to double check the label for this reason. Contact the extension center for more guidance on prevention and control of armyworms if they are spotted.

Eileen Coite is the County Extension Director for the Sampson County Cooperative Extension Center.

Eileen Coite is the County Extension Director for the Sampson County Cooperative Extension Center.