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Armyworms Making Fall Advance

Fall armyworms reach about 1½ inches long at maturity, with their body color varying on their stage of development and diet.

Lawns, pastures and even winter food plots are at risk as an insect army advances across much of the state in higher than normal numbers. Blake Layton, entomologist with the Mississippi State University Extension Service, says fall armyworms are the most damaging insect pests of bermudagrass hayfields and pastures. Armyworms attack golf courses and lawns, and they can defoliate an entire yard or field almost overnight. "They are called fall armyworms because their numbers are highest in late summer and fall, and hay producers, cattlemen, turf managers and homeowners should expect to be dealing with this pest until frost,” Layton said. Armyworms arrive each summer when moths migrate back into the state from the Caribbean, Mexico and areas of South America. “Severity and distribution of fall armyworm infestations depend on when moths arrive, how many moths arrive, where in the state they arrive and weather conditions they experience once they get here,” Layton explains..

Fall armyworms are caterpillars that reach about 1½ inches long at maturity. Their body color varies depending on their stage of development and diet. Most are green or tan, but some can be dark brown to almost black, especially late in the year. The body is punctuated with dark spots. When they metamorphose into moths, they are about ¾-inch long when resting with their wings folded. They are active at night and spend the day resting in foliage.

Eggs hatch in two to five days, and the newly emerged larvae begin feeding on the underside of leaf blades. Their feeding habits result in tiny, white “windowpanes” in the leaf blades or a white frizzing of the leaf tips .Damage caused by young caterpillars is easy to overlook because fall armyworms do 80% to 90% of their feeding in the last two to three days of their life.

There are treatment options for lawns, pastures, fields and golf courses, but the key is vigilance and quick action when the pest is detected.

Well-established home lawns that are heavily damaged by fall armyworms will grow back, but homeowners can speed along the process with good watering, fertilizer and weed control. Both pyrethroids and non-pyrethroid products are available for lawns. Hose-end applicators work for small areas, while broadcast sprays work for large lawns.

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