The fall armyworm is a tropical insect that overwinters only in the warmest areas of the United States.
As populations build throughout the summer, they move northward on weather fronts, often arriving in Oklahoma in late summer. Because several generations develop during the summer, the generations overlap and effectively create a continuous supply of moths (and eggs). Any fall planted wheat field, pasture and yes, even established lawns can become targets of this feeding insect.
Fall armyworm infestations often go unnoticed for a while because they don’t cause obvious damage until they get bigger. To indicate the stage of growth that a caterpillar is in, we refer to them as instars. The first instar is the caterpillar just after it hatches. A second instar is the caterpillar after it has shed its skin for the first time. The caterpillar will normally shed its skin five times before it quits feeding. A sixth instar has shed its skin five times and will feed, bury itself in the soil and pupate. If you were to ration out a supply of food to feed each instar, you would need to reserve 70% of the total supply just to feed a sixth instar caterpillar. It is similar to trying to feed a hungry teenager. Like a teenager, a sixth instar armyworm can eat lots of food in a relatively short time.
Army worms are best controlled before they reach the sixth instar. The key is to recognize signs of feeding done by the smaller instars. During the first three instars, the caterpillar does not remove much plant tissue. It will scrape off the epidermis of the leaf, leaving a clear, papery membrane that you can see through. This type of feeding is called “windowpaning”. When “windowpaning” is detected, control measures need to begin.
Several insecticides are registered for control of fall armyworms:
In Wheat fields: Lorsban SG, Warrior T, and Parathion(methyl or ethyl)
In Pastures: Sevin, Malathion, Confirm 2F, Lambda-Cyhalothrin
In home Lawns: Bacillus thuringiensis (Javelin), Sevin or Orthene, Bayer Advanced Lawn and Garden Multi-insect Killer
Remember to follow all label directions before applying any pesticide.