Fall Armyworms

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With fall armyworms numbers on the rise in North Carolina, we need to discuss characteristics, scouting and control strategies. Fall armyworms have multiple generations each year and are known to have a broad range of hosts. Populations maybe found in lawns, turf, field crops, and pastures. Fall armyworm larvae live for about two weeks, but this can be dependent on temperature. In the first ten days, larvae do not eat very much and are easier to control than the larger life stages. The large caterpillars cause almost all of the damage. There are two distinct features that identify fall armyworms. Their head has light markings that form an upside down “Y” and their other end has four black dots that form a square.

Alabama Cooperative Extension

Fall Armyworm Caterpillar- Notice the “Y” on the head and four dots forming a square on the rear.

The only way to determine if and how many fall armyworms are present is to scout. When inspecting lawns or turf, kneel and looking at the top of the grass blades during cooler parts of the day and down near the soil surface during the hotter parts of the day. For row crops and forages, a sweep net is an easy method to sample for armyworms. A sweep net will pick up larvae that is too small to find. Use sweep nets in the early morning or late afternoon. Count how many fall armyworm caterpillars you find per square foot. If you find more than two or three caterpillars per square foot, it is likely time to apply an insecticide or cut the field for hay. While scouting, the size and number of armyworms should be noted. This will determine a proper control strategy.

The decision to treat for fall armyworms depends on the stage of life of the population. Timing is important. If infestations are detected too late, the damage may already have been done. Caterpillars that are less than half an inch long are easier to control and cause less feeding damage. Caterpillars more than half an inch long are difficult to kill and are responsible for most of the damage. If the population is a majority of one size, control decisions are easier to make. If most of the caterpillars are large (1 to 1.5 inches), then it is likely too late to control the population. If the population is mostly small caterpillars (0.25 to 0.5 inches), they may not require as extreme measures in order to manage them.

If a hayfield is close to harvest, go ahead and harvest early. Frequently, mowing is the best option for salvaging a hay crop and it may be possible to avoid using an insecticide. In pasture settings, cattle can be used to intensively graze the forage before the caterpillars consume it all. In turf, mowing may mechanically kill a few caterpillars but will not provide adequate control.

Products for home lawns will usually be labeled for caterpillar pests rather than specifically for fall armyworms. There are multiple control options for armyworms in pastures. They range in price, residual, and level of rain-fastness. For more information about fall armyworms or control contact your local N.C. Cooperative Extension office.

Fall Armyworm Control Options in Forage Crops

Written By

Kinsey Everhart, N.C. Cooperative ExtensionKinsey EverhartExtension Agent, Agriculture - Livestock and Row Crops Call Kinsey Email Kinsey N.C. Cooperative Extension, Anson County Center
Updated on Aug 12, 2021
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