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Controlling Armyworms

Early scouting and proper timing of insecticide application are keys to controlling the armyworms that have infested pastures throughout much of the state in recent weeks.

“They’re all across Arkansas, and they’re a big problem,” Stone County Extension Agent Tyler Caston said.

Though they are called “worms,” these pests are actually a caterpillar, the larva of a moth. There are two types that trouble Arkansas farmers and homeowners, according to a fact sheet from the UA Extension Service:

“In Arkansas, the “true” armyworm (Pseudaletia unipuncta) is more of a spring pest of cool-season grasses and tall fescue. The fall armyworm (Spodoptera frugiperda) is a summer/fall pest primarily of bermuda grass, but it can also damage fall-seeded, newly established winter annuals, fescue and orchardgrass.”

Armyworms are not just a problem for farmers but also for lawns and gardens, and Caston said he has received several calls about them. “They’ll be in lawns, pastures, and hayfields,” he said.

Although the damage they cause – brown or burned-looking patches that resemble drought damage – often seems to appear overnight, it actually takes place over a period of weeks. For this reason, scouting for them ahead of time is recommended to head off serious damage.

“With armyworms, if they don’t know they have them already, they need to be out scouting,” Caston said.

Birds are an ally for farmers in controlling armyworms as they are natural predators for the caterpillars. They can also alert people to infested areas, as they may be seen gathering in spots with high concentrations of armyworms.

When scouting, it is recommended to first check for armyworm larvae in and around areas with dead grass or where birds are feeding. Decisions about when to spray should be based on the number and size of caterpillars found in the field. The Extension Service recommends sampling areas of 1 square foot, at several different locations across a field. A sampling device may be constructed of small PVC pipe that covers 1 square foot. Drop the square in random locations and then search for worms within that square.

“If you can count three in several spots around your field, you need to be spraying,” Caston said.

See more in the Aug. 31, 2016 issue of the Leader.

8-31 fall armyworm

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