Damage from armyworms in turf in northwestern and southwestern Illinois has been reported. Although common in turf, armyworms rarely become numerous enough to be much of a problem. However, when they are numerous, they can eat off every blade of grass in several thousand square feet of turf per night. In the evening you have nice, green turf, and in the morning all you have are crowns and thatch.
True armyworm caterpillars grow to about 1-1/2 inch long. Mature larvae are brown to black with five orange stripes, one down the back and two on each side. Small caterpillars are dark in color with less noticeable stripes. Caterpillars hide in the thatch during the day and come out to feed at night.
Armyworms spend the winter in the southern United States, and the moths fly north in the spring. Armyworm moths are about 1 inch long with tan to grayish-brown wings. Each front wing has a single white dot near the center. The female moth lays her white eggs in rows or groups on grass blades and rolls the grass blade around them. There are usually two generations per year in Illinois. Moths are very numerous in Illinois in the fall, being one of the last moths seen around lights at night as winter approaches.
In the spring, caterpillars may become numerous in wheat and then move from those fields into nearby turf areas as the wheat matures and turns brown. This is the most common damage scenario in turf, with the damage being in housing areas and golf courses next to farming operations.
The second generation occurs in late summer and is the one damaging turf at this time. Typically, this generation is attacked heavily by tachinid flies. White eggs, usually laid on the back just behind the cater pillarís head, hatch into legless maggots that tunnel into and eat out the caterpillarís insides. When fully grown, the maggots leave the caterpillar carcass to pupate and emerge as adult flies similar in appearance to house flies. Usually at this time of year, it is difficult to find caterpillars without several tachinid eggs on their backs. The rate of parasitism must be low in western Illinois for this insect to be numerous enough to cause damage. Armyworm is also attacked by a disease that causes the caterpillars to die while clutching a grass blade or stem.
As mentioned before, the caterpillars feed at night. Typically they move in large numbers like an army across turf, eating all of the green grass blades. Fre-quently, they will eat half of a home lawn in one night, eating the rest of it the next night. Because only the blades are eaten, irrigation helps the grass crowns grow new grass blades quickly.
Scout with a disclosing solution. Mix a teaspoon of 5% pyrethrin insecticide or a tablespoon of dish-washing soap in a gallon of water. Distribute this evenly with a watering can or other method over a square foot of turf. Any armyworms or other caterpillars present should come to the surface within a minute or two. Two to three or more caterpillars per square foot are enough to cause damage.
Control can be accomplished with a treatment of bifenthrin (Talstar), carbaryl (Sevin), chlorpyrifos (Dursban), diazinon, halofenozide (Mach 2, Grubex), spinosad (Conserve), trichlorfon (Dylox, Proxol), or other labeled insecticide. Insecticidal nematodes, either Steinernema carpocapsae (BioSafe) or Heterorhabditis bacteriophora (Cruiser), should also be effective.