The extension office has received many calls from homeowners who are concerned about large numbers of caterpillars attacking their lawns and what they need to do to control them. The insects are armyworms and they have the ability to damage lawns quickly.
They move in large numbers marching side by side, which is how they got the name “armyworms.” Sometimes large numbers of caterpillars can be observed crossing roads and other paved surfaces. In spite of their destructive feeding, they can be brought under control and their damage minimized.
In late summer armyworms invade lawns throughout the state. The damage to established turf is primarily aesthetic but newly sodded areas are more vulnerable and can be severely harmed by their feeding. They prefer bermudagrass although they will feed on any type of grass. They consume only the leaf blades above ground and do not attack the roots.
The first sign of damage is small dead areas in the turf. Often birds can be observed clustering around the infested area. Although the birds eat the armyworms, they are unable to consume enough of them to reduce damage. To find out if armyworms are infesting your lawn, pour water mixed with some dish-washing liquid onto the grass. If the caterpillars are present they will begin to crawl up the leaf blades.
Armyworms are one-and-a-half inches in length, dark in color, and have light colored stripes down the sides of their bodies. Their head have stripes that form a “Y” shape. Adult armyworm moths are active at night and the female moths lay their eggs in the ground. They hatch in a few days, and the young caterpillars begin to feed on the leaf tissue.
The smaller caterpillars skeletonize the leaf blades whereas the larger ones consume it entirely. Armyworms are most active early in the day and late in the day. They spend the hot daylight hours down near the soil line and emerge in the late afternoon to begin feeding. The caterpillars feed on the grass blades for several days before they pupate in the soil. The adult moths emerge two weeks later. The life cycle from eggs to the adult moths averages 28 days in the warm weather of late summer.
What can be done to stop their march across your lawn? The control of armyworms is relatively simple once the problem is identified. Several insecticide products are available. Liquid insecticide applications are the most effective since they leave a residue on the foliage. Since armyworms tend to be most active in the evening and at night, make the insecticide application late in the day. One of the most common and effective treatments is the use of liquid Sevin. Other insecticide products are available such as Bayer Advanced Complete Insect Killer for Soil and Turf or Ortho Bug-B-GON MAX Insect Killer for Lawns. Both of these pesticides have containers that can be hooked to a hose for applying.
Avoid irrigating the turf within 24 hours after the application and avoid mowing for at least three days. Please make sure you follow all label directions and safety precautions when using chemical pesticides.
Armyworms are capable of causing excessive damage to lawns in a short period of time.
However, since they do not harm the roots if it is healthy, the lawn will recover in time if it is healthy. Make sure the grass is mowed at the proper height; it needs to receive adequate water and fertilizer, and keep diseases and other insect pests under control.
Timothy Daly is an Agricultural and Natural Resource Extension Agent with Gwinnett County. He can be contacted at 678-377-4010 or firstname.lastname@example.org.