Symptoms of Armyworm
On Lawns - Armyworms cause problems in lawns. Their work on your lawn shows up as round, bare areas. In large numbers, they will eat the grass right down to the soil. They sometimes travel in large groups, and usually feed at night. The damage they do resembles that caused by sod webworms. If you lift up the dead sod in these areas, you'll find armyworms in the soil.
In Flower and Vegetable Beds -- After chewing away at grass, armyworms move on to many ornamental plants where they will eat leaves, stems, and buds. They like corn, beans, cabbage, tomato, and other vegetables.
Checking For Armyworm
To determine if you have a large enough armyworm population to require attention mark off two sections of lawn measuring 2 feet by 2 feet in the early summer. Choose one damaged area and one undamaged area. Then mix 2 tablespoons household liquid detergent into 1 gallon water, and using a sprinkling can, pour it evenly over each area. Thick thatch areas may require several gallons of soapy water for good saturation. The soap will irritate any armyworms in the turf, causing them to crawl to the surface in 5 to 10 minutes. If no armyworms appear, lawn damage is probably due to disease or some other insect.
How Many To Worry About? - Only two or three worms per square foot of healthy lawn does not represent a serious problem. More than three per square foot requires some control steps. An infestation of even one larva per square foot of lawn already stressed from compacted soil, lack of water, or lack of food, will require treatment.