Insect pests sometimes feed on lawns, though not as often as is commonly believed. The damage insects cause often produces symptoms - usually small dead spots - which are similar to those produced by more common problems such as diseases or overwatering. Just because you see insects flying out of your lawn does not mean those insects are causing the damage! Before you apply insecticides, it's a good practice to make sure that insects are causing the damage.

You can check for a variety of turfgrass pests by mixing one tablespoon of a commercial garden insecticide containing 1 to 2 percent pyrethrins in 1 gallon of water. If the insecticide contains only 0.5 percent pyrethrins, use 2 tablespoons. Or, you can substitute one to two fluid ounces of a liquid dishwashing soap for the pyrethrins. Apply the solution to one square yard of turfgrass as evenly as possible using a sprinkling can. This will bring cutworms, sod webworms, and other caterpillar larvae to the surface within ten minutes. It is normal to find a few caterpillars. An insecticide is usually not needed unless there are more than 5 cutworms or 15 lawn moth larvae per square yard of lawn.

Cutworm larvae are dark-colored, and can grow up to 2 inches long; they typically curl up and lie still when disturbed. Lawn moth larvae are creamy-colored and smaller, and have a distinctive double row of brown or black spots down their backs. Heavily-infested turfgrass appears moth eaten, with irregular patches of brown grass or bare areas.

A number of insecticides may be used to control cutworms and sod webworms, including Diazinon, Dursban and B.t., a biological control. If you want to use B.t., apply it while the larvae are still quite small. Large larvae are not easily killed by B.t.

Neither the pyrethrum nor the soap solutions will help you detect white grubs, which are the larvae of beetles. Look for white grubs by carefully digging around the roots of the grass. The grubs are C-shaped, white, and up to 1 inch in length. When these insects are numerous, the roots of the grass are often eaten away and you can roll the turf back like a carpet. If you find more than six per square foot, consider applying an insecticide. Except for B.t., most of the sprays used for cutworms and webworms would also control white grubs.

Cultural controls are the oldest and most widely used approaches to insect control. Good turfgrass management not only produces a more healthy turf which can tolerate more pests, but also reduces the chances of insect attacks. Cultural controls include sanitation, (removing the material which can harbor insects), irrigation, fertilization, aerification and mowing practices.

Thatch, the buildup of a thick layer of organic material on the soil surface, can increase the damage caused by insect pests. It provides a place for insects to hide, and also inhibits insecticidal control. Insecticides cannot penetrate the heavy organic matter to reach the crowns or soil where the pests are hiding. A heavy thatch layer also prevents water, fertilizer and air from reaching the soil, so the grass is weakened and more susceptible to insect damage.

You will be able to detect insect pest injury much sooner in a poorly maintained lawn. Also, weak lawns recover slowly, while vigorous grass can outgrow the effects of insect pest infestations. Lawns under water stress stand a greater chance of being damaged by chemicals applied for pest control than do well-watered lawns. Mowing lawn at the proper height helps keep grass healthy and better able to outgrow insect injury.