Examine your lawn before each mowing to detect problem areas. At the same time, look for weeds. A dense stand of healthy grass prevents most weeds from growing, so abundant weed growth indicates that the lawn is unhealthy and susceptible to other pests.
Newly planted turfgrass is especially vulnerable to problems and has different irrigation and fertilizer requirements than established turfgrass. An indication that a lawn may be infested with insects is when the adults (e.g., moth or beetle stage) of pests are drawn to lights at night or when vertebrate predators (birds, raccoons, or skunks) are digging in your lawn for caterpillars and grubs.
Insects coming to the light, however, may be drawn from far away and specific animal activity on the lawn is not a foolproof indicator. They may be feeding on earthworms instead of insects. Another indicator is if you see small moths flying up from the grass when you mow.
If you observe damage, determine the actual cause. If you suspect damage is insect related, look for the pest. The most accurate way to do this is by using either the drench test or by inspecting roots.
Drench Test. To detect chinch bugs, adult billbugs, and caterpillars including armyworms, cutworms, and larvae of lawn moths (sod webworms), perform a drench test by mixing 1 to 2 fluid ounces (2-4 tablespoons) of dishwashing liquid (such as Lemon Joy) to a gallon of water. If you are using a concentrate (i.e., Ultra) version of a dishwashing liquid, 1-1/2 tablespoons per gallon of water is adequate. Two gallons may be required where soils are dry.
Apply the solution to 1 square yard of lawn as evenly as possible using a sprinkling can. Test an area that includes both relatively healthy grass and adjoining unhealthy grass. The drench will cause insects to move to the surface. During the next 10 minutes, identify and count the number of pest insects.
The drench test is effective for detecting chinch bugs and caterpillars including armyworms, cutworms, and sod webworms, but it does not detect grubs.
Locating and correctly identifying a pest is important because different pests require different treatments, timing, and application methods.
After identifying the insects, count the number of each type of insect found. Some of the insects you find may be beneficial or at the least, non damaging.
The mere presence of an insect pest does not imply it is the cause of unhealthy lawns or that an insecticide is needed. You will most likely find a few pest insects in any healthy lawn. Treatments are not recommended unless the population level of the insect pest reaches a predetermined level called a threshold.
Thresholds are the population levels at which the number of insects feeding exceeds the ability of a healthy lawn to withstand the damage they cause. For example, an insecticide usually is not needed unless more than about 5 armyworms and cutworms or 15 lawn moth larvae per square yard. Sample several different areas of the lawn to better estimate populations overall, especially if numbers are close to suggested thresholds.