For example, treatment for Japanese beetle grubs isn't justified unless there are more than 10 grubs per square foot. Unless someone peels back the sod at several locations and checks to see how many larvae are feeding on grass roots, you won't know if the pesticide is needed.
By spring, grubs are usually too mature to be controlled by pesticides. Scout for grubs in late summer and early fall to determine if treatment is necessary while next year's grubs are still small enough to control. (If treatment is justified, August is usually the best time.) Because grubs feed below-ground, insecticides need to be watered in before they dry on grass leaves to be effective.
Similarly, scout for surface feeders (such as cutworms, sod webworms, chinch bugs, and bluegrass billbugs) before treating.
Regardless of the pest, the best way to minimize damage is through prevention:
Keep turf healthy through proper mowing, watering, and fertilizing. Healthy turf will tolerate more pests.
Plant the right grass for your location. Choose grasses that resist pests, such as endophytic varieties of perennial ryegrass and fine leaf and tall fescues. (Endophytes are beneficial fungi that live on the grass and discourage surface feeders.)
Scout before you treat. If you use pesticides, treat when the pest is most vulnerable, and follow all directions carefully. To prevent water pollution, never apply pesticides when ground is frozen or saturated. To prevent drift and volatilization (which releases pesticides into the air), do not apply when temperatures are high or it is windy.