What Insects Kill Grass?

Dying, discolored lawn grasses or quickly growing bald patches often indicate the presence of an insect pest. Several different types of insects can cause widespread damage to the lawn, especially during the active spring and summer season. Identifying the culprit and quickly working to eradicate the insects can save your grass and help prevent future problems. Pesticides aren't always necessary, but when they are wear eye protection, a face mask, gloves and long sleeves to prevent contact with the chemicals.

The Root of the Problem

Insects feeding on the roots of your grass typically cause the greatest lawn damage. White grubs and billbugs, both members of the Coleoptera family, can completely destroy the grass in their feeding area. Grubs resemble worms with six legs near the head, while billbug larvae resembles a worm and the adult pest is beetle-like with a long snout. White grubs and billbugs are usually a late spring or early summer problem. Other white grubs include June bugs (Phyllophaga), which also feed most in early summer, and Japanese beetles (Popillia japonica), which are typically a problem in mid- to late-summer. Avoiding drought stress by irrigating regularly so the lawn receives 1 to 3 inches of water weekly greatly reduces root feeder damage. Apply a granular grub pesticide, such as one containing Imidacloprid, with a fertilizer spreader at the rate of 2.87 pounds per 1,000 square feet of lawn, or at the package recommended rate. For most root pests, make the applications once yearly in late spring, except for Japanese beetles, which require a late-summer application. Water after application and stay off the lawn until the granules dissolve.

No Leaf Unturned

Leaf feeders include chinch bugs (Blissus leucopterus) and greenbugs (Homoptera). Chinch bugs measure 1/5 inch long and have white-and-black bodies. Greenbugs, a type of aphid, measure 1/8 inch and have green or black bodies. Both insect pests feed on the sap in the grass foliage, leaving behind yellow or orange discoloration that eventually causes the lawn to brown and die. Damage can occur at any time from spring through late summer. Proper watering and avoiding over-application of nitrogen fertilizers can minimize leaf-eating bugs. For extreme infestations, dissolve up to 5 tablespoons of a pyrethrin pesticide concentrate in 1 gallon of water, or follow label dilution instructions. Completely coat the lawn with the spray when the insects are causing active damage to destroy them.

Check the Thatch

Some insect pests cause the most damage in the thatch layer, which is the layer of decaying plant material beneath the grass leaves but above the soil surface. Moth larva caterpillars from armyworms (Spodoptera) and cutworms (Euxoa auxiliaris) cut off grass blades at the base, leaving behind bald or thin patches. Sod webworms (Crambus), another moth caterpillar, cause irregular brown patches from feeding on tender new growth near the crown of the grass plants. Removing the excess thatch when it becomes more than 1/2 inch deep minimizes thatch pests. Pyrethrin applications can also destroy and manage these pests when applied during the spring and summer feeding season.

Identification and Prevention Tips

Damage alone may not provide enough clues to properly identify the insects feeding on your lawn. Flooding a small section of the lawn with a mixture of 1 part dish soap to 10 parts water can force thatch and leaf blade pests to the lawn surface so you can more easily identify them. Monitoring for adult stages of the pests, such as increased beetle or lawn moth activity, can also provide identification clues. Keeping the soil moist but not soggy, and overseeding the lawn annually, helps increase the health of your grass so it's better able to withstand minor pest issues.