Turfgrass Dead Spots. Insects?

Brown spots or dead areas in lawns can be common during the summer months. It might be a disease, but then again, it could be something else. Could it be insects?

The three primary reasons that lawns develop brown spots or dead areas are due to irrigation problems, the development of diseases and insect damage.

 Insect damage. Probably the least likely of the three, and the most easy to detect, is insect damage. Most of the lawns in the Las Vegas Valley are turf-type tall fescues. Tall fescue is not a sod forming grass like Kentucky bluegrass. Instead, each seed produces a single plant. These individual plants are not linked together like they are with Kentucky bluegrass. Kentucky bluegrass sends out rhizomes, or underground stems, that pop up a distance away from the mother plant. When these rhizomes grow together, they form carpet-like sod that holds together. Because tall fescue produces only one plant for each seed that was planted, individual plants are not linked together.

White grubs feeding on lawn roots of sod

            This is important when diagnosing damage to a lawn. Insects that feed on the roots of lawn grasses, like white grubs, will cause areas of dead or brown grass. Because the mother insect lays a lot of eggs in one area, insect damage is usually localized in one or two areas. The eggs hatch, the young grubs begin to feed on grass roots and the lawn develops brown patches that correspond to where the grubs are feasting. The roots are severed by the grubs and the grass cannot get enough water so it dies in patches during warm or hot weather.

One type of an adult of the white grub

            Insect damage by grubs is usually in spots that are fairly well defined. Because the roots are severed, the grass can be lifted from the soil quite easily. Because tall fescue are separate, individual plants the root-severed, brown grass lifts easily from the soil. In the case of tall fescue, the grasses lift from the soil in the independently and separately from each other. In the case of a sod-forming grass like Kentucky bluegrass, they do not. Because they are linked together, the damage area lifts like a carpet.

            When inspecting a lawn to determine if the damage is from insects or not, go to the edge of the damaged area, not the center of the dead spot, and pull on the grass plants lightly with a closed hand. If grubs causes the damage and it is tall fescue, many of the plants will lift easily in your hands; dead ones and green ones at the same time that were recently severed.