Pat Munts: Certain larvae infest summer lawns

Have brown patches in your lawn? You may be a victim of a lawn insect infestation helped along by the mild winter.

Adult crane flies resemble large mosquitoes and generally appear in late July into mid-October. They have a life expectancy of less than 14 days, but the larvae that hatch from the eggs laid at this time can create havoc in your lawn the following spring.

The larvae, or leatherjackets, are about an inch long and tan, gray or whitish in color. They begin feeding on sod roots in the late winter. As they feed, they kill the grass, which forms dead patches that can be mistaken for poorly irrigated grass.

If you suspect crane fly larvae, dig up a patch of sod and look for the larvae. The sod might even just peel back. The threshold for treatment is more than 20 larvae per square foot with treatments being made in late September as eggs are being laid, and in early April when the larvae become active.

Birds and insect-eating animals like skunks can often decimate a problem, although the skunks will leave holes in the yard. Our normally cold winters also knock back populations. Organic controls are limited, but there are a number of chemicals on the market that will control them. Remember that any insecticide for larvae control will kill honeybees and other beneficial insects, so follow label directions carefully.

Sod webworms create the same kind of visual damage to a lawn but have a very different life biology. The webworms are the larvae of a lawn moth that tends to fly a zigzag pattern over lawn areas, laying eggs in the evening in the early summer. The larvae are about three-quarters of an inch long, brown to green in color, with dark spots and a brown head. The larvae feed on grass blades in July and August and then pupate in silky cocoons in the soil. There is a second generation in August and September.

Biological control is done using the bacteria Bacillus thuringiensis (or Bt) or a beneficial nematode, but bird predation, disease and insect predators can do a lot of damage without your intervention. Chemical controls are readily available, but again, they can harm bees and beneficial insects, so read labels carefully and follow the directions. Controls must be applied when the webworm larvae is feeding.

Turfgrass cutworms are the larvae of a large miller moth, and their damage appears as small circles of grass trimmed close to the soil. The worms are around 2 inches long with wide brown, gray, or black bodies; some are spotted or striped. They feed at night starting in the early spring, leaving clipped grass and piles of fecal pellets.

If you think you have them, peel back a piece of sod and look for curled larvae. While birds will again gobble up the larvae, biological and chemical controls are basically the same as for sod webworms with the same cautions.