The Q&A Archives: Lawn Pests

Question: My lawn has two problems: First, there is a small area that appears to be dead and I see insects which resemble large mosquitoes flying around and on the lawn. I was told these might be crane flies or leatherjackets. The other problem is the yellow mottling in my lawn--no specific patches; for the most part it is throughout. Could this be rust, and if so, what to do? We put our lawn in in the form of sod a few years ago, but unfortunately I don't know what kind of grass it is. It has always looked great until now.

Answer: Craneflies emerge in April and October in the Pacific Northwest. These giant mosquito-looking insects are sometimes called 'Daddy Longlegs'. They won't bite, and are not harmful to people, pets, or even other insects. Adult craneflies don't even eat; their main mission is to find a mate and lay eggs in the lawn. These eggs hatch and turn into larvae that develop a thick outer covering. That's where they get the nickname 'leatherjackets'. The larvae pupate just under the soil surface and when the weather is just right they wriggle up to the root area of lawns and feed on them. After growing to maturity they hatch into adult craneflies and fly around looking for mates. The damage in your lawn is probably caused by cranefly larvae. To check the population, take both ends out of a 2-pound coffee can (or similar sized container), sink it into the soil 3-4 inches and fill it with water. Leatherjackets will float to the top. When the water has drained, remove the container and count the bodies. If there are 25 or more, the infestation is high enough to warrant chemical treatment. If there are fewer than 25, the damage from their feeding will be minimal, and treatment isn't required. Now is a good time to rake any bare areas in your lawn and reseed with perennial rye or fine fescue grass seed.

The yellowing in your lawn may be due to a fungal disease, or due to the natural dormancy cycle of warm-season grasses. Since you don't know what grass types are planted, why not wait and see if the lawn greens up when the other, cool-season grass types begin their growth cycles. (Most lawns are a mixture of warm and cool season grasses to provide green blades all year around.) If there are still yellow patches in late fall, (November), you may want to take a sample to your local cooperative extension office for a diagnosis. (There are several locations in King County, so phone ahead to see which is closest to you: (206) 296-3900).

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