Diagnosis For Webworms

Symptoms of Sod Webworms
Sod webworms cut grass blades off just above the thatch line, and they drag these blades into their silken tunnels to eat them. The grass in the damaged spots isn't just dead, it's been chewed off at ground level. In late spring the webworms’ feeding causes small brown patches, 1 to 2 inches in diameter, to appear in the lawn where the thatch layer is exposed. These dead patches may be round spots or may look like lightning bolt streaks running across the lawn. By midsummer the damaged areas join together into larger patches. Infested lawns look their worst by July and August. By this time, drought conditions may make it hard to tell the difference between water stress and insect damage.

Research has shown that if your lawn is in good condition, 2 to 3 webworms per square foot probably will not cause any problems. The worms will be kept in check by their natural enemies, including ants and spiders. However, if the lawn is stressed by compacted soil, drought or heavy thatch, even a few webworms will cause damage because the lawn grass is stressed and the webworm predator population may be low. Remedies are often applied too late, after most of the damage has occurred and the worms are ready to stop feeding and pupate. The worm eats about 70 percent of its total food supply in the last 10 days of its development. This is why severe damage can occur within a few days. Early detection, therefore, is important for successful control.

Catch Sod Webworms Early
Other factors such as disease, drought, and nutritional deficiencies will cause discolored areas in lawns. Therefore, examine your lawn carefully to determine what remedies are needed. To correctly diagnose the problem, look for sod webworms in the thatch layer in damaged lawn areas. Carefully break apart the thatch and search for their silken tubes. You also may find greenish-tan fecal pellets about the size of a pinhead, excreted by webworms. When lots of birds (especially robins) and even moles start feeding in your lawn, it may indicate a large population of webworms.

The Soap Drench Trick works on Sod Webworms: To determine if you have a large enough webworm population to require attention, mark off two sections of lawn measuring 2 feet by 2 feet in the early summer. Choose one damaged area and one undamaged area. Then mix 2 tablespoons of household liquid detergent into 1 gallon of water, and using a watering can, pour the solution evenly over each area. The soap will irritate any webworms in the turf, causing them to crawl to the surface in 5 to 10 minutes. Areas with thick thatch may require several gallons of soapy water for good saturation. If no webworms appear, the lawn damage is probably caused by disease or some other insect. Click here for more information on Dealing With Fungal Disease In Lawns .

see all questions...

Do you have a gardening question? Ask Nancy