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Sod webworm damage to turf, July 1, 2003.
Sod webworms can be destructive to lawns if they are not monitored. Sod webworms are the larval stage of lawn moths. Lawn moths are small, dingy-white moths that fly around when you walk through the lawn. They have a wingspan of about ¾”. The moths are not what damages lawns, it is there larvae that is destructive. During late spring to early summer these moths are noticed. They fly around, dropping their eggs close to the thatch, preferably in moist areas with tender grass. The eggs look like tiny cream beads. In about four days the eggs hatch into larvae.
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The larvae are grayish-brown in color, about ¾” long, with four rows of dark spots on their underside. Nocturnally these worms feed on the blades of grass turning it brown and killing it. They build burrows in the thatch to live in, dragging the blades of grass into them, to feed on. Once the larvae have matured, they leave the burrow and construct cocoons made of silk in the thatch. In about ten to fourteen days the moths emerge out of the cocoons.
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Damage
Sod webworms cause brown patches of dead grass in lawns. You can tell that sod webworms are causing the damage if the blades of grass are missing, inferring that they ate the grass. Another indicator of sod webworms is that there will be green fecal pellets, or silk-lined tubes in the thatch.
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The best way to keep your lawn healthy is to monitor its stresses. Stresses like temperature, moisture, and insect presence can affect your lawn. By detecting pest insects, lawns can be treated correctly. There are many options in lawn care. There are grass varieties that are insect resistant that can be planted. Such grasses include ‘Park’ and ‘Windsor’ Kentucky Blue Grass. Also, there are endophytic grasses (grasses that contain beneficial fungi) that repel pest insects. Conserving native biological controls can decrease the number of pest insects. Biological controls that prey upon webworms include four species of ants, robber flies, birds, parasitoids, and pathogens. All of these treatments help prevent sod webworms from being present in your lawn. If you already have sod webworms there may be other treatments. Chemicals such as pyrethrins and insecticidal soaps will kill webworms, but they may also kill beneficial insects as well. Bacillus thuringiensis (BT) is a bacterium that kills sod webworms. It acts as a stomach poison when they ingest it on the blades of grass. The only disadvantage is that it will not affect the moths because they do not ingest the grass. A biological control that has proven affective is the use of beneficial nematodes http://www.biologicco.com/products/L&G%20scanmask.htm. Nematodes such as Steinernema feltiae or Steinernema carpocapsae have been found to destroy sod webworms.
Text copyright by Albert Pye, Ph.D., BioLogic Company http://www.biologicco.com/
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