Summary: If you want your lawn to look nicely manicured, but it keeps developing dead patches, you may have just met your new worst enemy. The sod webworm is out to destroy your lawn despite your best efforts. Here's how to find out if you have a problem and what to do about it.
Although the adult sod webworm moth is not harmful to humans the larvae can wreak havoc on lawns and even some crops such as corn and wheat. This species of webworm mostly eats common turf grasses or sod, which is how it got its name. These pests can demolish the lawns of homes, golf courses and cemeteries where lush, green grass is preferred.
Sod webworms are also known as lawn moths because of its habit of flying low over the top of the grass. Webworms like hot, dry areas and avoid the grass areas that are more shaded or damp. It digs little tunnels made of silk and leaves that it lives in during the winter. The sod webworms can attack lawns as early as March, munching away at tender grasses and causing thin spots or areas of dead grass. Weeds often spring up in spots that have been attacked.
The larvae can grow up to an inch long. Its body can have different shades of browns and greens, and sometimes grays with dark spots. This great variety can make them difficult to distinguish from other worms. Adult moths are small, tan, and are cigar shaped when it rolls its wings around itself like a tube when at rest. It also has a snout-like protrusion coming from its head.
Finding an adult moth does not guarantee that you have a sod webworm problem. It is capable of flying long distances from where it fed as a larvae. However, finding flying moths may be a sign that you will soon have an infestation. Each adult female is capable of dropping up to 200 tiny eggs while it flies, spreading her eggs onto potential new territories. In a little over a week, these eggs can hatch and start feeding on your lawn.
The sod webworm is not too particular about the type of grass it feeds upon. It typically eats perennial ryegrass, Kentucky bluegrass and fine fescue. Resulting damages can be identified by thinning grass, as well as small patches of dead grass up to 3 inches in diameter. When larval activity is at its peak in the hottest parts of the summer, dead spots can appear so frequently that they may form an even larger area of dead or thinned out grass. The damages are often overlooked by homeowners because it has the same look as the damage resulting from high temperatures and lack of rain; both common summer conditions.
Look carefully through the grass in an affected area if you suspect you have an infestation of these pests. If you discover small green pellets, then you know you have sod webworms. The pellets, known as œfrass, are the fecal droppings left behind by the larvae.
You rarely find feeding sod webworm larvae because they feed at night. In order to locate the pests you can mix a little detergent into a gallon of water and spray it lightly over an area of turf that is beginning to brown. For your experiment do not pick a section of the lawn that is already dead because the larvae will have already moved to new feeding areas. The soapy water will cause the larvae to come out of its tunnels to the surface. If you find more than a handful of larvae you need to treat your lawn with a pesticide.
You have a variety of choices for treating for sod webworms. The first choice is water. Sod worms prefer dry ground and will not tolerate constantly damp ground. However, this can be hard to achieve in the middle of summer when it is very hot and over-watering can bring on other problems such as various lawn diseases associated with water and high humidity.
Another option is planting grass labeled œEndophyte Enhanced. This grass variety will be more resistant to the sod webworms.
To kill sod webworms outright, pesticides may be the final option. It is best to treat in the late afternoon so the larvae will be exposed to the pesticides during their night feeding. Be sure to select an insecticide that lists sod webworm on the label and follow application directions precisely.