Identifying and Preventing Sod Webworm Damage

The weather is heating up and summer is just around the corner. For our lawns this means making sure our irrigation systems are properly collaborated, our lawnmowers are in good working order, and any potential pest problems are dealt with before they become full-blown infestations. There’s nothing worse for a homeowner than witnessing your lush, green lawn transform into a brown, patchy wasteland almost overnight. This season is unique from other seasons. Due to our mild winter and warmer than usual spring, lawn pests are making an early start and wreaking havoc much earlier than normal. Already we have received several e-mails from concerned homeowners all over the country describing a similar problem; dead, brown patches in their otherwise lush, healthy lawn. There could be many reasons for these brown spots showing up in our lawns, but from the description of the damage given by most of our customers it sounds like the sod webworm is to blame. 

Eliminate Other Possible Causes

But before the sod webworm is automatically blamed for your lawn damage, it’s important to verify the source of the problem. The first thing to do when brown spots are found is to check lawn moisture to ensure it’s not an irrigation problem. To see if the brown area is getting enough water, stick a regular length screwdriver into the soil. If you can easily insert the screwdriver into the soil, your lawn is probably getting enough water. If it’s difficult to push in, it means the soil is dry and needs more water. Brown areas caused by irrigation problems tend to leave straight lines or are located in areas that sprinklers can’t reach, such as behind trees or in corners of your yard. Lack of nutrients, or too much nutrient in the case of fertilizer burn, may be to blame for brown spotty lawns. Lawn grubs could also be a reason for these dead areas in your grass. To identify lawn grub damage, check out this article. 

The biggest difference between grub and sod webworm damage is the way the dead grass feels when you pull it up. Since grubs eat the roots, when pulled on grass will crumble. There will be no resistance. If the damage is caused by webworms, the roots will still be intact although the grass will easily break off at the crown. 

Identifying the Adult Moth Form

The biggest indication you’ve got sod webworms is the presence of small, whitish moths that fly out of your lawn as you walk across it. These moths are the adult form of the sod webworm. They can be identified by their snouts which project out of their heads and usually fold their wings over their backs in a tube-like fashion when they’re not in flight. It’s not these adult moths that cause the damage; it’s their larvae (worms). During the day, sod webworm larvae lay low in the thatch layer. It’s only at night they become active and resume feeding on grass blades. After feeding for 4-7 weeks, the larvae form a silk cocoon and begin the transformation into the adult moth. After mating, fully grown female moths can produce around 60 eggs a day for 14 days. That’s a lot of new larvae to feed on your lawn! 

Identifying the Larvae (Worm) Form

Another way to verify a sod webworm problem is to find the actual larvae inside your grass. The larvae, or worms, range in size and color. Most are about ¾ inch long and have a brown head with a beige, gray, brown, or green body with circular spots and coarse hairs. To find the larvae, flush them out by pouring soapy water (2 tablespoons liquid dishwashing detergent into 2 gallons of water) over a 1 square foot area on the edge of the suspected area. In a moment the larvae should begin to crawl out of the thatch layer. 

Prevention is Better Than Cure

A lush, healthy lawn can usually tolerate a low to moderate sod webworm population without any noticeable damage to the grass. However, during times of stress and drought or in heavy infestations the damage may become visible. If not controlled it could lead to a severely damaged lawn. For heavy infestations or in situations where sod webworms have been persistent year after year, a professional lawn care technician can apply an appropriate pesticide, but ideally only after all preventative methods have been tried. Remember, an ounce of prevention is worth a pound of cure. The best way to handle sod webworms is to ensure they don’t even start to become a problem. To do this, try using a lawn grass that’s endophyte-enhanced, such as our Triple-Play Tall Fescue seed blend. Endophytes are fungal partners that live inside the grass and improve the overall vigor of the plant. These enhanced grasses can greatly reduce the possibility of sod webworm damage. 

A Healthy Lawn Can Resist Most Problems

It’s also important to maintain a healthy lawn. This is usually all that’s needed to keep most lawn problems at bay, from pests to weeds and even drought damage. Keep lawn maintained, but not overly maintained. Too much fertilization and irrigation can produce a lawn that is very attractive for female sod webworm moths to lay eggs. Beginning in the late spring you can begin inspecting your lawn for adult moths by walking across it at sunset and checking for larvae at the first sign of spotting in your lawn.