Irrigation Problem?Begin your investigation with the simplest test first. Perhaps the spot is caused by a lack of water. To test this, use a screwdriver to see if the dead patch is under-irrigated. Push the screwdriver into the suspect area. If it’s hard to push in, or won’t even penetrate the soil surface, the area is definitely not getting enough water. But if the screwdriver penetrates the soil easily and smoothly, irrigation is adequate. If you have an automatic sprinkler system, turn it on and observe the spray pattern. Most of the time the irrigation problem is simply a broken or clogged sprinkler head, or a pattern that’s not providing adequate coverage.
Lack of Sunlight?Is the area getting enough sunlight? Sometimes a chronic bare spot in your lawn is a sign that the area lacks proper sunlight. For this test, you’ll need to observe the area during a 24 hour period to see how many hours of direct sunlight the area is receiving each day. If the area is getting 8+ hours of direct sunlight each day, it’s considered full-sun. This is the ideal condition for most grasses. Part-sun and part-shade is considered at around 5-6 hours of direct sunlight. You can consider the area shady if it gets less than 5 hours of direct sunlight a day, and heavily shaded if it gets less than 3 hours per day. If it’s determined that shade is a problem, try seeding the area with a shade-tolerant grass species such as fine fescue. Keep in mind that no grass can survive heavily shaded areas.
Traffic Damage?Could the bare spot be the result of traffic? Dogs and other pets are often the cause of permanent bare spots throughout a yard. Erosion caused by constant running, rolling, digging, and walking can turn an otherwise lush green lawn into a muddy, dusty mess. Bare spots caused by traffic can also be due to lawnmower wear. For example, by mowing your lawn in the same direction every time, you can begin to cause bare spots in some areas. To avoid traffic damage, make sure you’re using a traffic-tolerant lawn grass such as Kentucky bluegrass, tall fescue or bermudagrass. Also switch up lawn mowing directions regularly and consider installing step-stones or pavers in the most heavily walked on areas.
Insect Infestation?The next few tests involve a little more work. Could the bare spot be the result of insects? Sod webworms are known for leaving dead patchy areas in a lawn. 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. 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. For more help dealing with sod webworms, see this article.
Chemical Spill?The bare spot may also be the result of a chemical spill. This is where your skills in interrogation and observation will come in handy as you attempt to discover who and what caused the dead or bare patch. Of course accidents will happen. When they do there are a few things you can do to help your lawn recover as quickly as possible. First, dig up any remaining dead turf from the area and dispose of it. Don’t place it in a compost pile since it will be contaminated. Next, dig up the first 4-5 inches of the soil and dispose of that as well. If possible, run a hose to the area and drench it for at least 20 minutes. This will help dissipate any chemicals that might still be in the soil. After this add fresh soil and reseed.