Brown Spots in the Lawn & Worms

Many different things cause brown spots on the lawn. Grass-eating worms, however, are one of the most common causes. Although many worms work to help aerate the soil and promote healthy growth, some types actually kill the grass.

Worms which cause brown spots in the lawn include armyworms, sod webworms and cutworms, says the website All About Lawns. Armyworms and sod webworms are actually caterpillars which mature into moths. Their bodies measure less than an inch long, says Hobby Lawn Care. The only obvious difference between these two worm types and the cutworms is the way the cutworms curl into a spiral when exposed.

These pests feed off of grass and grass stems. This causes the grass to turn brown and die in large patches on the lawn if left untreated, says All About Lawns. They tend to like bluegrass, buffalo grass and bent grass varieties the best, according to Hobby Lawn Care.

Mix several tablespoons of dishwashing fluid with a gallon of water. If the brown patch takes up a very large area, double the batch. Dump the mixture over the brown spots and wait to see if worms surface. You have a worm infestation if more than four per square yard surface. Seeing the worms might help you identify which type of worm infestation you have.

Insecticides adequately treat grass-killing worms. Common insecticides for all three types include Dursban and Diazinon, says All About Lawns. These two work especially well if you don't know the exact worm type. The insecticides Orthene and Bacillus thuringiensis also treat cutworm and armyworm infestations.

Maintaining a healthy lawn best prevents grass-eating worms. Frequent dethatching and lawn aeration allows the grass to breathe and flourish. Watering also helps, especially during the summer months. Cutworms, sod webworms and armyworms all seem to feed off grass from the late summer months through the early fall.