Earthworms are beneficial for soil, but can be a pest when the castings are left behind on the ground surface. The castings will suffocate smaller grass blades. Worms on top of the lawn surface can disrupt activities on the grass. Eliminating the earthworms from the lawn may be a multiple-step process. There are no registered pesticides for killing earthworms in the soil. According to Ohio State University, pesticide treatments will only last one full season.
Remove undergrowth and thatch from the lawn by raking the grass vigorously with the lawn rake. Thatch is one of the primary food sources for earthworms. Thatch is dead grass and other organic materials that reside on the soil surface under the blades of grass.
Flatten the casting mounds with a lawn roller. This method will not rid the lawn of earthworms, but will smooth the irregular surface left behind by the worm castings.
Improve the soil drainage by aerating the soil. Lawn aerators remove plugs of soil from the lawn and redeposit it on the surface. Worm are attracted to less well-drained soils.
Decrease the soil pH level for the lawn. Worms will not inhabit soils with a pH level below 4.5. Conduct a soil test and use those results to reduce the overall soil pH. Contact your local agricultural extension service for process and procedures in soil testing and interpretation of the analysis.
Add the pesticide carbaryl to the lawn. Follow the label directions in application rates for grub control. Various strengths of carbaryl are offered, so rates applied to the lawn will vary. In general, 1.81 to 3.63 Kilogram of the product is applied over a full one-acre plot.
Keep people and animals from lawns treated with pesticides. Follow label directions for disposal of excess product.