How to Kill Lawn Earthworms

Earthworms are considered beneficial to lawns because they help decompose organic matter. Some species, however, make mounds that detract from a lawn's appearance. This can be a special problem on a sports field or golf course. Be forewarned that as of 2009, no insecticides were registered for use to kill earthworms in the U.S. and federal law prohibited using pesticides other than as directed on the label. Check with your county extension service as to what insecticides are legal for earthworm use before purchase, and whether an exterminator license is required for application.

Things You'll Need

• Insecticide
• Fungicide (optional)
• Fertilizer

Instructions

1. Apply a carbamate insecticide such as carbaryl (Sevin), bendiocarb (Turcam), or propoxure (Baygon). The rate of application to kill grubs is adequate for earthworms: 4 to 8 pounds of active ingredient per acre. One application should greatly reduce the population for a season. The insecticide should be reapplied each season.

2. Apply a benzimidazole fungicide or carbamate fungicide if you prefer a natural approach that kills earthworms. Benzimidazole fungicides include benomyl, thiabendazole, thiophonate-methyl, and carbendazim. Carbamate fungicide brands include Bromosan WP, Bromosan F, Lesco Thiram, Spotrete and Thiramad.

3. Collect grass clippings to reduce the food supply for the worms. The drawback is this will reduce the return of nutrients to the soil. (Fertilizing a lawn with its own clippings is considered a cheap, effective form of fertilizer.)

4. Check for proper drainage, as poor drainage is where many earthworm problems tend to arise.

Tips & Warnings

• Maintain an adequate fertilization program, since killing off the earthworms will deplete your lawn of nutrients.

References

• Ohio State U.: Earthworms
• U. of Wisconsin: Earthworms: Beneficial or Pests?
• N.C. State: Earthworms as Pests in Home Lawns