Ferns are leafy plants that are naturally found beneath forest canopies and in moist areas. Ferns reproduce from spores, rather than from the fertilization of a female plant by male pollen. Ferns are often used as ground cover and for landscaping, but they can also be a nuisance. Use herbicides to control the growth and spread of ferns.
According to the Michigan State University Department of Forestry, Asulam is effective in controlling the growth of bracken ferns for two or more years. Use one gallon of Asulam per one acre of actively growing ferns. Apply directly to the ferns without a wetting agent, and do not disturb the treated areas after the herbicide has been applied.
Control old world climbing fern (Lygodium microphyllum) by spraying affected areas with herbicide products that contain glyphosate or metsulfuron-methyl as the active ingredient. The Florida Exotic Pest Plant Council recommends that glyphosate herbicides should contain at least three to four pounds of glyphosate per gallon of solution, and metsulfuron-methyl herbicides should contain at least two ounces of metsulfuron-methyl per 100 gallons. Apply these herbicides separately or together. Treated ferns can take three weeks to six months to die, and treated areas should be monitored regularly. Visit treated areas at least twice a year, and re-treat any active growth immediately.
Washington state's Thurston County Environmental Health Division recommends using herbicides that contain dicamba as the active ingredient. Dicamba is effective in killing ferns, but will not damage surrounding grasses. Treat ferns with dicamba herbicides in late winter, and follow up with a second treatment in early summer. Use herbicides that contain dicamba in large, open areas only.
Most ferns require canopied areas and regular watering in order to flourish. Kill ferns without the use of toxic herbicides by covering them with a tarp, and pinning the edges down with rocks or bricks. Heat from the sun will become trapped underneath the tarp, which will dry out and kill the ferns.