Published on Wednesday, 30 November -0001 00:00
By Janelle Kuechle,
U of M Extension
I have had several calls about treating ants in the home lawn. Homeowners have been reporting large numbers of ants in their lawns. Although their presence and volume may be alarming, their damage is usually minimal. When you see ant mounds in the lawn, the ants did not kill the grass, but instead are taking advantage of pre-existing problems in the lawn.
Cornfield ants are commonly found in lawns where they construct a small mound that is found in exposed areas in the soil as well as in the cracks of sidewalks, patio bricks and driveways. Many mounds may be present in the lawn, especially in places where the grass is thinning or the soil is bare. Although their appearance can be unsightly, these ants are not harming the turf. They are merely taking advantage of favorable nesting sites provided by the bare soil. A thick, healthy lawn will discourage ants. It is not practical to control cornfield ants in a lawn and the homeowners should tolerate nests that are present. If control is attempted, only try to eliminate ants from small areas in the lawn, sidewalk, patio or other area where they are most conspicuous. Seed or otherwise encourage grass to grow in areas where it is thinning to help discourage ants from establishing nests as well as making nests less visible. Cornfield ant mounds found in the gardens can be ignored. These ants do not harm garden plants.
Field ants, sometimes called thatching ants, are a second species that may be found in the lawns. Field ant workers are up to one-quarter inch in size and are either black or black and red in color. Unlike the small mounds constructed by cornfield ants, the field ants build a crater-like nest that may be a foot wide or larger. Field ants do not need bare areas to establish their nests and they are often found where grass is growing normally and even in tall, unmowed grass. Although they certainly are more of a nuisance than cornfield ants when found in the lawn, the field ant nests are not common in turf.
Jeff Hahn, University of Minnesota Extension Entomologist, states that management of ants in turf is difficult and at best only temporary. If nests are treated in an area, new nests will re-colonize that site after the insecticide residue dissipates. It is never suggested to attempt to treat all ant nests in a yard as you can never stay ahead of them. It would become an unending cycle of pesticide treatments, which is not practical or recommended. You can target a small number of nests that are particularly a nuisance or those that are located where the ants may cause a problem indoors. There are several insecticides that can be used to treat ant nests, including permethrin and carbaryl (Sevin) in both liquid and granular form; bifenthrin and cyfluthrin as granules; and acephate (Orthene) in liquid form. Be sure that the product you select is labeled for treating lawns and turf, and always read directions before applying.