July 5, 2007 at 8:20 a.m.
The species of ants commonly found in lawns is the cornfield ant. They construct a small mound that is found in exposed sites in the soil as well as in the cracks of sidewalks, patio bricks, driveways, etc. Many mounds may be present in a lawn. Nests are found especially in places where the grass is thinning or the ground is bare. Their appearance can be unsightly in lawns but except for them dulling your lawn mower blades they are not harming the turf. They are just taking advantage of favorable nesting sites.
It is not practical to use chemical control for cornfield ants in a lawn. Even if control is successful, another nest may move back into the area later. The best control is to encourage grass to grow in the bare and thinning areas. According to Jeff Hahn, assistant extension entomologist at the U of MN, cornfield ants do not harm garden plants.
Field ants may also be found in lawns. Workers are up to half an inch in size and may be black or black and red. They construct craters that are a foot wide or larger. Also called the thatching ants, many workers are active on the outside of the nests. Their nests are frequently found where grass is growing normally. Field ants are not as common in lawns as the cornfield ant is. However, when they are found in lawns they are more unsightly due to their high mound.
We are fortunate not to have fire ants in Minnesota and so the risk of bites and stings are minimal. However, it is possible to be attacked by certain ants, such as field ants which are moderate size, and can bite when defending their nests. Pavement ants are also known to bite and sting if their nests are threatened. These ants would generally not be aggressive towards people otherwise. Also ants that nest in lawns close to buildings can enter structures to forage for food and water or to nest.
If it is necessary to attempt to control an ant nest in the lawn, first try pouring soapy water into the nest. Mix any type of soap with water so it is sudsy. You may need to treat nests more than once. If this does not work, try an insecticide. There are a variety of insecticides you can use to treat ant nests, such as permethrin as a liquid or granules, carbaryl (sevin) as a liquid or granules, or acephate as a liquid. Be sure to select a product that is labeled for treating lawns and always read and follow label directions.
PLANT CLINICS: Volunteer Master Gardeners will be available Mondays from 4:30-7 p.m., at the Extension Office in North Branch at 38780 Eight Avenue, to answer your gardening questions. You can also call 651-674-4417 during these hours to speak with a Master Gardener. If you visit our website at www.extension.umn.edu/county/chisago you will find instructions for handling samples.
VOICE MAIL: You can leave a question for a volunteer Master Gardener at 651-674-4417. Depending on the volume of calls, they try to respond within a couple of days. During office hours ask for the Master Gardener voicemail, after hours, select ext. 18.