Ant Mounds in Lawns

This must be a particularly good year for ants to dig in lawns and cause unsightly, unwanted mounds, based on the number of calls I am receiving. There are many species of ants which occur in lawns and other turfgrass areas. Most are considered beneficial and do not require control. However, ants may become a nuisance by constructing mounds or small hills in the lawn or by invading the home from the yard in search of food.

The ants found in Iowa lawns are not biting or stinging pests. The fire ants of the southern U.S., well known for their aggressive behavior and painful stings, are not present in Iowa. Also, the noted mound building ants of the eastern U.S. (noted for building ant hills several feet in height) are not found in Iowa, although our local ants may build mounds several inches high and 12 to 24 inches in diameter if left undisturbed for a long period of time.

Soil nesting ants construct mounds or small hills by bringing granulated soil to the surface from the nest below. Mounds may be unsightly, may cause lawn unevenness, and if large, may smother out the surrounding grass. Ant mound building is highly variable from year to year and from place to place. It appears ants may be having an easy time digging right now because of the abundant moisture. Also, there are some places where ants just do very well, either because of soil conditions or colony strength.

Eliminating some of the worst ant hill activity may be possible by raking flat, on a regular and frequent basis, ant hills that appear above the grass tops during periods of prolific ant nesting activity (such as during periods of wet spring weather). For the worst cases it is possible to spot treat ant hills with insecticide. General lawn treatment specifically for ant colonies is seldom necessary.

Rake the ant hill flat and sprinkle diazinon or Dursban granules or Dursban dust onto the soil surface or drench the mound area with diazinon or Dursban diluted solution. If granules or dust were used, rake the area lightly after application and sprinkle with water. Keep children and pets away from the treated area until the grass has dried.

Rates: Diazinon labels are very clear about ant hill treatment; the amount of insecticide product per ant hill is specified (1 tablespoonful of 2% G or 1 1/2 teaspoons of 5% G or 2 tablespoonsful of 25% EC in 1 gallon of water per ant hill). Dursban labels only give guidelines for treating the whole lawn, and calculating a proper dose per ant hill is difficult if not impractical. For example, the Dursban 1% G label rate calculates out to 0.1 ounce of granules per square foot (approximately the size of an ant hill) -- whatever that means.

More than one application may be necessary for satisfactory control, though keep in mind that ant management rather than ant eradication should be the goal. If retreatment is needed, do not treat more than once per week or as specified on the label.

This article originally appeared in the May 12, 1993 issue, pp. 1993 issue, pp. 65-66.


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