In addition to earthworms, there are several insects that can create small mounds of soil above the surface of turfgrass. Usually such mounding is of minimal consequence and, in fact, is beneficial to turfgrass environments as it accomplishes the same thing as cultivation, aeration and top-dressing - only on a very small scale.
On occasion, however, the mounds can become a nuisance, especially on closely mown greens where they may interfere with putting and ball roll.
In such cases it is important to know the identity of the insect in question. Because mounds alone are difficult to identify, associated insects should be used for validation.
Look for insects directly associated with the damage in question. Sometimes these insects are difficult to find because they are nocturnal or because they live in tiny burrows beneath the mounds.
One suggestion is to use a small probe or trowel to dig beneath the mound to a dept of several inches. Quickly deposit the core into a glass jar and look closely for any insect that might be present. Be persistent. Groups of typical mounds seldom fail to produce at least one token specimen, by which an identification can be made.
Ants and ground nesting solitary bees can sometimes cause mounds to appear. Both of these insects are easily managed with the use of carbaryl, among other pesticides.
Some tiny beetles such as scarabs (Geotrupes) and ground beetles (carabids) also can tunnel and deposit soil in small mounds on the surface of the turfgrass.
The above photo was submitted, compaining of nuisance ‘mounding’ on a putting green. This was reportedly occurring on a daily basis on 6 greens during June. A subsequent sample of the soil below revealed two ground beetles that we commonly know as seed corn beetles.
Despite their name, corn seed are not the primary food source for seed corn beetles. Rather, they feed on other things that they find in the soil including other insects. We also know that they are highly attracted to and fly to lights at night. There are two generations per year, typically occurring in May/June and again in August.
Their appearance is more likely in cool, wet conditions, typical of this spring.
Management recommendations for these beetles usually include applying a surface insecticide as soon as mounds appear. Insecticides recommended for seed corn beetles control include any of the contact pesticides labeled for use in turf.
Tim Gibb, Turfgrass Entomologist
Doug Richmond, Turfgrass Entomologist