With the very mild winter that most of Indiana experienced so far, we are being asked about its effect on insect populations for this year. The consensus among turfgrass entomologists is that although insect populations were probably not especially hurt by low temperatures this winter, they probably have not benefitted that much either. Insect pests have developed behavioral and physiological strategies to get through even very cold winters, so the lack of cold this winter probably will not affect the kinds of pests we have this year. However, because the emergence of insects is tied directly with temperature accumulations, we do expect to see insects emerge much earlier during years with mild winter compared to more normal years. In fact, we are already seeing the late winter emergence of many arthropods such as lady beetles, clover mites, and crane flies that usually begin later in March. Take for example clover mites. We are already receiving calls about these very tiny mites (smaller than a pin head) that may occur in high numbers, first around windows, but later over entire walls of buildings.
Clover mites most often originate in turfgrass stands that are relatively young (2 – 5 yrs old), well maintained and fertilized. During the late winter and again in the fall time, these mites seem to migrate in large numbers and often end up inside structures, including homes. Clover mites are small enough to squeeze through the tiniest of cracks and openings in buildings, making it nearly impossible to seal them out. Turfgass grown right up to and in direct contact with building foundations can also facilitate their entry into structures. Although they are harmless to humans and pets, the presence of large numbers of these mites inside structures can be unsettling and attempts to wipe or sweep them from light colored surfaces such as walls often smashes them, resulting in brown/red steaks that can be difficult to clean.
The temporary application of double-sided tape around window sills can help stop migrating mites from gaining further access into affected structures, but once inside, these mites often become dehydrated rather quickly making vacuum cleaning of their tiny dead bodies one of the best options.
Clover mites are very tiny as can be seen on this ruler. To most people they appear as tiny, moving, black specks. Under magnification, however, they are reddish in color and have characteristically long front legs. This character helps separate them from the hundreds of other different mites.
Clover mites can be prevented from entering a home or building by using perimeter treatments. These may be either physical or chemical. A physical barrier can be established by separating turfgrass (where the mites feed) from the perimeter wall of the building. A strip of clean cultivated soil or stone, free of grasses, that extends 18 – 24 inches out from the foundation is usually sufficient to deter these mites from crossing. Ornamental plants that are not clovers or grasses may be added to increase the attractiveness.
Chemical barrier treatments may be applied to the outside foundation perimeter (three feet high and three feet out). Soaps as well as pyrethroid insecticides have been shown to be effective IF applied during the times that the mites are on the move.
Use of chemicals inside the home is not recommended. Remember that these mites do not directly damage the building nor do they bite people. Most consider them a simply a temporary nuisance pest and find that vacuuming or wiping them up with a soft sponge or wet cloth is sufficient. Be aware that they can smear and leave a red stain if crushed.
Timothy J. Gibb, Extension Entomologist
Douglas Richmond, Turfgrass Entomologist