Winter Mite Damage of Turfgrass

Photographs and Narrative by
Curtis E. Swift, Ph.D., Area Extension Agent (Horticulture)
Colorado State University Extension
Tri River Area

Mites are tiny, microscopic critters and many different types are found associated with turf. Some are predators feeding on plant-damaging mites; others inhabit soils under turfgrass and feed on fungi and decaying organic matter. The later help decompose plant litter and assist in nutrient cycling, while the former are active in biological control.

Plant-damaging mites are commonly found feeding on flowers, vegetables, brambles, junipers and other plants during hot weather. Not all mites that feed on plants, however, are hot-season pests. Lawns in Western Colorado occasionally exhibit damage resulting from the feeding activity of winter-feeding mites. When first infested the grass blades exhibit small yellow speckles. As the damage increases, the grass becomes straw colored and eventually withers and dies. The damage can occur under snow; dead patches appear when the snow melts. Snow does not appear to inhibit the feeding activity of the mites and may even provide protection.

The eggs of winter mites hatch in October, and their numbers increase into late winter. Eggs hatch when soil temperatures drop to 50 ^o F [10 ^o C]. The larval and nymphal stages feed by rasping the surface of the grass blades and sucking up the cell contents. The larval has six legs, while the two nymphal stages, referred to as protonymph and deutonymph, are eight-legged but smaller than adults (Tashiro).

It is not unusual to find several thousand mites per square foot. These heavy mite populations diminish in April when eggs are laid on dead grass plants and the adults die. This damage is often miss-diagnosed as winterkill or desiccation. Sever damage is more prevalent during warm winters.

The mites are easy to see with a hand-lens during late fall and winter months, but you need to check the base of the plant where these mites congregate during the day. Eggs are very tiny, about 0.005 inch (0.125 mm), so don't waste your time looking for these without a microscope. Where some grass mites feed on lawns during the summer, the ones we have problems with are those that feed during the winter. November would be a good time to get down on your belly on the lawn with your hand-lens to identify these pests. Lawns with a southern or western exposure are more susceptible to damage.

Whitney Cranshaw, Colorado State Extension Entomologist and John Pohly, former Extension Horticulture Agent, Boulder county, conducted research on the effects of fall and winter applications of water on winter grass mites. They concluded lawns watered in the fall and winter had significantly fewer mites and less damage than lawns that went into the winter dry.

A soapy water solution or miticide sprayed on the lawn in early winter helps reduce mite populations and the damage they cause. Organophosphates are also reported to be effective against this pest (Watschke).

Brandenburg, R.L. and Villani, M.G. 1995. Handbook of Turfgrass Insect Pests. The Entomological Society of America, Lanham, MD.
Leslie, A.R. 1994. Handbook of Integrated Pest Management for Turf and Ornamentals. Lewis Publishers, Boca Raton, FL.
Shurtleff, M.C., Fermanian, T.W., and Randell, R. 1987. Controlling Turfgrass Pests. Prentice-Hall, Inc., Englewood Cliffs, N.J.
Tashiro, H. 1987. Turfgrass Insects of the United States and Canada. Cornell University Press, Ithaca, NY.
Watschke, T.L., Dernoeden, P.H., and Shetlar, D.J. 1995. Advances in Turfgrass Science: Managing Turfgrass Pests. Lewis Publishers, Boca Raton, FL.

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Placed on the Internet May 16, 2002