Occurance and Attempts to Control Clover and Winter Grain Mites In Central Oregon Grass Pasture and Hay Fields

This mite probably should be controlled in April to prevent damage in more pastures with a history of imjury. Populations on certain orchardgrass pastures have steadily increased over the past 5 years in central Oregon; 2,000-3,000 mites/6-inch orchardgrass crown have been extracted from some pastures in April and May. Poor growth, chlorotic leaves, and even dead areas in pastures have been attributed to these mites. From a distance pasture grass injured by Clover mite is a more “yellowish” chlorotic than winter grain mite (Penthaleus major) damage and may resemble a fertilizer burn. The damage is particular noticeable shortly after spring regrowth should have begun. We began noticing large populations of this mite in orchardgrass pastures and hay fields in the Tumalo, Oregon area in 2000. Serious damage has resulted in the removal of many pastures and hay fields. Winter grain mite is also a cool season mite common on grasses and cereals in central Oregon in the fall and late winter. One generation occurs in the fall from eggs that oversummered in the field; a second generation occurs in late winter and early spring. The mites are most active at night and on cloudy, overcast days. Cereals, grasses, and many broadleaved plants are hosts. Over-summering eggs hatch in October. Mites have usually matured, mated and begin laying eggs in November. A female can lay 2-3 eggs/day and up to 60 in a lifetime. Ideal temperature for this mite is between 50 and 60°F. Peak activity usually occurs in December and again in February and March. It had been the only pest mite observed in any significant numbers on grasses and cereals up until 2000 in central Oregon. Feeding by this mite causes grasses to silver or turn dull gray. Often the leaf tips brown and die. Winter grain mite has damaged some orchardgrass and timothy hay fields in central Oregon. It seems to cause more damage to the grasses and cereals in the Jefferson County area, although more recently, winter grain mite and imjury has been identified in Deschutes and Crook County. Because significant damage has been attributed to the clover mite on these pastures, we surveyed chemicals and fertilizers that are registered for use on pasture grass in an attempt to select one or two for control of this mite. There are few products labeled with potential for mite activity based on available literature. Examples of chemicals found include malathion, cinnamaldehyde,