A damaging infestation of winter grain mite (Penthaleus major) was reported in a Timothy grass field at Valleyford, Spokane County, earlier this week (March 29)by Diana Roberts, Washington State University Area Agronomist. She also notes there are reports that infestations are widespread in Kentucky bluegrass fields in Spokane County. Farmers should check their fields without delay as this is the peak season for the pest. Affected areas appear as brown, circular patches in a field.
The mite is best viewed with a hand lens as it is only about 1 mm long. The body appears blue-black, roundish, and with 8 bright, red-orange legs. In 2009, Oregon State University Extension published a bulletin on the mite at
Hosts of the winter grain mite include many crops in the grass family, plus some broadleaved plants. It is seldom an economic problem in wheat, but can be damaging in perennial grasses such as Timothy and orchardgrass. Populations peak in March and April, especially following mild winters. Rain can reduce the mite populations drastically, especially in wheat. However, grass seed crops are more susceptible to prolonged damage.