Winter grain mite outbreak reported

Roberts Diana

Farmers urged to check fields for signs of winter grain mite

By MATTHEW WEAVER

Capital Press

A tiny mite is causing big damage to bluegrass fields in Spokane County, Wash., and extension agents are urging farmers to check their fields.

A damaging infestation of winter grain mite was reported in a timothy grass field in Valleyford, Wash., on March 29. There are also reports of widespread infestation in Kentucky bluegrass fields in the county.

Spokane-based Washington State University Extension Educator Diana Roberts said the mite is seldom a problem in wheat, but can be more damaging in timothy and other perennial grasses.

In a press release, Roberts stated the mite is best viewed with a hand lens as it is only about 1 millimeter long. The body appears blue-black, roundish and has eight bright red-orange legs.

Damage appears as brown, round or oval-shaped patches in a field that should be greening up. Roberts said. Feeding damage appears on leaves as a light colored mosaic-type pattern with a silver cast. The leaf tips go brown and the whole plant may die.

Glenn Fisher, Oregon State University professor of plant and livestock insects, said the mite has occurred sporadically east of the Cascades in the grass and cereal regions of Idaho, Washington, Oregon, Nevada, Colorado and the Midwest. Local infestations can occur in some grass seed crops west of the Cascades in Oregon, he added.

The mites build up in no-till cropping systems and are spread by wind and farm machinery going from an infested field to a non-infested field, Fisher said. Small populations can be found in most grass and cereal fields, but the conditions that cause an outbreak are not well understood, he said.

Plowing, cultivation and post-harvest burning to remove straw used to provide adequate control of the mite and other pests, Fisher said.

The mites tend to multiply in a mild winter and spring, as Spokane has had, Roberts said. They peak around March or April, but will have laid eggs, which won't hatch until October. The dry fall conditions Spokane often has would inhibit hatching, she said.

Roberts advises farmers check several spots across their fields, especially borders with Conservation Reserve Program land or grass. Farmers should check at least 10 random sites within a field, and have hundreds of mites, as just a few do not warrant spraying, Roberts said. Spraying will kill any beneficial insects.

There are no organic controls for the mite, Fisher said. When a crop is treated, a synthetic insecticide registered on the crop is generally used. For grass seed and wheat, dimethoate and synthetic pyrethroid insecticides control the mite. For grass pastures, synthetic pyrethroid insecticides like Baythroid, Warrior or Mustang are used.

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