Banks grass mite (Oligonychus pratensis)
Brown wheat mite (Petrobia lateens)
Winter grain mite (Penthaleus major)
Pest description and crop damage These three mites are pests of many grasses and cereals east of the Cascades. Adults are tiny, brown to green, and have eight legs. Eggs are small, round or oval, white, and laid on leaves. Mites feed by puncturing and removing contents of epidermal cells of leaves. This results in a grayish cast to the field. Individual leaves are "stippled." Large populations of Banks grass mite build through the summer, having four or five generations before harvest. Timothy and bluegrass can be injured. Seed yield losses up to 50% have been reported under heavy infestations. Adult winter grain mites are dark blue to black with orange-red legs. Infested fields look grayish or silvery due to the destruction of epidermal cells and removal of plant sap and chlorophyll. Large populations of mites may begin to build in late September and continue through the winter. Another generation is in the spring and may injure grasses through May before over-summering mite forms are produced and the population crashes. Seedling grasses can be stunted or die if large populations infest seedling stands in the fall and if the winter is exceptionally cold. In western Oregon, the incidence of this mite has increased greatly in grasses grown for seed, particularly in direct seed and no-till seedling fields. In the fall, direct seeding of grass into a previous grass crop provides seedling grasses for the mites to crawl on as the previous crop dies down. Seedling stands can be lost if the mites are not controlled at this stage.
Biology and life history Winter grain mite survives hot, dry summers in the egg stage. In early fall, the over-summering eggs hatch (late September to early October). Mites mature in about 2 weeks. Two or three generations occur in the fall and early winter when temperatures are above 40°F. In eastern Oregon, Washington, and Idaho, populations may continue to develop slowly through the winter, under insulating snow cover. Damaging populations usually peak in late November. A second and third population peak can be from late winter through early spring.
Scouting and thresholds Inspect fields in October and November for presence of mites. On bright and/or windy days, mites usually are not on grasses; instead, they are in or on the soil, in soil cracks and crevices and along roots. From dusk until dawn on still evenings and on cloudy, overcast days, they feed on the leaves' epidermal cells.
No thresholds are established in grasses grown for seed. If the field generally looks off-color, grayish, or chlorotic, determine whether mites are the cause and treat accordingly.
- bifenthrin (Brigade 2EC and WSB) at 0.1 lb ai/a. Apply when mites appear, generally late-winter and early spring. Maximum amount allowed is 0.2 lb ai/a per season but no more than once every 14 days. PHI 30 days prior to harvest for forage, hay and seed.
- lambda-cyhalothrin (Warrior) at 0.02 to 0.03 lb ai/a. PHI 0 days for grazing and cut for forage, 7 days for straw and seed crop. REI 24 hr. Suppression only.
- lambda-cyhalothrin/chlorantraniliprole (Besiege) at 6.0 to 10.0 fl oz/acre. PHI 0 days for grazing and cut for forage, 7 days for straw and seed crop. REI 24 hr. Suppression only. Do not exceed a total of 27.0 fl oz of Besiege or 0.09 lb ai of lambda-cyhalothrin or 0.2 lb ai of chlorantraniliprole per acre per year.
- Note: dimethoate and chlorpyrifos (Lorsban Advanced), although effective for control of winter grain mite, do not satisfactorily control these two species.