Winter Grain Mite
Penthaleus major (Dugès)
Figure 7.16 Winter grain mite.
The winter grain mite, also known as blue oat or pea mite, is most prevalent from south-central Kansas through central Texas. Its host preferences are cereals and grasses, but it will feed on a wide range of broadleaf hosts as well. Recent taxonomic work in Australia with this mite has revealed the presence of two additional species, casting question on the true identity of this species in North America.
Identification / Life Cycle
Winter grain mites are about 1/25 inch (1 mm) in length with dark brown bodies (Figure 7.16). Their legs are reddish orange, and their front legs are only slightly longer than the others. Winter grain mite feeds at night or on cloudy days and readily drops from the plant when disturbed. When not on plants, mites may be found several inches down in the soil.
Winter grain mite spends the summer as dormant eggs. In the fall, these eggs hatch when soil moisture conditions are optimum, and a first generation peaks during early winter (December-January). A second generation occurs and peaks in early spring (March-April). Mites are most active between temperatures of 40 to 70°F (4-21°C), and they move into the soil during periods of warm, dry weather. The second generation produces the over-summering eggs that remain dormant until fall. The egg types (winter and summer) are difficult to distinguish because the summer eggs are only slightly larger. Both types of eggs are laid in the soil and on plant material, and when dried are wrinkled and tan.
Plant Damage / Response
Winter grain mites feed nocturnally, but remain near the plants during the day. Their feeding cause the leaves to become grayish or silvery in appearance as opposed to the typical yellowing caused by spider mite feeding. Extensive feeding can result in brown leaf tips and stunted or dead plants. Stunting will reduce potential forage in areas where wheat is grazed through the winter. Damage from the winter grain mite will be greatest during early winter (first generation) and again in early spring (second generation).
Winter grain mites are most severe in continuous winter cereals; therefore, rotation away from continuous winter cereals will reduce the risk of damage. If high mite numbers are present along with leaf damage and stunting, treatments may be warranted. Inspections for mite presence on the plants must be done when the mites are active (nights or cloudy days).