Be on the Lookout: Winter Grain Mite Spotted in Fields

February 4, 2026

Winter grain mites on wheat leaves. — Winter Grain Mite crawling on a winter wheat leaf blade. Key identifying characteristics include eight redish-orange legs, dark bodies, and a yellow to red pore on the back.

The unusually warm and wet winter we have been experiencing in late 2025 and into 2026 has brought out some less-than-usual winter wheat pests. WSU Extension agronomists have been getting reports from field consultants and growers in Northern Lincoln County that winter grain mite (Penthaleus major) has been identified and is actively feeding in wheat. The mite, more closely related to arachnids than insects, often has two generations per year with each life cycle from egg to adult lasting about 100 days. The first generation may emerge as early as October and typically peaks in December or January with the right weather (wet and warm), with the second generation peaking in March or April. Damage maybe mistaken or misidentified as winter damage as the winter wheat leaves are yellowish and the plants are stunted.

Description in image caption. — Winter Grain Mite crawling on a winter wheat leaf blade. Key identifying characteristics include eight redish-orange legs, dark bodies, and a yellow to red pore on the back.

A man holding a green wheat leaf with brown areas up close. — Winter Grain Mites cause damage by feeding on the chlorophyll of cells by using their piercing-sucking mouthparts. Plant stunting, delayed growth, or death can occur under heavy infestations.

Cultural Control

After scouting fields and responding to grower calls, WSU Extension agronomist Aaron Esser noted, “Where a farmer went winter canola, fallow, winter wheat, the crop looks excellent with zero damage at this stage. In the field where the farmer went winter wheat, fallow, winter wheat, it is heavily infected and has a very yellowish appearance.”

A wide view of two winter wheat fields. On the left is a field that shows heavy crop injury from wheat grain mites. On the right is a healthy field. — Crop rotation shows striking differences in levels of infestation and crop injury. The field on the left is in a winter wheat-fallow-winter wheat rotation. The field on the right follows a winter canola-fallow-winter wheat rotation.

Brown wheat crop field. — Field scale view of damage caused by Winter Grain Mite.

Chemical Control

The distinction between mites and other insects cannot be understated; mites are more closely related to spiders than insects and most insecticides will not work for control. Pyrethroids like Lambda-Cy (active ingredient; lambda cyhalothrin) may have some activity against mites but have been shown to kill natural enemies, and can even stimulate mite reproduction, leading to flare-ups post application. Although chemical control options for winter grain mite are limited, dimethoate (a systemic insecticide and miticide) is expected to provide control when effectively delivered to mites when they are feeding. Mites prefer to feed during cool, overcast, moist conditions, and often feed at night, and applications during overcast conditions will maximize product efficacy.

Note: If wheat is listed on the label and no label restrictions apply, products may be used for winter grain mite under FIFRA Section 2(ee), provided all label directions for wheat are followed, including rates, timing, safety requirements, and harvest intervals.

Related Resources

WSU Small Grains Insect Resources

To identify between different mite species in wheat fields (o p e n i n n e w t a b )

To understand the lifecycle and control options (o p e n s i n n e w t a b )

Kansas State Wheat Insect Pest Management Guide (2025) (o p e n s i n n e w t a b )