Winter Grain Mite

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Winter grain mites emerge at dusk to feed on grass leaves during the night.
Winter grain mite eggs are attached to dead grass stems or leaves.


  • Scientific Name: Penthaleus major (Duges). [Phylum Arthropoda: Class Arachnida: Order Acari: Family Eupodidae]


  • Common Names: winter grain mite


  • Climatic Zone: temperate


  • Geographic Distribution: The winter grain mite is a pest of small grains west of the Mississippi but is widely distributed throughout North America. It has been recorded attacking grasses, including Kentucky bluegrass, perennial ryegrass and fescues, especially in the northeastern United States. It is also found attacking cool season crops in Australia, China, Europe, New Zealand, South Africa, South America and Taiwan.


  • Damaging Stage: nymphs and adults


  • Hosts: Cool season grasses such as Kentucky bluegrass, ryegrass, fescues and occasionally bentgrass are common hosts. This pest also feeds on small grains and cool season vegetable and foliage crops such as peas, lettuce and clover.


  • Damage Symptoms: Cool season grasses such as Kentucky bluegrass, ryegrass, fescues and occasionally bentgrass are common hosts. This pest also feeds on small grains and cool season vegetable and foliage crops such as peas, lettuce and clover.


  • Description of Stages:


Eggs: Freshly laid eggs have a glistening reddish orange color. These are glued to the bases of grass plants, on the roots, or on pieces of thatch. After drying for a day the eggs become wrinkled and more straw colored.

Larvae: As with all mites, the larvae have only three pairs of legs. Larvae are reddish orange just after hatching but turn dark brown to black as they feed. The mouthparts and legs remain reddish orange.

Nymphs: Two nymphal instars are found. When the larva molts into the nymphal stage, a fourth pair of legs is gained. The nymphs look like the adults, olive black with reddish orange legs, but are smaller. The nymphs also generally have a more tapered abdomen.

Adults: The adults are relatively large for mites, up to 3/64 inch (1 mm) long. They are the only turf inhabiting mites with olive black bodies, reddish orange legs and mouthparts, a pair of white eye spots and a dorsal (opening on the back) anus. Only females are generally found though males have been reported.


  • Life Cycle and Habits:

The most distinctive feature about the winter grain mites' life cycle is the oversummering eggs and winter mite activity. In the northern United States, the mites appear to hatch in mid- to late October when soil surface temperatures are approaching 50 °F. The larvae feed by probing the surface of grass blades and sucking up the cell contents. Within a few days, the larva molts into the nymphal stage which feeds in the same manner for a week or two. Females can live up to five weeks during which they may lay 30 to 65 eggs.

The mites tend to hide during daylight and can be found clustered on the crown of grass plants, in the hatch and at the soil surface during bright, sunny winter days. Apparently snow cover does not inhibit feeding and may actually afford protection. Eggs laid from November through March usually hatch that winter but eggs laid from March on usually oversummer to hatch the following fall. It appears that two overlapping generations may occur during the winter with peak populations being found in late December and late February.

Winter grain mites often produce a droplet of liquid from the anus if disturbed. This may be a defensive action though undisturbed, feeding individuals also produce droplets. This mite is also very susceptible to desiccation, often becoming inactive and rapidly shriveling if moved to a dry spot.


  • Control Approaches: Damage by this pest is almost impossible to predict. When turf has been treated in summer with a carbamate insecticide, such as in cutworm or webworm control, winter grain mites often appear to increase significantly during the following winter. This may be due to a loss of predators or some other unknown effect.

Cultural Control - Mask Damage - Since this pest rarely kills the turf, the normally observed damage of spring silvering can be rapidly masked by applying a light spring fertilizer application in order to encourage rapid recovery of the turf.

Chemical Control - Early Applications of Miticides - Since it is hard to apply pesticides to turf under snow or in cold temperatures, treatment of the turf in the fall has been suggested. This has not worked well in the past though newer miticides are being developed which may prove useful in the future. If this approach is selected, sample in November and early December to determine that the mites are, indeed, active.

Chemical Control - Spring Applications of Pesticides - Most organophosphate and some pyrethroid insecticides as well as some registered miticides will satisfactorily kill this pest in the spring when temperatures allow spraying.

Monitoring

Winter grain mites are best detected as the sun is setting in November to December and again in February into mid-May. An insect sweep net can be used to scoop up the mites for an hour after sun setting or they can be simply observed by getting down our your hands-and-knees. The mites will often stain the hands and knees dark olive-green with some red markings. If the turf appears silvery as if from winter desiccation and mites are still active, control measures are warranted.