Spider mites in wheat and corn
Order: Acari
Family: Tetranychidae
Description
There are two agriculturally important spider mite species in Colorado:
- Brown wheat mite, Petrobia latens
- Banks grass mite, Oligonychus pratensis
Quick Facts
- Spider mites are tiny arachnids that have eight legs as adults, six in early immature stages.
- Brown wheat mite and Banks grass mite can infest wheat, and the Banks grass mite can also be a pest of corn.
- These mites can use wild and cultivated plants other than wheat as hosts.
Adult of brown wheat mite. Brown wheat mites are pests of winter wheat. Image credit: Phil Sloderbeck, Kansas State University, Bugwood.org
Banks grass mite is a pest of wheat and corn. Image credit: F.C. Schweissing, Bugwood.org
Crop injury caused by brown wheat mite. Image credit: Phil Sloderbeck, Kansas State University, Bugwood.org
Injury to sweet corn caused by feeding of Banks grass mite. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Life history and habits
Brown wheat mite
In Colorado, brown wheat mites are most active on drought stressed winter wheat grown in the Eastern Plains. Brown wheat mite populations quickly decrease during periods of heavy rain of 8.5 mm or 1/3 inch or more.
Brown wheat mites can use a variety of cultivated plants other than wheat as a host. These include sorghum, onions, fruit trees, carrots, cotton, lettuce, iris, alfalfa, and clover. Brown wheat mites spend the night in soil and feed on host plants during the day. They are cool-season pests and over-summer in the soil as white eggs that are resistant to heat and desiccation. In the fall when conditions are cooler and wetter, the eggs hatch after an incubation period of about 10 days. Females spend two weeks feeding on wheat and then begin to lay round, red eggs that produce fall and spring generations. Females produce white eggs when summer returns.
Banks grass mite
Banks grass mites are found throughout the grain producing areas of Colorado. They primarily use corn as a summer host and migrate to winter wheat when corn begins to mature and dry out. These mites overwinter as brightly colored orange adults in the crowns of wheat plants. They feed until spring and begin to lay small white eggs. Banks grass mites reproduce throughout the summer until the following fall when they return to winter wheat. A single generation completes development in 10-20 days.
Banks grass mite colonies are typically found on the undersides of leaves. These mites produce webbing to protect the eggs, immatures, and adults in a colony. Webbing is also used to disperse to new hosts. While Banks grass mites mainly attack corn, they are also considered pests of wheat, sorghum, and turf.
Injury
Brown wheat mite
Feeding injury resembles symptoms of drought stress. Brown wheat mite infestations cause wheat to become withered and scorched or bronzed in appearance. It is important to inspect symptomatic crops for mites by shaking plants over a white piece of paper, which dislodges mites and allows for their detection.
Banks grass mite
Feeding causes leaves on the host plant to turn yellow and brown, eventually leading to leaf necrosis or dieback. Heavy infestations of Banks grass mite can kill smaller corn plants and cause a reduction in the kernel size of larger plants. Plants displaying yellow spotting and silvery coloration on lower leaves indicate mite activity. When symptoms are present, plants should be inspected weekly, if not more frequently, especially in warm and dry weather. Near the base of the plant, examine the underside of all leaves regardless of whether webbing is present. Look for small moving dots; shaking plants over a piece of white paper can help with this. Randomly sample and inspect leaves to determine the extent of mite activity in the crop.
Management options for spider mites in wheat:
Brown wheat mite
Acaricide applications are not as effective on drought stressed plants. Since brown wheat mite populations also decrease with sufficient precipitation, acaricide applications are not usually warranted. Furthermore, insufficient rain can reduce yields below the economic threshold for justifying chemical treatments.
Banks grass mite
In Colorado, winter wheat is more susceptible to Banks grass mite infestation in the fall if they are near maturing corn. Applying insecticides to the margins of fields that border corn are often sufficient in preventing significant economic losses. However, insecticide efficacy differs among mite species so accurate identification is important.
References
Cranshaw, W.S. & D.C. Sclar. 2014. Spider Mites. Colorado State University Extension – Fact Sheet 5.507. Available https://extension.colostate.edu/topic-areas/insects/spider-mites-5-507/
Cranshaw, W. 2013. Insect and Mite Galls. Colorado State University Extension – Fact sheet 5.557. Available https://extension.colostate.edu/topic-areas/insects/insect-and-mite-galls-5-577/
Davis, R. 2011. Eriophyid Mites: bud, bluster, gall and rust mites. Utah State University – Cooperative Extension. Available https://extension.usu.edu/pests/uppdl/files/factsheet/eriophyid-mites2010.pdf
Royer, T. 2021. Mites in Small Grains. Oklahoma State University Extension. Available at Oklahoma State University Extension
Sloderbeck, P. E., Michaud & R. J. Whitworth. 2018. Wheat Pests. Kansas State University: Department of Entomology. Available https://entomology.k-state.edu/extension/insect-information/crop-pests/wheat/curlmite.html
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.