Spider mites in wheat and corn
Order: Acari
Family: Tetranychidae
Description and life history
Brown wheat mite (Petrobia latens)
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 (1/3 inch) or more. The eggs are round and red when laid in cooler months, or white when laid in summer.
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. These mites spend the night in soil and feed on host plants during the day. They are cool-season pests and oversummer 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 eggs. Outbreaks are historically associated with dry weather events. More recently, outbreaks have been documented in the High Plains of the central United States, and periods of heavy rainfall can significantly reduce spider mite populations.
Banks grass mite (Oligonychus pratensis)
Banks grass mites are grass-feeding specialists 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. Adults have pigmentation along both sides and the rear of the body. 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. 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. Banks grass mites reproduce throughout the summer until the following fall when they return to winter wheat. While Banks grass mites mainly attack corn, they are also considered pests of wheat, sorghum, and turf.
Quick Facts
- Spider mites are tiny arachnids that have four pairs of legs as adults and six in early immature stages.
- The brown wheat mite (Petrobia latens) and Banks grass mite (Oligonychus pratensis) can infest wheat, and the Banks grass mite can also attack corn.
- These mites also can use wild and cultivated plants other than wheat as hosts.
- Drought-stressed plants are the most susceptible to outbreaks of spider mites. The most effective management approach involves adequately irrigating plants. Planting drought-resistant varieties is also recommended in areas prone to drought.
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
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.
Cultural control
Drought-stressed plants are most prone to outbreaks, and one of the most important management approaches for spider mites involves sufficiently irrigating crops. The use of drought-resistant hybrids may reduce the likelihood of spider mite outbreaks during periods of drought-stress. However, research suggests that drought-resistant hybrids should only be considered in drought-prone areas since spider mite outbreaks are equally likely to occur on drought-susceptible and drought-resistant varieties under optimal irrigation. In Colorado, winter wheat is more susceptible to Banks grass mite infestation in the fall if they are near maturing corn.
Biological control
Natural enemies exist for both species of spider mite, most notably predatory mites (Acari: Phytoseiidae). One species of predatory mite, Galendromus flumenis is associated with Banks grass mite in California date gardens. Although not tested in wheat or corn, laboratory research suggests that G. flumenis prefers to feed on eggs but will feed on all life stages of Banks grass mite, and that augmentative release of G. flumenis may help support management efforts. Furthermore, releasing predatory mites during periods of egg laying may increase their efficacy. In addition, releasing G. flumenis earlier in the day will minimize sun and heat exposure.
Chemical control
It is worth noting that applications of insecticides can trigger outbreaks of spider mites due to their impact on resident populations of natural enemies. This effect is especially pronounced during periods of drought-stress. In general, acaricide applications are less effective on drought stressed plants.
Brown wheat mite
Although available, chemical control should be used judiciously for managing spider mites. Furthermore, since brown wheat mite populations also decrease with sufficient precipitation, acaricide applications are not usually warranted during periods of rainfall. In addition, insufficient rain can reduce yields below the economic threshold for justifying chemical treatments.
Banks grass mite
To prevent infestations in wheat, applying insecticides to the margins of fields that border corn is often sufficient in preventing significant economic losses. However, insecticide efficacy differs among mite species so accurate identification is important.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
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
Peterson, J., R. Lloyd, G. Hirzel, K. Mollet, W. Crow. 2023. Evaluation of foliar pesticides for the control of banks grass mite in field corn, 2016. Arthropod Management Tests. 48(1): 1-2. Available https://colostate.primo.exlibrisgroup.com/discovery/fulldisplay?docid=cdi_crossref_primary_10_1093_amt_tsad079&context=PC&vid=01COLSU_INST:01COLSU&lang=en&search_scope=MyCampus_FC_CI_PU_P&adaptor=Primo%20Central&tab=Everything&query=any,contains,banks%20grass%20mite
Royer, T., T. Hess, K. Seuhs, A. Zarrabi, and W. Crow. 2022. Insecticide Evaluations for Control of Brown Wheat Mite in Winter Wheat, 2022. Arthropod Management Tests. 47(1): 1
Available https://colostate.primo.exlibrisgroup.com/discovery/fulldisplay?docid=cdi_openaire_primary_doi_51cbf0a53c470386eb88277b7c81d064&context=PC&vid=01COLSU_INST:01COLSU&lang=en&search_scope=MyCampus_FC_CI_PU_P&adaptor=Primo%20Central&tab=Everything&query=any,contains,brown%20wheat%20mite\\
Royer, T. 2021. Mites in Small Grains. Oklahoma State University Extension. Available https://extension.okstate.edu/fact-sheets/mites-in-small-grains.html#:~:text=Brown%20wheat%20mites%20are%20more,and%20withered%20(Figure%203).
Ruckert, A., J. Golec, C. Barnes, R. Ramirez, and D. Reisig. 2021. Banks Grass Mite (Acari: Tetranychidae) Suppression May Add to the Benefit of Drought-Tolerant Corn Hybrids Exposed to Water Stress. Journal of Economic Entomology. Available https://colostate.primo.exlibrisgroup.com/discovery/fulldisplay?docid=cdi_unpaywall_primary_10_1093_jee_toaa269&context=PC&vid=01COLSU_INST:01COLSU&lang=en&search_scope=MyCampus_FC_CI_PU_P&adaptor=Primo%20Central&tab=Everything&query=any,contains,banks%20grass%20mite
Sitz, R., E. Peirce, E. Luna, D. Cockrell, L. Newhard, F. Pearis, and K. Giles. 2019. Temperature Limits for the Brown Wheat Mite, in Colorado. Journal of Economic Entomology. 112(5): 2507-2511. Available https://colostate.primo.exlibrisgroup.com/discovery/fulldisplay?docid=cdi_openaire_primary_doi_dedup_6071cddb774d3f6a165abe5fdcd1d2ea&context=PC&vid=01COLSU_INST:01COLSU&lang=en&search_scope=MyCampus_FC_CI_PU_P&adaptor=Primo%20Central&tab=Everything&query=any,contains,brown%20wheat%20mite
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
Takamichi, K. et al. 2012. Susceptibility of the brown wheat mine, Petrobia latens (Müller)(Acari: Tetrany) to agricultural chemicals in carrot crops. (in Japanese).
Journal of the Acarological Society of Japan. Available https://www.jstage.jst.go.jp/article/acari/21/1/21_21/_pdf