Mites in Wheat Fact Sheet No. 5.578 Insect Series|Crops by F.B. Peairs* Four species of mites attack wheat in Quick Facts Colorado: • The wheat curl mite, Aceria tosichella, • Four species of mites attack is a microscopic eriophyid mite of great wheat in Colorado. economic significance in Colorado. It • The wheat curl mite eggs, vectors the causal agents of wheat streak mosaic (Figure 1) and high plains disease. immature stages and adults • The brown wheat mite, Petrobia latens, are found in the winter on and Banks grass mite, Oligonychus wheat and nearby perennial pratensis, are spider mites that grasses. occasionally cause economic damage to Figure 2: Wheat curl mites in veins of wheat leaf. • Brown wheat mite summers in winter wheat in Colorado. Brown wheat the soil as a white egg. In the mite infestations normally are associated and eventually on green tissues in the head. fall, eggs hatch after a 10-day with dry spring weather and usually Eggs are placed along leaf veins. An average disappear with significant precipitation. complete generation requires eight to 10 days. incubation. • Banks grass mite becomes a pest of young Most mites are found on the upper surface • Banks grass mites produce wheat when it moves off maturing corn of the youngest fully expanded leaf, adjacent heavy webbing to protect in the fall, and less commonly in the late to the ligule. They seem to prefer the most colonies of eggs and adults. spring during droughty periods. tender leaf tissue and therefore move to each • Winter grain mite, Penthaleus major, also new leaf as it emerges. Leaf curling occurs • Favored hosts of the winter damages wheat, but is rare in Colorado. as a tight roll of the leaf margin, in contrast grain mite include small to the looser roll of the entire leaf caused by grains and grasses. Russian wheat aphid. As the wheat plant dries down, the wheat curl mites congregate on green tissue in the upper parts of the plants where they are picked up by wind currents and carried to their oversummering grass hosts. As summer hosts start to dry down, the reverse process occurs, and mites are carried by winds to newly emerged winter wheat. Host Plants. The wheat curl mite attacks a wide variety of grasses, mostly in Figure 1: Wheat plant affected by wheat streak mosaic. Photograph by R. Hammon. the Agropyron, Alamos, Hilary, Hordeum, Lolium, Muhlenbergia, Poa, Stipa, Triticum Wheat Curl Mite and Zea genera. Corn, volunteer wheat and summer grassy weeds such as barnyard grass, Field Biology. Eggs, immature stages and stinkgrass, witchgrass and green foxtail, are adult wheat curl mites (Figure 2) are found important oversummering hosts in Colorado. in the winter on wheat and other nearby Distribution. This mite is known to be perennial grasses. As temperatures rise in widely distributed in Europe and North the spring, mite populations develop under America, including the wheat-producing ©Colorado State University leaf sheaths, inside newly emerged leaves, areas of Colorado. It is likely found in most Extension. 9/99. Revised 12/14. wheat-producing areas of the world, since www.ext.colostate.edu wheat streak mosaic occurs in these areas. * Colorado State University Extension entomologist Scouting and Treatment. The only and professor; bioagricultural sciences and pest management. 12/2014 effective and economical controls for wheat Brown Wheat Mite yield may be so reduced by drought as to Field Biology. Brown wheat mite make chemical treatment uneconomical. (Figure 3) spends the summer in the soil as Also, if white eggs are present and red a white egg resistant to hot, dry conditions. eggs are mostly hatched, the population In the fall, as cooler, wetter conditions is in natural decline and treatment is not return, these eggs start to develop and economically justifiable. hatch after a 10-day incubation. Female mites mature after feeding on wheat for Banks Grass Mite about two weeks and then lay round, red Field Biology. Fertilized female Banks eggs (Figure 4) that give rise to further grass mites move into winter wheat in the Figure 3: Wheat plant damaged by brown wheat fall (one or two) and spring (two or three) fall as their summer hosts, primarily field mite. Mites can be seen on leaves. generations. Males have not been observed corn, begin to dry down. Overwintering in this species. As summer conditions mites are bright orange. With the onset return, white oversummering eggs are of winter conditions, the mites move to produced. Both red and white eggs are the crowns of wheat plants, where they placed on soil particles adjacent to wheat feed until spring. Small, pearly white plants (Figure 5). eggs then are laid that mature into pale to Brown wheat mites feed on plant bright green male and female adults. Mites sap during the day and spend the night Figure 4: Red brown wheat mite eggs, indicative breed continuously on wheat and summer of active population. in the soil. Their activity peaks at about hosts until their return to winter wheat midafternoon on warm, calm days (the in the following fall. The time required best time to scout). This mite is not affected to complete a generation varies with by cold temperatures, but populations are temperature and is usually 10 to 20 days. quickly reduced by driving rains of 1/3 inch Banks grass mites produce heavy or more. webbing to protect colonies consisting Host Plants. Damage from brown of eggs, immatures and adults (Figure wheat mite has been reported from a wide 6). Colonies usually are found on the variety of cultivated plants, including undersides of leaves. Damaged leaves first sorghum, onions, fruit trees, carrots, become yellow, then brown and necrotic. Figure 5: White brown wheat mite eggs, cotton, lettuce, iris, alfalfa and clover. In Heavy populations can kill small plants and indicative of population going into summer Colorado, this mite is considered to be a period of inactivity. reduce kernel size in larger plants. pest primarily of drought-stressed winter Host Plants. Banks grass mite attacks wheat and Kentucky bluegrass turf. a wide variety of grasses. In Colorado, it Distribution. Brown wheat mite is a is considered to be a serious pest of corn pest of small grains in most small grain- and an occasional pest of turf, sorghum producing areas of the world. In Colorado, and wheat. it is most common on drought-stressed Distribution. Banks grass mite has winter wheat on the eastern plains. been found damaging grasses in many Scouting and Treatment. Management parts of the Americas and Africa. It is of volunteer wheat is an important found throughout the grain-growing areas preventive measure for brown wheat of Colorado. mite, as it is with several winter wheat Scouting and Treatment. Banks grass pests. Any management practices that mite most commonly damages Colorado Figure 6: Banks grass mite female and eggs. serve to minimize drought stress are also winter wheat in the fall in areas near important. Once an outbreak occurs, maturing field corn. Insecticide applications curl mite are preventive, so scouting is not however, chemical control is the only to field margins bordering corn often are needed. Use preventive controls in high risk effective management. sufficient to prevent economic damage. areas where wheat was damaged by hail The economic threshold for this pest Spring infestations are not common in the after heading or where wheat will emerge is not well defined, but it is at least several state. Information on miticides registered before adjacent corn dries down. hundred mites per row-foot in the early for use against brown wheat mite can be Destruction of volunteer wheat and the spring. This figure will increase with found in the High Plains Integrated Pest maintenance of a two-week volunteer-free lower wheat prices and decrease with Management Guide, https:// period prior to planting winter wheat in higher wheat prices. It often is difficult to wiki.bugwood.org/HPIPM:Main_Page. the fall are the most effective management justify a chemical treatment, since brown practices for this mite and the virus diseases wheat mite infestations are associated Winter Grain Mite that it vectors. Some effective varietal with drought stress. If a driving rain of Field Biology. Winter grain mite resistance is available. at least 1/3 inch occurs, mite levels will has two generations per year. The first Control of wheat curl mites with be significantly reduced regardless of begins in the fall as the oversummering foliar acaricides has not been shown to chemical treatment. If it does not rain, crop eggs hatch after rains provide adequate be effective. moisture. Feeding peaks in December or Field Key to Mites January. Second generation feeding peaks Attacking Small Grains Chemical Control of in March or April. Populations decrease Mites in Wheat • Leaves with tightly rolled edges. Plants and oversummering eggs are produced as with chlorotic speckles or streaks, often • Scout and identify the pest species temperatures become unfavorably warm. stunted (symptoms of Wheat Streak Newly-hatched mites feed on leaf that are present. Mosaic) (Figure 1). Tiny, wormlike sheaths and tender shoots near the ground. mites, visible with aid of hand lens • Decide if it is economical to apply a Older immatures and adults feed higher up (at least 10X), present on leaves. chemical treatment. on the plants at night and on cloudy or cool Often found in spaces between veins days. They move to the soil surface and into • Consult the current High Plains (Figure 2). Wheat curl mite. the soil to seek moisture and to avoid warm Integrated Pest Management • Leaves finely mottled and may have temperatures. Winter grain mite activity Guide for Colorado, Montana, chlorotic tips (Figure 3). Heavily is greatest between 40 and 70 degrees F. infested crops have a droughty Western Nebraska and Wyoming, On hot, dry days, it may be necessary to appearance, or a yellowish to bronzed www.highplainsipm.org, for dig 4 to 5 inches into the soil to find the discoloration. On warm, calm days the treatment or treatment mites. The mites are not harmed by high brown mites with extremely long front combination that provides the humidity, rainfall, short periods of sleet or legs (Figure 3) may be found on leaves, best overall control of the pest ice cover, or by ground frozen to a depth of otherwise they can be found under soil problems that are present (for several inches. or surface debris. Brown wheat mite. Host Plants. Favored hosts include example, mites alone, mites • Leaves chlorotic, small plants may be small grains and grasses. Winter grain mite plus Russian wheat aphid, mites killed. Damaged areas on larger plants also has been reported to damage legumes, plus cutworms). The best choice may have a bright yellow appearance. vegetables, ornamental flowers, cotton, depends on the pest combination. Infested plants in the fall are often near peanut and various weeds. drying corn. Small green mites (Figure • Use at least 2 gallons per acre Distribution. Winter grain mite is 6) on leaves or in crowns. Produces total spray volume, especially if found in temperate areas throughout noticeable amounts of webbing on the world. Since it has higher moisture Banks grass mite is present in the undersides of leaves (brown wheat mite requirements than other mite pests of spring. also may produce small amounts of winter wheat, this mite is rarely a pest webbing). Banks grass mite. • Use a surfactant. under Colorado growing conditions. • Heavily infested crops grayish or silvery. Scouting and Treatment. Scout for • Buffer the spray solution to pH Plants may be stunted. Leaf tips appear winter grain mite early in the morning or 7 or lower. Dimethoate (various scorched and entire leaves or plants can during cool, cloudy weather when this mite formulations) should be buffered be killed. Absence of yellow mottling is most likely to be visible. Check for mites typical of spider mite feeding. A large to pH 5. under crust and clods on the surface of dark brown to black mite, with reddish moist soil under wheat plants. Under hot, • Treat when several hours of legs. A tan or orange spot is often visible dry conditions, scout several inches under temperatures above 50 F are on the back. Winter grain mite. the soil. expected, especially if using Little is known about winter grain mite dimethoate. management. Infestations probably should • Evaluate treatment effectiveness. exceed several mites per plant before chemical treatment is considered. Crop rotation is important.

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