Written with contributions by Shelby Pritchard, former SDSU Extension Pest Management Specialist.
Originally Submitted: June 9, 2022
There have been reports of brown wheat mites active in wheat in central and western South Dakota. The brown wheat mite is generally more of an issue in more-arid parts of the state, or in areas experiencing drought. They are currently being reported in areas of the state that are experiencing drought (Figure 1). The feeding injury caused by these mites leaves white or brown spots, called stippling. The stippling caused by the brown wheat mite generally begins near the leaf tips, and is very similar in appearance to drought symptoms. To date, reports have been for minor infestations, but severe infestations are possible. Fields that are heavily infested by the brown wheat mite often appear to be undergoing severe drought stress, with dried leaves and withering plants (Figure 2).
Brown Wheat Mite Description and Biology
In general, brown wheat mites are quite small and are approximately the same size as a newspaper print period. Identification of brown wheat mites may require a 5 to 10X hand lens. They get their name due to the metallic brown/black coloration of their bodies. Brown wheat mites have a total of eight legs that are light yellow/orange. The front pair of legs is nearly twice as long as the other three pairs of legs and can be used for identification purposes (Figure 3). Brown wheat mite activity is greatest in the early spring, and populations generally peak in South Dakota in mid-May. However, with the cool spring that we experienced in South Dakota, it is possible that brown wheat mites may remain active for a few more weeks in 2022. Brown wheat mites produce two different colored eggs depending on the season. Both eggs are found in the soil near the base of wheat plants. Red eggs are produced in the fall, and the amount of unhatched red eggs can be used as a predictor of whether a population outbreak is going to occur, or if populations are in decline. In late spring, the females produce white eggs that will over-summer and hatch in the fall.
Scouting
When scouting a field for the presence of brown wheat mites, start at one side of the field and walk in a W or zig-zag pattern and randomly choose plants to examine. Brown wheat mites are generally found on the leaves, and populations may be higher near the tips of the leaves. Plants should be examined from several locations present on the W or zig-zag pattern. See Table 1 for the economic thresholds for the brown wheat mite.
Management
If brown wheat mite populations are above the economic threshold, management may be necessary. Prior to insecticide application, check the weather forecast. The brown wheat mite favors drier conditions, but populations may naturally decline in the presence of precipitation. If a driving rain with more than 1/3 of an inch occurs, populations may be removed from the plants. For insecticides that are currently labeled for brown wheat mite, please refer to the current edition of the South Dakota Pest Management Guide: Wheat.
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