Brown wheat mites increasing in wheat fields
The brown wheat mites have been building up in the southwestern counties of Kansas the last couple of weeks. Controlling these mites is fairly simple, but the real question is whether to treat or not.
Brown wheat mite damage can be quite severe when wheat is under drought stress. They can be especially prevalent in continuous wheat or where volunteer wheat was allowed to grow the previous season. They can be seen crawling around on leaves, on the soil surface and under debris/dirt clods during the day. These mites will easily drown if a driving rain of >0.3 inches occurs. Also, irrigating infested wheat fields can quickly reduce populations.
The brown wheat mites look like pepper sprinkled on the leaves and will quickly drop off when disturbed. During windy days mites will not be as easy to spot as they will be around the plant base. No real threshold exists for the brown wheat mite, however it usually takes >200 mites per ft of row to justify chemical control in a unstressed crop. If young wheat looks fairly healthy and is not drought stressed, then the wheat will likely outgrow the mite damage. This may be slightly less if the young wheat is beginning to show signs of drought stress and mite numbers are building. Heavy brown wheat mite feeding can cause the leaves to dry out and eventually die. Coupled with drought, severe infestations quickly kill young plants. The key is to 1) monitor fields for water stress and mite presence 2) determine if brown wheat mite infestations are large enough to warrant chemical treatment 3) decide if the crop has the ability to bounce back if mite populations were lowered. If drought is taking a heavy toll on the crop then chemical control may not be economical. Keep in mind that some insecticides used for mite control can negatively affect beneficials and this can affect their ability to control later insect infestations in the wheat. It’s important to note that the presence of white eggs means the mites will soon disappear and control is probably not necessary. The presence of red eggs means more are soon to hatch.
The winter grain mite (below) is another mite species that may be lurking in wheat fields this time of year. These mites can be confused with brown wheat mites, however their temperature preference, period of activity and color help to distinguish them. This mite prefers cool season grasses as well as winter wheat. They are far more picky about the weather, preferring cooler weather from just above freezing to 70F. The may be active during mild winters and can occasionally be found feeding under snow cover. Normal precipitation does not seem to thwart these mites, but heavy rains can reduce populations. They prefer to feed between dusk and dawn, but may also be active during a cloudy, cool day. During hot weather they may burrow down in the soil up to 4 inches. Their legs have a more pronounced orange-reddish color and they posses a dorsal anal pore. Their waste, in the form of a yellow liquid, can be seen exuding from the anal pore on top of their body in the picture below. The anal pore is located ventrally on the brown wheat mite. This can be seen with the help of a good hand lens.
For chemical control options, see here: http://www.ksre.ksu.edu/bookstore/pubs/mf745.pdf
Photo from Oklahoma State University Small Grains Extension