April 20, 2012

Figure 1. Brown wheat mites on wheat. Figure 2. Brown wheat mites on wheat showing stippling injury and leaf-tip yellowing.

As many of you know, we have had a very dry start to the year in western Nebraska — precipitation levels are about 1-2 inches below normal. With these dry conditions we might expect increased mite activity.

This spring I have noticed brown wheat mites in some dryland winter wheat. Unfortunately, in severely drought-stressed wheat, there is little that can be done. The losses from drought stress will set back any gains that might be made by a chemical treatment against mites. Following is information on how to recognize mites, some of the environmental conditions that can drive down brown mite numbers, and what can be done to aid in their control.

Description

The brown wheat mite (Figure 1) is more typical in the drier climates of Colorado and Wyoming, but given the right conditions, it can become abundant in western Nebraska. Brown wheat mites are very small and red to brown in color. At a quick glance they may appear as tiny dark specs on wheat blades. Their injury results in a yellow to white stippling that is noticeable on the leaf blades. If severe injury occurs, leaf tips will begin to yellow or brown (Figure 2). Brown wheat mites can be found on a number of plant species and are more common on rain-parched land. These mites will migrate into the canopy during the day; however, they are weak climbers and are easily knocked off plants by wind.

The best management tool (as with many wheat insect pests) is good volunteer wheat control and any management practice that can minimize drought stress. If an outbreak should occur, only chemical control can reduce their numbers.

Scouting and Treatment

The best time to scout for these mites is mid-day and when winds are relatively calm. Economic thresholds for this mite are not well understood. It can be difficult to justify a chemical treatment as the drought conditions alone that are associated with this mite can severely limit yield regardless of mite activity. Furthermore, a single driving rain of as little as 1/3 inch can dramatically reduce mite numbers regardless of chemical treatment.

As the season progresses, producers and scouts should keep an eye out for the development of other mite species (for example, banks grass mites and spider mites) that benefit from this dry weather. Let’s hope we get some meaningful precipitation soon.

Jeff Bradshaw
Extension Entomologist, Panhandle REC