Risk for alternate oversummering hosts for the wheat-mite-virus complex in winter wheat

Wheat is the mainstay of dryland cropping systems in the western Great Plains. The wheat-mite-virus complex is the second largest cause of disease loss in winter wheat production in this region. This complex consists of three viruses transmitted by the wheat curl mite (WCM), Wheat streak mosaic, Wheat mosaic, and Triticum mosaic viruses. Widespread outbreaks of this complex are often linked to pre-harvest volunteer wheat; however, other grass species have been implicated as important oversummering hosts. A study was conducted to determine the potential for WCMs to survive on alternative hosts during the summer and serve as potential sources for mites and virus moving into fall-planted winter wheat. The primary host (wheat) and secondary hosts (corn, foxtail millet, barnyardgrass, and green foxtail) were seeded in small plots that emerged prior to winter wheat maturing. To monitor mite movement in each plot, sentinel wheat plants were grown under mite-free greenhouse conditions and exposed in the field for one-week intervals through the summer. Winter wheat was seeded around the plots in the fall to determine virus spread. Results indicate that mite activity across the plot area peaked as winter wheat matured, resulting in infestations in the treatment plots. Preharvest wheat plots were completely infested one week after harvest.  The greatest mite activity and virus spread from the alternate hosts occurred with barnyardgrass, followed by foxtail millet, with lesser activity occurring in corn and green foxtail. These results demonstrate the relative risk from these alternate hosts when adjacent to fall planted winter wheat.