Establishing risk for alternative over-summering hosts for wheat curl mites and associated viruses

Wheat is grown on more land than any other crop around the world, and it 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, Wheat streak mosaic, Wheat mosaic, and Triticum mosaic viruses. All of these viruses are transmitted by the wheat curl mite (WCM). 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 became completely infested one week after harvest.  The greatest mite activity within the alternate host plots occurred in the barnyardgrass and foxtail millet, with lesser activity occurring in corn and green foxtail.