Window of risk for pre-harvest volunteer during the heading stages of wheat

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 virus. All of these viruses are transmitted by the wheat curl mite.  Widespread outbreaks of this complex are often linked to volunteer wheat emerging before harvest. A study was conducted to determine the germination of wheat at different stages of head development and the ability of wheat curl mites to colonize this volunteer wheat. Wheat heads were collected from four varieties (Camelot, Mace, Millennium, and Pronghorn) at two separate locations during the 2011-12, 2012-13 and 2013-14 growing seasons. Heads were collected every five to seven days during head development. Each wheat head was staged, and placed on sterilized greenhouse soil in separate containers. After 21 days, wheat heads were evaluated for germination, plant height and mite presence. Results indicate wheat can germinate as early as the early milk stage, and germination potential increases after this stage. Mites were able to directly colonize the germinating plants during the later heading stages (i.e. after early dough stage). A follow up study was conducted in the field using a hail machine on Pronghorn wheat at middle milk, early, soft and hard dough stages. Results indicate that the germination of volunteer wheat was significantly impacted by wheat stage and environmental conditions.