Window of risk for volunteer wheat establishment during the heading stages of wheat and the potential for wheat curl mite infestation

Wheat is an important food grain worldwide, and it is the primary dryland crop in the western Great Plains. The wheat-mite-virus complex is the largest cause of disease loss in winter wheat production in the western Great Plains. This complex consists of three viruses, Wheat streak mosaic, High plains, and Triticum mosaic viruses. All of these viruses are transmitted by the wheat curl mite (Aceria tosichella K.). Widespread outbreaks of this complex are often linked to volunteer wheat arising after hail that occurs prior to harvest. A study was conducted to determine the wheat head development stages when wheat is able to germinate 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 and 2012-13 growing season. 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 that wheat can germinate during the early milk stage and that 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). Field studies using a hail machine on Camelot and Pronghorn wheat at early, soft and hard dough stages showed a significant impact of variety and hail date on volunteer establishment. Germination under field conditions was heavily influenced by environmental conditions.