Spatial interactions and management implications of the mite-virus complex in winter wheat

The wheat curl mite (WCM), Aceria tosichella Keifer, transmits three potentially devastating viruses to winter wheat causing significant yield loss across the Great Plains. Management of the green bridge period, or that period between wheat harvest and the subsequent emergence of winter wheat in the fall, is important to reduce virus spread to the new crop. An increased understanding of spatial components of mite movement through the landscape is necessary to determine the risk of serious virus spread into winter wheat. The WCM is very small (ca. 250 mm) making WCM dispersal very hard to monitor. However, the distribution of virus symptoms can be used to determine dispersal potential. Through the last several years we have undertaken a series of studies to provide a better picture of the dispersal potential of the mite and subsequent virus spread. The distribution of virus symptoms extended differentially in all directions from mite-virus sources, and this is influenced by wind direction and speed. However, dispersal potential has been found to be most highly dependent on mite density. Factors that influence mite density, such as host quality and temperature, are important in establishing risk levels for mite dispersal and virus spread.