Corn is a moderate host for both the virus and the mite. Although these species are extremely common in Kentucky, apparently none of them contribute significantly towards WSM epidemics. If they did, we would see more evidence of WSM each year. This thesis is backed up by observations and studies from areas where WSM is common. Then, if the volunteer wheat is not killed at least two weeks prior to the emergence of wheat in the same or adjacent fields, the mite will move onto the emerging wheat and spread the virus to the young wheat seedlings.
Mites move to the emerging wheat by wind.
Prior to the spring 2000 epidemic, there was an abundance of volunteer wheat in Kentucky because of poor weed control in doublecrop soybean due to the summer 1999 drought. Observation of many fields exhibiting WSM during 2000, in fact, showed an association with volunteer wheat in neighboring fields. However, this was not true in all situations and many fields that were severely affected by WSM were not closely associated with volunteer wheat. This suggests that mites moved into those fields from distant sources in wind currents. Another weakness in the link between volunteer wheat and WSM epidemiology is that many fields throughout the state had minimal WSM, even though significant volunteer wheat problems existed.