Based on the previous three years experience, soybean rust's northward spread seems to take distinct routes. In 2007 the rust spread through the Great Plain soybean-growing region up to northern Iowa. Further examination found that this distinction was associated with the wind patterns supported by large-scale circulation. In the 2006 summer, a quasi-stationary cyclonic circulation anomaly was situated in the central-eastern U.S., whereas in 2007, an anticyclonic circulation dominated the central section of the U.S. Thus, whether there is cyclonic or anticyclonic circulation in the central U.S. is the key in determining the route of northward progress of the rust.