Risk assessment of aerial transport of rust pathogens to the Western Hemisphere and within North America
The risk of aerial long-distance transport of rust pathogens from potential source locations in the Eastern Hemisphere to the Western Hemisphere and from subtropical to continental interior regions within North America is investigated. Simulations of longdistance transport of rust spores using the Integrated Aerobiology Modeling System indicate that the frequency of transport and deposition in the Western Hemisphere of viable rust spores originating from potential sources in tropical Africa, at high latitudes in Europe, and throughout eastern Asia is low. However, the frequency of trans-oceanic transport and deposition of viable rust spores in the Western Hemisphere is high for potential African source locations poleward of the tropics. The relatively short distance between Western Africa and northeastern South America coupled with the presence of persistent Northeasterly Trade Winds create an active pathway for spore transport. Western Hemisphere regions that are influenced by the Intertropical Convergence Zone have the highest likelihood of receiving viable rust spores from the Eastern Hemisphere. The risk of aerial transport of viable rust spores to U.S. regions from potential Eastern Hemisphere source regions is low. Analysis of wind streamline maps for North America indicate that strong low-level advection of air northward from the subtropics is prevalent east of the Rocky Mountains from early April to mid-May providing opportunities for long-distance transport of rust pathogens into the continental interior. After mid-June, the number of days with strong lowlevel advection of air from south to north across these regions and thus opportunities for long-distance spore transport decrease dramatically.