Asiatic soybean rust, caused by Phakospora pachyrizi, was found in the United states in 2004 and likely came from South America with hurricane Ivan in September. Soybean loss as a result of rust was negligible in North America in 2004 because it arrived so late, but this disease has emerged as a major constraint to soybean production in South America since 2001.

During the 2003-2004 growing season in Brazil, Asiatic rust was severe in many areas and required sprays of fungicides in order to control this disease. The extent to which the soybean rust pathogen threatens future U.S. soybean crops is unknown. Predictive models suggest that conditions in the southeastern US are favorable for epidemic development most summers, while conditions are generally less favorable for disease in the mid-western and northern states are less favorable.

The soybean rust pathogen is primarily tropical in distribution and is likely to survive over winter in only the most southern portions of the US (Gulf of Mexico States). Spores of this fungus will not tolerate freezing temperatures. Rust spores will have to be transported by wind from these areas, or possibly the Caribbean each year to infect soybean. Soybean rust may survive on alternate hosts such as kudzu, winter vetch, white clover, many bean species, and lupines.

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