Asian Soybean Rust
Asian soybean rust is a foliar disease caused by the fungus Phakopsora pachyrhizi. It is an aggressive disease capable of causing defoliation and significant yield loss. Asian soybean rust is found in most soybean growing areas of the world, and was found for the first time in North America in November 2004. Key points to know about Asian soybean rust
Spread of rust and the disease cycle Spores of the soybean rust pathogen are transported readily by air currents and can be disseminated rapidly hundreds of miles in a few days. Weather conditions will determine when and where the spores travel from south to north. Rust spores, called urediniospores, are able to penetrate the plant cells directly, rather than through natural openings or through wounds in the leaf tissue. Thus infection is relatively quick: about 9 to 10 days from initial infection to the next cycle of spore production.
Rust is a multi-cyclic disease. After the initial infection is established, the infection site can produce spores for 10 to 14 days. Abundant spore production occurs during wet leaf periods (in the form of rain or dew) of at least 8 hours and moderate temperatures of 60 to 80° F. Soybean rust has a wide host range Phakopsora pachyrhizi has a wide host range, which is unusual for a rust pathogen. There are more than 20 species of alternative hosts for soybean rust in southern U.S., including the common weed kudzu. Some other common hosts are yellow sweet clover, vetch, lupine, green and kidney bean, and lima and butter bean. The name Asian soybean rust is used to distinguish the soybean rust disease caused by Phakopsora pachyrhizi from a mild form of soybean rust, Phakopsora meibomiae , which is endemic to the Caribbean region.
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