The American Soybean Association (ASA) has been alerted to a confirmed case of Asian soybean rust about five degrees north of the equator in South America. Earlier this week, the Agricultural Research Service and the Animal and Plant Health Inspection Service of USDA confirmed a report of soybean rust being identified north of Cali, Colombia.
"Confirmation of soybean rust above the equator signals the advancement of spores in the direction of the continental United States," says ASA Chairman Ron Heck, a soybean producer from Perry, IA.
Asian soybean rust has been present throughout Asia and Australia for decades. In 1996, the disease moved from Asia into Uganda, and by 2001, it had spread throughout much of Africa. In 2001, soybean rust was found in South America, and it has spread throughout the soybean growing areas of Brazil, Paraguay, and Bolivia. By 2003, rust had also spread to a northern, non-soybean growing area of Argentina.
"Prevailing wind patterns around the equator served as a temporary barrier to a natural transmission of soybean rust spores," Heck says. "If soybean rust becomes established on host plants in Colombia, South America, it would, at least theoretically, be easier for airborne spores to be carried directly to the U.S. across the Caribbean Sea, or by way of the land bridge formed by Central America."
Based on weather models and past experience with other diseases, the experts predict a natural introduction of soybean rust spores would most likely enter the U.S. through the southern tier of states along the Gulf of Mexico. Soybean rust spores are easily transported in air currents and spread rapidly over wide distances. Limited data are available on how long spores can survive, but studies have shown that under the right circumstances, spores can be viable for more than 50 days. It is also possible that the soybean rust spores discovered in Colombia were the result of commercial trade in soybeans from an infected growing area.
"The discovery of soybean rust north of the equator underscores the need for USDA to continue development of a national strategy for controlling and mitigating the potential for an Asian soybean rust infestation in the continental United States," Heck says. "Rust is a devastating disease with the potential to cause enormous losses in annual U.S. soybean production, resulting in serious consequences for domestic industry, including the livestock sector. We must do everything possible to be prepared to minimize the economic impact of soybean rust on the U.S. crop."
ASA has also been working closely with the Environmental Protection Agency to obtain approval of fungicide products to control soybean rust. Fungicide treatments currently represent the only option for containing soybean rust by lessening the spread of spores. Fungicide use in other countries has been effective in keeping soybean rust below the economic threshold of yield loss.
Early detection of soybean rust will be critical to minimizing the spread of the disease. To educate producers about soybean rust, ASA will continue its efforts to host seminars, distribute news releases and publish articles. In July, ASA completed a series of Soybean Rust Education Meetings in seven cities across the country.
"Because no one knows for sure when soybean rust will be introduced in the United States, we must work with the current knowledge that it could be a few months to perhaps five years or longer," Heck says. "During that time it will be important to maintain an on-going awareness campaign with ASA members to keep a response action in the forefront of their minds at whatever time they might suspect soybean rust has infected their crop."