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 (ARS) and the Animal and Plant Health Inspection Service (APHIS) of the United States Department of Agriculture (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," said ASA Chairman Ron Heck, a soybean producer from Perry, Iowa.

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 said. "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 said. "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 (EPA) 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 said. "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."

A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases

August 26, 2004
From: ProMED-mail<promed@promedmail.org>
Source: @griculture Online News, 21 Aug 2004 [edited] <http://www.agriculture.com>

Soybean rust found north of equator in South America

USDA officials earlier this week told the American Soybean Association (ASA) that Asian soybean rust has been discovered 5 degrees above the equator in Colombia, the farthest north the fungus has been found in South America.

"Confirmation of soybean rust above the equator signals the advancement of spores in the direction of the continental United States," said Ron Heck, an Iowa soybean grower and ASA chairman.

U.S. experts working to predict the spread of Asian soybean rust have said that once soybean rust moves north of the equator, conditions are more favorable for its movement into the U.S. July and August are the likely months of its arrival, according to Monte Miles, plant pathologist with the USDA Agricultural Research Service at the University of Illinois.

As the disease moves further north, the probability of getting soybean rust increases each year, Miles says.

Prevailing winds are part of what has kept rust south of the equator, along with the lack of a suitable host. Also, north of the Equator soybeans are planted in the spring.

"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 5 years or longer," Heck said.

[Soybean rust is caused by 2 fungal species, _Phakopsora pachyrizi_ [Pp], which is very aggressive, and the weaker _P. meibromiae_ [Pm]. Pm has been found in limited areas in the Western Hemisphere, and is not known to cause severe yield losses in soybean. Both native to Asia, they have also been reported from Africa, Australia, South America, and Hawaii, but neither is currently found in the continental United States. Pp was recently found 5
degrees (250 miles) north of the Equator, near Cali, Colombia. Colombian authorities have confirmed the presence of Pp in the country's Valle del Cauca region, north of the Equator. According to the Colombian Agriculture Research Institute (ICA), the fungus found in the Caloto, Buga and Obando municipalities is Pm, a causal agent of soybean rust, has been present in Colombia for several years. According to the USDA web site, Pm is present throughout South and Central America and the Caribbean and was initially reported in Puerto Rico in 1976. Symptoms of Pm and Pp on soybean are identical. In addition to the cultivated soybean, _Glycine max_, there are many other leguminous host species that are susceptible to Pp and Pm. Yield losses from soybean rust are reported to range from 10 to 50 percent in the Eastern Hemisphere (Japan, southern China, Thailand). In Taiwan, yield losses have been reported as high as 90 percent in selected fields.

Useful references:
<http://www.invasivespecies.gov/profiles/soyrust.shtml> <http://www.ipm.iastate.edu/ipm/icm/2002/6-24-2002/soybeanrust.html>
<http://www.hpj.com/dtnnewstable.cfm?type=story&sid=12460>
- Mod.DH]