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Corn+Soybean Digest

Rust Alert

It wasn't the St. Valentine's Day Massacre, but when a Texas A&M plant pathologist found Asian soybean rust in a South Texas field on Feb. 14, there were immediate thoughts of how the find could devastate some Midwestern soybean fields that have dodged the bullet thus far.

The fear is prevailing winds will carry the Asian rust fungus spores northward into major soybean producing areas, meaning the chance for a bean belt outbreak might be higher than last year.

“Growers need to be ready like they were in 2005,” says Palle Pedersen, Iowa State University Extension soybean agronomist, in citing the need for Iowa and other Midwestern farmers to beware of rust potential.

“They need to monitor fields weekly and listen to their Extension personnel in their region and state. They need to be ready to react just like last year,” he says.

Marvin Miller, Texas Agricultural Experiment Station plant pathologist, discovered the rust outbreak at the A&M research station at Weslaco at the far southern tip of Texas. He and others suspect that the fungus entered Texas from Mexico. And it probably won't go away.

“It's here to stay,” says Miller. “It's a fact of life.”

Tom Isakeit, Texas A&M Extension plant pathologist, has further examined the rust outbreak. “Rust could be found on leaves throughout the whole field before the plot was harvested in early March,” he says. “But there are probably still rust spores entering the area.”

The same field was free of rust in mid December, so infection occurred in late December and early January, illustrating how the fungus likely moved northward from Mexico. Isakeit found no other signs of rust when scouting volunteer soybean seedlings 20 miles away and green bean fields 35 miles west of the site.

“With the exception of that one outbreak, there have been no other findings,” says Isakeit. “Our area sentinel plots will receive the next overview (this spring).”

Prevailing winds have been blamed for taking a number of other rust diseases on a northerly path, including southern rust of corn, stem rust of wheat and common rust of corn.

Isakeit notes that the finding in South Texas is probably a new introduction of the fungus. “What it suggests is that soybean rust could take the so-called ‘rust corridor’ to points possibly as far north as Canada,” he says.

Texas drought, while damaging to potential planting and production for virtually every Texas crop, could be a blessing for Midwestern growers. That's because dry weather hampers Asian soybean rust development.

If it turns wet, look out Corn Belt. “If it's dry, there is a good chance there aren't a lot of spores spreading. But if they have a rainy spring, those chances could increase,” says Iowa State's Pedersen. “There is no doubt that the probability of getting rust is greater for the Midwest when it's found in Texas than in Georgia or Florida.” He adds that the rust watch will likely intensify to help growers determine if and when spraying for rust is needed.

“We don't have a lot of foliar pathogens we can manage here in Iowa and in the upper Midwest. If you spray, you won't see any yield increase if there is no rust. But you don't want growers not to spray if there is a chance for rust,” he says. “That's why field monitoring is a must so growers can be prepared to make proper fungicide treatments.”

Pedersen says sentinel plots in Iowa and other areas are essential in monitoring Asian rust. “The plots are supported by the checkoff board and are important to us,” he says.

Isakeit says sentinel plots are being expanded across Texas, where even though soybean production is light, planting is widespread from the Panhandle to the Lower Rio Grande Valley more than 700 miles southward.

Information Isakeit and others obtain from the sentinel and other plots will be relayed to the USDA rust Web site at Additional rust Web links are at and at

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