Although asian soybean rust was first discovered in the United States in 2004, it has yet to inflict widespread economic disaster on the U.S. soybean market. However, Asian soybean rust still looms over U.S. soybean producers. “Under the right conditions, rust could have an economic impact in some regions,” says Robert Wisner, agricultural economist at Iowa State University.
What has worked in producers' favor the past two years is the weather. Spores have been found overwintering in the extreme southern United States, but the hot, dry weather — conditions that have plagued the Southeast over the past two years — has minimized the disease spread. Soybean rust prefers temperatures of 68° to 73° and 6 to 12 hours of wet conditions. “Just perfect for the disease to take off,” notes Eric Tedford, technical brand manager for fungicides at Syngenta.
Although the South has been dry, that's not the norm. “We have to be careful and not base our long-term understanding of how this disease works on the past two years,” says Gary Fellows, technical marketing manager at BASF. “A cool, wet spring in the South could significantly change the rust outlook for the growing season.”
What to watch for, experts say, is where rust is first detected. “Producers really need to pay attention to what's occurring in the southern United States,” says Shawn Conley, soybean specialist at Purdue University.
How quickly rust develops and moves into the Delta and south Texas, combined with the wind patterns, will dictate how the spores move. “If rust develops in Florida and South Carolina, past models indicate that Midwest producers aren't likely to see the disease,” Conley says. “But if we see the disease in Louisiana and Texas, wind patterns typically push the spores up through the Mississippi River, moving up through Arkansas, Missouri, Kentucky and into Indiana and Illinois.”
In 2006, soybean rust was found in 274 counties in 15 states, including Illinois and Indiana.
Producers have been aided in their soybean rust watch by a network of soybean rust sentinel plots scattered throughout the United States. These plots, which numbered 753 in 35 states last year, are the canary in the coal mine for producers on the lookout for rust. The entire industry has created this network to provide an up-to-the-minute assessment of rust spore movement.
Tools for control
The industry also has responded with an assortment of fungicides that work well as both preventative and curative sprays. “There are adequate supplies of chemicals available, and we have a good knowledge of the disease,” Fellows says. “There are a lot of excellent tools out there to control rust, and we've learned a lot more about the disease over the past few years.”
Disease management will depend greatly on location. For southeastern soybean producers, this could mean constant monitoring and preventative fungicide treatments throughout the growing season. This has been occurring, and producers have seen an additional advantage of controlling other crop diseases. “One thing that we have learned is that the fungicides available do a nice job of fighting a broad spectrum of diseases,” says Randy Myers, fungicide product manager at Bayer CropScience.
Farther north, however, the risk of the disease diminishes, and producers can take a wait-and-see approach. “But if soybean rust is starting to move, that's a different situation,” Myers says.
Each year, soybean rust finds its way further north into the United States. So far, the damage has been minimal. “Will soybean rust ever be a problem in the major soybean producing regions of the United States? Hopefully not, but it is still too early to know for sure,” Conley says. “Right now there is an early warning system in place, so the disease probably won't come up and bite us. Unless we stop looking for it.”