Soybean planting is a month or more away for most of the Cornbelt, but the nervousness about Asian soybean rust was recently heightened with confirmation that remnants of rust were found in soybeans stored in Iowa. Subfreezing temperatures have pushed living spores well to the southern parts of Florida and the Gulf Coast, but where do you stand this growing season? It is too late to obtain crop insurance for revenue risk management, so your production strategies are your only remaining alternative. What do we know about the enemy as we prepare for a possible battle this summer?

Those who lived through the Cold War were taught to fear “Ivan.” While the Soviet armies never attacked the US, it coincidentally was a hurricane named “Ivan” that brought soybean rust to the US in all likelihood. That was in September 2004, and soybean rust watchers found it in shortly thereafter in Louisiana. It appeared the next spring in Florida, after some of the hurricane-borne spores survived the winter on kudzu. Since then it has found its way to 15 other states, including the Cornbelt states of Indiana, Illinois, and now Iowa, as well as the states in the southern soybean belt. USDA plant pathologist Glen Hartman at the University of Illinois updated farmers and crop protection specialists. His report can be found on page 21 of the on-line proceedings of recent crop protection conference.

Hartman says 255 soybean producing counties had soybean rust confirmations last year as reported on the official USDA soybean rust website http://www.sbrusa.net and the occurrences increased from 2005 to 2006. He says research has increased substantially from the arrival of soybean rust in the continental US. Several findings will be important to the control of the fungus:
• The spores are sensitive to solar radiation, and Hartman says, “The relationship between spore viability and exposure to solar radiation is important to the soybean rust aerobiological model that provides North American soybean growers decision support for managing soybean rust.
• Spore release increased after leaves dried, peaked during midday, then tapered off toward the evening. Rainfall events reduced spore release for a 24- to 48-hour period.
• There are a variety of Asian soybean rust isolates found around the world, with different levels of virulence in attacking soybean lines that have some resistance to soybean rust.
• Quite a few hosts are being discovered for Asian rust, including lima, kidney, and other beans, however native legumes in the US have not encountered it.
• Seed samples from the soybean germplasm collection at the University of Illinois are being grown to look for potential resistant varieties, and so far 805 have shown some resistance. They are being tested in multiple geographic locations, and after being crossed with each other are being genetically mapped.
• A wild perennial relative of the soybean has show resistance, and its genes are being crossed with current soybean cultivars to introduce resistance to rust.
• For control purposes, fungicide testing in the US and Paraguay has focused on the efficacy of various fungicides, application technology and timing.
• Results showed that almost all fungicides controlled rust compared to the non-fungicide treatment, with yields often greater in fungicide plots than non-fungicide plots.
• In some locations, the difference between the two-application program and the three-application program was also significant, and these differences showed a trend where the residual activity differs among the products. In other locations in other years, trends varied depending on the onset and severity of rust.
• Data from the 2006 U.S. test plots with rust are currently being compiled, but, in 2005 in the test plots without rust, all but one treatment had significantly greater yield than the control at one location, and there was no statistical difference between the control and most treatments at two other locations.

Summary:
May researchers believed farmers “dodged the bullet” in 2006 by not having soybean rust problems, thanks to weather patterns and how far to the southwest Asian soybean rust successfully overwintered. Any change in weather or survival locations could mean a significant change in what producers will have to do this season to either prevent or treat soybean rust. There is a significant amount of research underway to discover potential prevention and rescue treatments, as well as an official website which provides daily information and recommendations for management.