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Managing a nightmare soybean disease

DANIEL LOOKER 09/10/2010 @ 4:57pm Business Editor

It sounds like the plot for a cheap horror movie: For months, a monster lives buried in the soil, only to reach up and kill healthy looking soybeans, sometimes in broad swaths across the landscape.

That monster is a fungus, Fusariaum Virguliforme, the cause of Sudden Death Syndrome, a nightmare confronting growers across the Midwest this year. The disease starts in the roots and sends a toxin to the leaves that kills the plant. Foliar fungicides are useless against the toxin.

Cathy Schmidt, a plant pathologist at Southern Illinois University, understands the frustration of watching helplessly as SDS takes its toll.

"Sudden Death Syndrome is a disease of high yield. It appears when you have good conditions for growth," she tells Agriculture.com.

Schmidt should know. She coordinates the largest trial in the country of commercial soybean varieties for tolerance to SDS. The Illinois Soybean Association has been funding this trial for 25 years. At this point, there is no complete resistance to SDS, but you can sift through the thousands of varieties she has tested at this website. Generally, about 7% to 12% of commercial varieties are moderately resistant to highly resistant, which could still result in yield loss up to about 20%.

Seed selection is just part of the management options for anyone trying to avoid a sequel to the nightmare.

As Steve Butzen, agronomy information manager for Pioneer sums it up: "Management practices for SDS include selecting tolerant varieties, planting problematic fields last, managing SCN (soybean cyst nematode), improving field drainage, reducing compaction, evaluating tillage systems and reducing other stresses on the crop."

After a 2009 season that left some growers finishing harvest just before 2010 planting, this year brought a series of perfect storms for SDS.  A cool, wet spring favored growth of the fungus, with warmer weather later in the summer helping the toxin build up in leaves, says Aaron Robinson, technology development manager for Monsanto.

The fungus does especially well in poorly drained, compacted soils, a condition not helped by last year's wet harvest and this year's wet spring.

"Farmers just haven't had the opportunity to get out and take care of compaction," Robinson says.

X. B. Yang, a plant pathologist at Iowa State University agrees that improving drainage will help reduce SDS. "This only works in a normal year, not a year like this summer," he says. He, too, recommends delaying planting on problem fields. "This works all the time," he says.

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