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Watch out for SDS this summer
Is it going to be a bad year for sudden death syndrome (SDS) in soybeans?
There's good news and bad news. The bad news first: This spring's wet, cool conditions have been just about perfect for the disease to develop later on in the growing season, Iowa State University plant pathologists say in a report released Monday. Specifically, a wet June makes a huge difference in the prevalence and severity of the disease. In the last 30 years, the average June rainfall has averaged just over 26 centimeters for June in bad SDS years compared to 11.5 centimeters in non-SDS years, according to research led by ISU plant pathologist Daren Mueller.
"In this study, rainfall in April and May was similar in SDS years to non-SDS years. However, rainfall in June and July differed between disease years and nondisease years," Mueller says. "This highlights the importance of rainfall a bit later in the season to trigger the second phase of the disease."
Sudden death syndrome is a two-phase disease; the first phase, when symptoms comprise root rot earlier in the growing season, is the most common benefactor of cool, wet weather like the majority of soybean farmers have faced this spring. And, it's not isolated, timewise, to the early stages of the season.
"The early cool, wet weather we have seen so far in 2013 helps increase the root rot phase of the disease," Mueller says. "This can lead to development of severe SDS later in the growing season, as was seen in 2010 in Iowa."
Now for the good news. Even though the odds of the disease blossoming in this year's crop may seem high right now, time is still on farmers' side. The worst years for SDS are when the soybean crop is in the ground early, a far cry from this spring's planting season. In fact, the later the planting season stretches, the lower the odds that SDS will become an issue. Just don't assume you're out of the woods yet.
"One bit of good news for the 2013 season is that severe SDS usually is associated with early planting of soybeans. As many farmers are experiencing, the wet spring weather has delayed planting throughout the state. Fields with delayed planting should have less SDS develop in them," Mueller says. "However, we have found that research plots planted as late as June 15 still get SDS, so you are not completely out of the woods. SDS severity in these late-planted fields is very low, and much lower than fields planted in May."
Data from ISU show that in 2010, the last year SDS was a widespread issue, farmers nationwide saw a loss adding up to $1 billion because of the disease. Farmers in Iowa tallied almost one-third of those losses.