Although the No. 1 soybean disease concern for Iowa this past growing season was white mold, another very bad one was sudden death syndrome (SDS), says X.B. Yang, Iowa State University (ISU) soybean pathologist. “For this coming season, no one knows what the top soybean disease problem will be,” says Yang. “However, SDS prefers a cold, wet spring, like we had last year.”
When spring is cold and wet, soybean growers need to be concerned with SDS and seedling diseases like Pythium and Fusarium seed rot, cautions Yang. “While we don’t yet know what the temperatures will be like this spring, we do know that soils are definitely going to be wet,” he says. “So, it’s quite possible that SDS will again be a problem in Iowa and surrounding states.”
SDS has been spreading in Iowa every year since it was discovered to be present there 17 years ago, notes Yang. “It’s typically more of a problem in eastern Iowa, which tends to be wetter than western Iowa,” he says. “It’s been a recurrent problem in central and southern Illinois as well – for most of the time when SDS has been bad in Iowa, it’s been bad there, too.”
Up until more recent years, SDS was typically a more regular disease concern in southern soybean-growing states, but it has now spread to northern soybean-growing regions in Minnesota, Wisconsin and Michigan, points out Yang. It’s also starting to be a problem in Nebraska, where soybeans are intensively irrigated, he adds.
The main difficulty for soybean growers when SDS appears is the absence of an effective control treatment, says Yang. For now, there is no truly SDS-resistant variety available for farmers to plant, he adds.
“There are SDS-tolerant varieties, which offer some, but not complete, resistance to the disease,” says Yang. “Soybean growers in northern maturity zones will have fewer SDS-resistant varieties from which to choose, and the varieties will be less consistent in their tolerance to the disease than varieties from southern maturity zones.”
Still, soybean growers can do more than just select varieties with some resistance to SDS to minimize potential yield reductions from this disease, says Yang. “In fields where you have a history of SDS, wait to plant them last, when temperatures are warmer and soils are drier,” he advises. “Also, if you can tile your fields to improve drainage, that will help to reduce problems with SDS.”
Where you haven’t yet seen SDS, keep an eye out for it, especially in fields that have been infested with soybean cyst nematodes (SCN). “SDS typically follows where SCN goes,” says Yang. “Usually, four or five years after SCN becomes a major production problem, SDS becomes a major problem, too.”
Yet, fields can still have SDS without having SCN, points out Yang. “Unlike SDS, dry and warm soils favor SCN,” he says. “On the other hand, many studies have shown that managing fields for SCN will reduce the occurrence of and damage from SDS.”
This spring, if soils are both wet and cold, farmers might consider using soybean seed treatments for diseases other than SDS, suggest Yang. “A seed treatment might not be a bad idea to protect against seedling rot diseases this season,” he says. “However, current seed treatments don’t yet work for SDS.”
More information to help soybean growers manage SDS can be found in a new publication, Sudden Death Syndrome: Finding Solutions for Farmers, which is available online from the North Central Soybean Research Program. Farmers can also obtain more information from Yang on potential soybean disease problems in Iowa throughout the growing season by regularly checking the ISU’s crop management newsletter.
For more advice from Yang on controlling soybean disease problems during a cool, wet season, click here: http://www.extension.iastate.edu/CropNews/2009/0710yang.htm.