Stay on Top of SDS

ST. LOUIS (DTN) -- Most soybean farmers would relish the thought of a rerun of the 2014 crop season -- except for sudden death syndrome (SDS). The sneaky soybean disease that stole yield in many parts of the Midwest last season is gearing up for a repeat performance in 2015.

Central Illinois grower Ken Franklin first noticed SDS symptoms in individual plants two weeks ago when mowing roadsides on his family's operation, Nation Farms. "You can't spot it from the windshield just yet," he said of the disease's distinctive interveinal chlorosis -- the yellowing of leaf tissue between veins. Follow-up scouting confirmed that at least half of his bean fields were showing plants infested with the fungus. "Those spots will probably keep getting bigger and bigger," he said. Leaf tissue on infected plants eventually dies and pods drop. Symptoms usually appear in patches within fields.

Cool, wet conditions this spring and summer have allowed the disease to thrive once again, said Iowa State University plant pathologist Daren Mueller. "I think SDS [sudden death syndrome] is going to be very similar to last year," he told DTN.

The disease is actually surfacing in Iowa fields two weeks earlier than it did in 2014, Mueller said. Growers should be vigilant about checking their fields in the coming weeks in order to best evaluate the performance of their soybean varieties and disease management decisions.

KNOW YOUR RISK

Like many Illinois growers, Franklin faced a dilemma this spring: plant beans early into dry soils or take the risk of waiting on rain? He opted for the dry route and headed into the fields in early May, just in the nick of time.

"If you didn't plant that first week of May, the next time you planted was June," he said. Shortly after planting, the skies opened up where Franklin farms near Taylorville, Illinois, and dumped twice the region's average rainfall through May and June. "The beans struggled from day one," he recalled. "It was cool and wet and they took a while to come up."

With maximum exposure to the SDS fungus lurking in the soil, beans planted in April and early May will be the first to show symptoms of the disease now, Mueller said.

In general, fields with a history of SDS will also be at highest risk this year, he added.

However, the soil-borne fungus can travel to new fields fairly easily by way of equipment, so don't assume you're safe if you didn't see it last year. Franklin's fields, for example, dodged the disease last year, even as neighbors' beans were struck hard.

PUT IN THE LEG WORK NOW

Since there are no in-season treatments for SDS, scouting now is critical for determining future management steps.

"The big things to do right now would be to know where it's at and to make sure it's SDS," Mueller said.

From a truck cab, it's easy to mistake SDS for another soybean disease known as stem canker. However, stem canker-infected plants show a general yellowing and dieback starting at the top of plants, instead of the interveinal chlorosis of SDS, he said.

To confirm that the yellow patches you're seeing are actually SDS, pull up a few stems and split them down the middle. The "pith" or center of SDS-infected stalks will be white. See this video from University of Wisconsin plant pathologist Damon Smith for more details on how to identify SDS in the field: http://bit.ly/….

PLAN AHEAD

Selecting soybean varieties with good resistance ratings for the disease is a grower's first and best line of defense, Mueller said.

Franklin plans to pull up his variety planting map and determine where the infected spots fall. "We'll definitely track it," he said. "We'll probably look a little harder at variety scores this fall."

Matching up infected patches in your field with actual yield monitor readings is a good way to evaluate variety performance, added Southern Illinois University plant pathologist Jason Bond.

"All varieties differ with regard to resistance," he told DTN. "Some can show symptoms but then don't have as much yield impact as others." So take the time to compare not only different varieties' performance, but also how the same variety performed in areas with and without the disease, he said.

Other preventative measures include long-term crop rotation, planting later into warm, dry soils, and tillage, but all come with caveats.

Research from Iowa State University plant pathologist XB Yang has shown that the SDS fungus can survive on corn residue, including corn kernels. A different series of studies led by ISU determined that only long-term rotations that move away from soybeans for three to four years can significantly lower the disease's presence.

Likewise, additional research led by ISU confirmed that delaying planting solely to avoid SDS did not pay off yield-wise, Mueller said.

Finally, long-term tillage studies by ISU researchers proved inconclusive, and the trade-offs of soil erosion and fuel costs might outweigh the benefits, Bond pointed out.

Two companies have now also released on-seed fungicide treatments designed to protect against SDS: ILeVO from Bayer CropScience and Mertect from Syngenta.

University trials of ILeVO last year showed that it did significantly reduce disease symptoms, and more trials are underway this year to evaluate Mertect as well, Mueller said.

Seed treatments might help manage the disease, but don't depend on them to prevent it, Bond warned.

"You will still see foliar symptoms and they are best used to complement resistant varieties," he said.

Emily Unglesbee can be reached at emily.unglesbee@dtn.com

Follow Emily Unglesbee on Twitter @Emily_Unglesbee

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