Sizing Up SDS

ST. LOUIS (DTN) -- The brown patches dotting Jeff Norton's soybean fields are no mystery to him.

The Hull, Ill., farmer has been managing Sudden Death Syndrome (SDS) in his Mississippi River bottom fields for at least two decades. This year even his standard preventative measures failed to safeguard some of his beans from the damaging soybean disease.

"SDS has been a problem for us for a long time," Norton told DTN. "Typically we'll sit around for a month, waiting to plant beans until the soil has warmed up, and that usually takes care of it. But boy, this year, it still came on strong."

Soybean farmers across the Midwest have reported high rates of the disease this fall. A cool, wet spring and early summer provided the perfect conditions for the soil-borne pathogen to infect young soybean roots.

The disease's symptoms are distinctive and surprising. Leaves turn yellow, then brown, and drop early. As the name suggests, plants die suddenly and the soybean seed is often smaller and more prone to shattering. Norton said the yield monitor often tells the tale, as patches of SDS will yield significantly less.

Harvest is a good time for growers to assess the extent of damage and make some important seed and management decisions for next year, plant pathologists told DTN. Variety selection, planting dates, soil compaction, soybean cyst nematode management and a new seed treatment can play a role in the development and intensity of the disease.

A GOOD YEAR FOR A BAD DISEASE

Late-season rainfalls flushed the SDS toxins up into the plants this summer, surprising many growers with the abrupt death of soybean plants that had promised a bumper crop up until then.

Weather conditions might have aligned well for an SDS outbreak, but Iowa State plant pathologist Daren Mueller said growers probably saw less damage than they could have. A dry stretch through the month of July slowed the disease in many states, he noted.

"I think that really pushed SDS development back into August, which reduced the amount of yield loss that it potentially could have had, because we had a really good spring and a really good June for it," he told DTN.

Past SDS outbreaks might have also aided farmers this year, Mueller added. After the 2010 outbreak, most highly susceptible varieties were easy for companies to identify and eliminate from their seed line-up.

PICKING SEED

Unlike most plant diseases, crop rotation is not a solution for SDS. The pathogen not only survives on corn residue, it thrives.

As a result, the pathogen will never leave your field once you have it. University of Illinois plant pathologist Carl Bradley said even growers who saw the disease for the first time this year or in small patches should still consider SDS-tolerant soybean varieties next year.

Evaluating the performance of his varieties this year will be especially important for Norton, who estimates that up to a third of his fields saw significant damage. Within the worst patches of infection, he expects 50% yield loss or higher.

"I try to pick varieties with best SDS ratings," he said. "It's the first thing I look at."

Farmers who grow soybeans in Maturity Groups II, III or higher should find a wide enough range of varieties with good SDS-tolerance ratings to not sacrifice other important traits like yield, Mueller said.

Options shrink in more northern regions where Maturity Group I beans are needed, but University of Minnesota plant pathologist Dean Malvick said growers should still be able to find what they need.

MANAGING FIELDS

Mueller is working on a series of SDS research projects mostly funded by Soybean Checkoff programs to evaluate the effects of management options such as cover crops, tillage, seed treatments and planting dates on SDS development and severity.

While Norton's late-May planting habits might not have saved the day this year, they remain a solid SDS preventative tactic, Mueller said.

Preliminary results from the study on planting dates suggest that putting beans in the field as early as late April or early May significantly increases the risk of SDS, he said.

Compacted soils can also force young soybean roots to linger in the infection zone too long and increase the risk of SDS. But don't run for the plow blindly, Mueller added.

"If you have a really bad compaction problem, that might be something that will contribute to SDS and then tillage might be an option," he said. "But if not, tillage is more likely to help spread pathogens more quickly across the field."

Research has shown that the SDS pathogen also has a cozy relationship with the soybean cyst nematode (SCN), so managing that difficult pest is important, Bradley said.

"My guess is a lot of people don't have a clue what nematode population level they have," he told DTN.

Norton says crop rotation has kept his farm's SCN populations low, but he plants cyst-resistant soybean varieties anyway, just to be safe.

An experimental seed treatment from Bayer called ILeVO has also shown promise.

Norton planted a test strip of ILeVO into cold, wet soils in early May, in what turned out to be an excellent testing year. Although he had to destroy the strip before it yielded because the product is not yet registered with the EPA, he said he was impressed by the results.

"I couldn't take it to yield to see how much actual benefit there was, but from a strictly visual standpoint, I sure saw a lot less disease," he said.

Mueller was equally optimistic. "It's holding up well under most of the scenarios where we're evaluating it," he said of their trials, which have tested the product with resistant and susceptible varieties, different planting dates, varying levels of inoculant, different types of irrigation, and a wide variety of herbicides.

In a February press release, Bayer said it hopes to roll out the seed treatment commercially in 2015, if EPA approval comes through by the end of 2014.

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

Follow Emily Unglesbee on Twitter @Emily_Unglesbee

(PS/AG/BAS)

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