Bean Disease Review

SDS, White Mold Stand Out in 2015

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Did your beans suffer from sudden death syndrome, white mold or other diseases in 2015? Time to plan ahead for 2016. (DTN photo by Pamela Smith)

ST. LOUIS (DTN) -- The final soybeans of 2015 are hitting the bins, but your fields may be far from empty.

For the second year in a row, soybean diseases thrived in Midwestern fields and they've left their mark -- or rather, their fungus -- behind to keep the party going in 2016.

White mold was especially prominent in the upper Midwest, thanks to some bin-buster bean conditions, said University of Wisconsin plant pathologist Damon Smith. "We call it the high-yield disease," he told DTN. "The weather was really conducive for it throughout bloom period -- nice and cool and humid and wet."

Sudden death syndrome was another common complaint for farmers this year, though a later arrival of foliar symptoms ensured that the majority of fields fared better than 2014, said Iowa State University plant pathologist Daren Mueller.

So what can growers do now, as combines head to the shed?

Don't rest.

"Review the season," Mueller urged. "Go through which fields had problems, and figure out what varieties worked and which ones didn't. It's simple but it does matter."

For growers who had SDS, white mold or other diseases, varietal resistance will be the first line of defense in 2016. No varieties have perfect resistance to SDS or white mold, but you can find ones with good tolerance to the diseases, Smith said.

The next best protection is crop rotation, but both white mold and SDS will survive the two-year corn-soybean cycle, Mueller and Smith pointed out.

Research from Iowa State in 2010 proved the SDS fungus can survive on corn residue, so while crop rotation can help, one year to corn is unlikely to completely eliminate inoculum in the field, Mueller noted. Reducing white mold inoculum likewise requires multiple years of rotation to corn, small grains or other non-hosts, Smith said.

Tillage is often touted as a solution to SDS, which thrives in cold, wet, and compacted soils. However, a long-term tillage study at Iowa State has showed no effect on SDS for the fourth year in a row, Mueller noted.

Reduced tillage might actually lower white mold levels, Smith added. "We have some data that shows that no-till systems actually help with white mold because after a couple of years, you exhaust the viable inoculum in the upper portions of the soil," he said.

As you eye seed for 2016, keep in mind that lower seed populations and wider row spacing is another proven option for preventing white mold, which benefits from the moist, protected rows of a crowded soybean crop.

For growers struggling with SDS, Bayer's new seed treatment, ILeVO, has shown a consistent yield protection in university trials where the disease is present, Mueller said. The treatment comes with a cost, so Mueller recommends reserving it for fields with a history of the disease.

Many growers reported a phenomenon known as the "halo effect" in beans treated with ILeVO this season. The edges of soybean cotyledons turned yellow or brown and there was some concern that pre-emergence herbicides increase the phenomenon. Fortunately, soybeans outgrow the discoloration, and it does not appear to result in any yield or stand reduction, university plant pathologists concluded in an Iowa State University publication. (See the article here: http://bit.ly/…)

For more help with managing white mold, see this University of Wisconsin article: http://bit.ly/…, and for help with SDS, see these management guidelines from Purdue University: http://bit.ly/….

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

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(PS/AG/CZ)

Emily Unglesbee