ST. LOUIS (DTN) -- If you're looking for a silver lining to the appearance of sudden death syndrome (SDS) in soybeans again this year, Daren Mueller is your man.
Two years in a row of SDS presence have allowed plant pathologists across the country to rake in valuable data on how to best manage the disease, the Iowa State plant pathologist told DTN. So far, multi-year crop rotations and a new seed treatment are proving valuable tools, while tillage, late planting, and foliar fungicides have yielded less positive results in the field.
SEED TREATMENT SUCCESS
Bayer's ILeVO seed treatment targeting SDS performed well in field trials again this year, Mueller said. The product was available commercially for the first time in 2015, but researchers in Arkansas, Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Nebraska, Tennessee, Wisconsin, and Ontario, Canada have been testing it in fields since 2013.
After compiling these trial results, Mueller and his colleagues found that ILeVO added an average of 4.2 bushels to susceptible soybean varieties and 3.2 bushels to varieties with moderate resistance.
The treatment comes at a cost, however, so growers should calculate their SDS risk and losses carefully and check on their local seed dealer's pricing before taking the plunge in 2016. A grower in central Illinois contacted by DTN estimated its cost $11 to $13 an acre on top of the usual insecticide and fungicide treatments.
Generally, the worse the SDS outbreak, the more likely ILeVO will pay off, Mueller noted. The treatment appears to have a "sweet spot" of disease control in fields with a disease index between 10 and 20. Disease index is a 1-to-100-point scale that combines disease incidence and severity. At this level of disease, ILeVO averaged a 5.4 yield advantage and reduced SDS damage by more than 50% in the field trials.
With that in mind, growers who are weighing an ILeVO treatment in 2016 should target fields with a history of SDS and those slated for early spring planting. "We saw a drop in yield response for ILeVO in our June-planted trials," Mueller said.
No other SDS seed treatments or foliar fungicides tested in these field trials showed any effect on yield or SDS control, Mueller added.
ROTATE, ROTATE, ROTATE
The good news is that a 6-year crop rotation study from Iowa State has confirmed that crop rotation is an effective way to lower SDS damage.
The bad news is that the common two-year corn-soybean rotation of the Midwest isn't sufficient. The SDS fungus can survive and even thrive on corn residue, a phenomenon confirmed by Iowa State researchers in 2010.
"We saw the same trend we've seen over last five years -- the two-year corn-bean rotation had more SDS than the three-year rotation that added oats, and the four-year rotation that added alfalfa had even less," Mueller said.
The effect of tillage in Iowa State's field trials remains minimal, Mueller added. "We're in the fifth year of a trial comparing tillage and no-till in corn and soybean rotations, and every year the amount of disease in all three plots is exactly the same," he said.
THE EARLY BIRD STILL WINS
SDS is known to thrive in wet, cool soils, so planting later has often been touted as a good tactic to avoid infection. Mueller's planting date trials confirmed this again in 2015. Soybeans planted in early and late May showed more root rot than those planted in June.
Yet by the end of the year, the foliar damage from SDS was similar across all planting dates, Mueller said. "Soil temperatures actually had no effect on the amount of disease at the end of the year," he said. "What mattered more was the amount of rainfall we got in the summer months."
The yield advantage of planting early also trumped SDS damage, Mueller said. Beans planted in early May out-yielded their mid-June planted counterparts by an average of 12 bushels across 11 site-years of data.
You can read more about these field trials through the North Central Soybean Research Program, which funded much of this research along with the Iowa Soybean Association: http://bit.ly/….
Emily Unglesbee can be reached at firstname.lastname@example.org.
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