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14 new counties see SDS strike soybeans

In 2010, Minnesota farmers and researchers found soybean sudden death syndrome in 14 new counties, bringing the total number of confirmed counties with SDS up to 37.

“We found it further north than we thought we would, up in Ottertail County,” says Dean Malvick, University of Minnesota plant pathologist. “Unfortunately, the conditions that favor high soybean yields also favor SDS.”

Malvick notes that in 2010, SDS appeared in many fields in established counties where it had never been seen before. Most affected fields had distinct hot spots, ranging from one-quarter acre to many acres. Plus, in southern Minnesota, researchers saw clear differences in susceptibility in some cultivars.

SDS is one disease that growers cannot ignore. Soybean yield losses range from 5% to more than 50%, depending on the weather, plant stage when infected, the variety and if soybean cyst nematodes are in the field. Early infections cause pod abortion, which reduces the number and size of seeds.

Risk factors for SDS include early planting followed by cool, wet soil in the first two to four weeks after planting; soil compaction and poor drainage; high-yield environments; high SCN populations in soil; and heavy rainfall through June to mid-July.

Resistance: Key to management

Fortunately, growers can manage SDS. First, identify the disease. Leaf symptoms of SDS and brown stem rot look similar, so know what disease you’re dealing with before making decisions.

Choose cultivars with the best available SDS resistance, Malvick says. Research shows that some resistant commercial varieties yield at least 11 bushels more per acre compared to moderately susceptible varieties where SDS is present.

Improve drainage or try deep tillage. The latter may prove helpful only in compacted areas.

You should also test for soybean cyst nematode to rule out other competitors for your plants. If you have soybean cyst nematode, plant SCN-resistant cultivars, too.

Don’t bother with crop rotation, tillage or fungides, Malvick says. None are effective on SDS.

Later in the summer, start scouting for the disease in late July through the first week of August.

Target low, poorly drained or compacted areas with your scouting, since this is where the disease often first appears. Look for yellow, diffuse spots on leaves that appear first in mid-canopy.

Looking ahead to the 2011 season, Malvick says he has no idea how far north SDS may spread.

He adds: “If we have weather like last summer, with lots of rain, I think we will see more SDS.”

Confirmed distribution of SDS in Minnesota;
37 counties with confirmed SDS,
as of November 2010.
D. Malvick, et al., University of Minnesota


This article published in the February, 2011 edition of THE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.