Late Season Soybean Stem Diseases

As a result of seeing several late-season stem diseases, Sam Markell, Extension Plant Pathologist has republished the following article in the Sept. issue of the NDSU Extension Service Crop and Pest Report.

We are seeing several late-season stem diseases show up in North Dakota; notably, brown stem rot and charcoal rot. Now is a great time to examine your soybeans for diseases; particularly stem disease whose symptoms appear late in the season; brown stem rot, charcoal rot and sudden death syndrome which is not yet found in North Dakota. To maximize your ability to check for soybean diseases bring a knife, and if needed, a magnifying glass.

Brown Stem Rot (BSR)

BSR has been found in multiple locations in ND. Symptoms and signs begin to occur in mid-August. Leaf symptoms may or may not occur, and are not particularly diagnostic. Leaf symptoms of BSR rot include a yellowing (chlorotic) and browning (necrotic) between the leaf veins Stem symptoms are much more important. To check plants for brown stem rot take a knife and slice the lower stem longitudinally. Brown stem rot will cause a browning of the center of the stem. Plants with BSR have 'lead in a pencil look'; only the center of the stem is dark.

Charcoal Rot

Charcoal rot is caused by a pathogen that can infect soybeans, corn, and sunflowers. Symptoms of the disease don't generally appear until the reproductive stages of growth, and the disease is more common when the latter half of summer is dry.

Field-wide symptoms appear as patches of plants that matured quicker than healthy plants, resulting in prematurely dead soybeans. The top leaves may turn brown and premature leaf drop will occur.

Stem symptoms. The roots and lower stem of plants with charcoal rot may appear gray. Scrape or shave off the outer tissue of the lower stem with a knife. Infected plants will be covered with black microsclerotia, giving the appearance of being dipped in charcoal dust. Microsclerotia can be observed with a magnifying glass, but they are very small.

Sudden Death Syndrome (SDS)

SDS has not yet been confirmed in ND, but it has been found in Ottertail County, MN. SDS is not usually observed until early August, it is typically associated with soybean cyst nematode, and when the two act together significant yield loss can occur.

Foliar symptoms of the SDS include chlorosis and necrosis between the leaf veins. Unlike BSR, these foliar symptoms consistently occur when plants are infected with SDS.

Stem symptoms. Take a knife and longitudinally slice open the lower stem and root ball. With SDS, the center of the stem remains white, but a light brown discoloration may occur on the outer stem tissue.

For more information please visit http://www.soybeanresearchinfo.com or http://www.extension.umn.edu/agriculture/crop-diseases/soybean.