Sudden Death Syndrome

SDS

Fusarium virguliforme

Soybean leaf showing symptoms of Sudden Death Syndrome
Soybean leaf showing symptoms of Sudden Death Syndrome likely having affected the entire plant. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
SDS is a soybean disease caused by a soil-dwelling fungus that inhabits fields throughout the Midwest and rapidly kills infected plants. It has been known to cause up to 100 percent yield loss.
SDS is caused by a soil-dwelling fungus that prefers cool, moist, and compact ground. It is most severe in the presence of Soybean Cyst Nematodes (SCN), during heavy midsummer rains, or when soybeans are planted in early spring while the soil is cool and wet. It tends to infect plants early on through the roots, but effects of it begin later on in the season.
Symptoms usually occur in midsummer and begin with crinkling of the leaf, followed by yellow streaks forming between the leaf veins. Soon the whole leaf turns brown and in some cases drops, leaving the petiole still attached to the stem. In diseases or chemical burn causing similar foliar symptoms, SDS is easily recognized by the fact that the leaf itself detaches from the petiole, rather than the petiole and leaf both detaching from the stem as a unit. If the stem is cut open, it will reveal a white pith surrounded by tan to light brown streaks in the cortex. No other stem disease has a white pith with the same level of cortex discoloration as SDS. The roots, which are the epicenter of the infection, will be lacking in vigor and probably rotted. Some roots will have blue patches covering the exterior, depending on the moisture level of the soil.
Soybean Root Affected by SDS
Soybean root affected by SDS infection. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
SDS is one of the most dangerous diseases to soybeans in North America, second only to SCN. When the soil becomes wet, the fungus produces a toxin that spreads throughout the plant, causing the foliar symptoms. The fungus itself causes rotting of the root system. Yield losses of up to 100 percent have been recorded. It does not spread rapidly on its own, but it can be spread rather quickly with the assistance of water runnoff.
Due to the tendency of wet, compact soils to favor the disease, tillage can be a very important aspect of SDS prevention. In most cases it breaks up the soil, making drainage more prevalent. Tiling a field in order to further improve drainage can prove to be a helpful prevention strategy. The underlying principle is that a well-drained field will have lower risk of SDS infection. Planting soybeans later in the spring when the soil is warmer will give emerging seedlings a better chance of fending off infection. Be sure to map affected areas on a GPS-enabled device, keeping track of certain problem areas, and plant all non-infected areas before these.
Seed treatment or fungicides applied during planting season will have a limited effect on SDS, while foliar fungicide will have no effect against the fungus. Mechanical and cultural management are much more effective options for prevention and control. Please contact your local plant pathologist to learn what is most effective in your area and how to use it best. Always read and follow all label instructions.
Developing a highly-resistant soybean has proved difficult, but most available varieties have some resistance to SDS. Rotating cover crops and corn has not proved to be an effective strategy in reducing the presence of SDS, even after multiple years without soybeans.