Brown Stem Rot (Soybean)

Phialophora gregata

Soybean stem broken open to reveal Brown Stem Rot infection
Soybean stem broken open to reveal Brown Stem Rot infection. Photo courtesy of Daren Mueller. Licensed under CC BY 3.0.
Often confused with SDS, brown stem rot is a common disease in soybeans that is known to cause significant damage. It is most easily identified by splitting open the stem to reveal the brown, infected pith. Brown stem rot does not generally pose a problem for the southern part of the U.S. since it needs cooler weather (60-90 degrees F) during early pod development.
BSR is a soilborne fungus that usually doesn't become actively apparent until August. Optimal temperatures for development are between 59 and 81 degrees F. After the temperature rises above 90 degrees F, the disease is halted. It can be hosted by the soil or infected crop residue. The fungus infects the soybean plant through the root system early on in the growing season, often not appearing until cool, wet weather is followed by hot, dry weather.
Symptoms of BSR are easily confused with that of SDS and are usually worsened by the presence of soybean cyst nematode. The main, easily identifiable symptom is the browning of the pith in the main stem of the soybean plant. The height of the discolored pith is an indicator of the severity of the infection. Less severe cases have browing only at the nodes, while severe cases have continuous discoloration from the base upwards. In certain cases, leaves adopt a brown or yellow discoloration between the leaf veins similar to SDS. The discoloration is followed by curling, wilting, and ultimately death of the leaf. The only true way to tell the difference between BSR and SDS is by looking at the pith discoloration, which is symptomatic only of BSR.
Yield losses have been reported as high as 30 or 40 percent, and it is known to be most severe in high-yield areas. Yield loss occurs through the premature death of plants. Plant damage is done through the release of toxins by the fungus inside the plant. Severity depends on environmental conditions, the variety of soybeans affected, and the acutal strain of fungus inside the plants.
Planting later in the spring can be a good way to reduce the risk of brown stem rot, but it holds the potential to reduce overall yields. Conventional tillage practices are encouraged for continual soybean fields, but in the case of intermittent tillage with rotated crops, risk of BSR may also be reduced.
Neither foliar nor seed treatment fungicides have proven to be effective in BSR control. Research has indicated that maintaining a constant pH of 7 will reduce the chances of BSR infection. 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.
There are some available varieties of resistant soybeans. In the case that high brown stem rot pressure (BSR) is expected in a field, resistant varieties of soybeans should be planted. It is recommended that varieties resistant to suddent death syndrom (SDS) and soybean cyst nematode (SCN) be considered first. Following severe infestations of BSR, rotating away from soybeans for at least 2 years is very highly recommended.