Thanks for tuning in to our weekly “Ask the Agronomist” Audiocast! Play the audio file below to listen to Mark’s response to this week’s question about how to determine whether a soybean crop is affected by Brown Stem Rot or Sudden Death Syndrome.
Q: I thought my field was showing signs of Sudden Death Syndrome. Now I’m not sure if it’s really SDS or Brown Stem Rot. How can I tell the difference?
A: Late-season crop scouting is so important because we see different symptoms, depending on the point we’ve reached in the growing season as well as environmental conditions. We’re seeing both SDS and BSR, sometimes even in the same field!
The best way to tell to the difference is to split the soybean stem. Brown Stem Rot (BSR) infection causes vascular and pith tissues to turn brown to reddish brown. When disease is severe, discoloration is continuous from the base of the plant up. Discoloration only occurs at nodes disease when the disease is less severe, and you’ll see healthy, white tissue between the nodes.
Q: What causes Brown Stem Rot?
A: BSR is caused by a fungus that enters through the plant’s root system. Severe infestation occurs when soil moisture is high and air temperatures are cooler throughout the summer, which promotes the growth of the fungus in the stems. Symptoms worsen if the disease development is followed by drought stress during pod fill. BSR also increases in severity if Soybean Cyst Nematode populations are high.
Q: How does Brown Stem Rot spread?
A: Brown Stem Rot is a soil-borne pathogen. It survives in infected soybean residue left on the soil surface. The fungus is not carried with seed.
Q: What can be done if you find Brown Stem Rot in your fields now?
A: Unfortunately, just like Sudden Death Syndrome, nothing can be done for a field once it has been infected with BSR. Scouting now for Brown Stem Rot is important for two main reasons: (1) To determine if management practices may have had an impact on the severity this season; and (2) To select soybean seed for the following season based on BSR score and Soybean Cyst Nematode tolerance.
Q: What management practices can help control Brown Stem Rot?
A: The most effective way to manage Brown Stem Rot, Soybean Cyst Nematode and Sudden Death Syndrome is through seed selection. Latham® brand soybean varieties with the IRONCLADTM designation offer the best control, but be sure to read disease ratings of each product. For fields with a history of severe brown stem rot problems, plant a variety with a rating of 1.5 or better. A Latham rep also can help you select the best product on a field-by-field basis.
In addition, crop rotation can help reduce the likelihood of Brown Stem Rot. Going away from soybeans for 2 years is more effective than 1 year. Reducing soybean residue helps because then the BSR inoculum doesn’t have a place to overwinter. Tillage can also be effective.