The Cause of Brown Stem Rot

Brown stem rot (BSR) is a fungal disease that affects soybean plants and is caused by the pathogen Cadophora gregata. This disease poses a significant threat to soybeans by targeting the plant’s vascular system and disrupting efficient water and nutrient transport. This can lead to wilting, plant stress and less vigor.

BSR symptoms typically become evident during the reproductive stages of plant growth. They show up as interveinal chlorosis (yellowing between leaf veins) and leaf necrosis (tissue death). 

Symptoms

In soybeans, brown stem rot (BSR) can exhibit a range of symptoms. Here are the key signs to look for:

Leaf symptoms: Interveinal chlorosis can mimic nutrient deficiency symptoms. Leaf necrosis occurs as the tissue between veins turns brown and withers, creating a scorched appearance.

Stem symptoms: With BSR, the lower stem displays a distinctive brown discoloration, beginning at the base and extending upwards. This coloring varies, spanning light brown to a pronounced dark brown or even reddish-brown shade. Additionally, a clear line of separation might emerge between healthy and infected stem tissue. This division becomes particularly apparent when the stem is split open.

Pith discoloration: The pith, which is the central tissue of the stem, becomes discolored and brown. Healthy plants should have a white pith.

Vascular tissue impact: The vascular tissues within the stem, responsible for transporting water and nutrients, can be damaged. This can cause plant stress and wilting.

Pod and seed symptoms: Infected plants may produce fewer and smaller pods compared to healthy plants. Seeds within infected pods can be smaller, discolored and may have reduced quality.

Late-season symptoms: Symptoms tend to become more evident as the plant reaches reproductive stages. So signs of BSR will usually become more pronounced later in the growing season.

It’s important to note the severity of symptoms can vary depending on the soybean variety, the presence of the pathogen in the soil, environmental conditions and overall plant health. 

Other soybean diseases can exhibit similar symptoms, so accurate diagnosis may require assistance from agricultural experts or diagnostic laboratories.

To effectively manage brown stem rot, early detection and accurate identification are crucial. If there are potential BSR symptoms in your soybean fields, consider seeking advice from local AgriGold agronomists who can provide proper diagnosis and management recommendations.

Factors Influencing Brown Stem Rot

Several elements can contribute to brown stem rot development—and severity:

Soilborne pathogen: The presence of the fungus in the soil is the primary factor leading to BSR development.

Environmental conditions: Cool, wet conditions during the growing season, especially at the reproductive stages, can favor BSR. The disease is often more severe in regions with a history of the disease and in fields with poor drainage.

Crop rotation and tillage: The pathogen can survive in crop residue and infected roots. So, BSR is more likely to develop in fields with continuous soybean cropping and/or reduced-tillage practices.

Soybean varieties: Some soybean varieties are more susceptible to BSR than others. Planting resistant or tolerant varieties can help mitigate the disease’s impact.

Management Strategies

Managing BSR in soybeans involves a combination of cultural practices, preventive measures and, when necessary, chemical control methods. Here are some strategies to effectively tackle BSR:

Appropriate varieties: Choose soybean varieties that are resistant or tolerant to BSR. Resistant varieties have genetic traits that can help minimize the disease’s impact.

Crop rotation: Rotate soybeans with non-host crops such as corn or small grains to break the disease cycle. Continuous soybean cropping can increase pathogen buildup in the soil.

Seed treatment: Use fungicide-treated seeds to protect young plants from early infection during the vulnerable early growth stages.

Good drainage: Improve field drainage to reduce the likelihood of infection during wet conditions. Well-drained fields can help prevent the pathogen’s spread through the soil.

Avoid excessive nitrogen: High nitrogen levels can exacerbate the disease’s impact. Balanced nutrient management can help reduce symptom severity.

Sanitation: Remove and destroy infected crop residue after harvest. This reduces the amount of inoculum that can survive in the field.

Planting date: Opt for planting dates that reduce the risk of prolonged exposure to cool and wet conditions.

Foliar fungicides: In fields with a history of the disease or that are under conditions conducive to BSR, consider foliar fungicides. Consult with agricultural experts to determine appropriate timing and product selection.

Integrated Pest Management (IPM): Incorporate BSR management into your overall Integrated Pest Management plan. This includes a combination of practices tailored to your specific field conditions.

Soil testing: Regularly monitor pathogen presence in your soil through testing. This can help you gauge the risk of BSR and make informed management decisions.

Use resistant cover crops: If you practice cover cropping, plant BSR-resistant crops to help reduce pathogen buildup during the offseason.

Consult AgriGold: If you suspect BSR in your fields, seek advice from an AgriGold agronomist, extension service member or plant pathologist. Proper diagnosis can guide effective management strategies and limit negative impact on your yields.

The Bottom Line

• Early recognition is important. Promptly identifying BSR symptoms like chlorosis, necrosis and stem discoloration during soybean reproductive stages can mitigate the disease’s impact.
• Implement proactive farming practices, like better drainage, strategic planting dates and resistant soybean varieties. These can all help reduce BSR-friendly conditions and enhance crop protection.
• Invest in knowledge. Stay informed about the latest BSR management techniques. Consult experts for guidance to safeguard your soybean investment and ensure continued crop health and productivity.