Excessive rainfall can accelerate stem canker development in soybean fields, causing devastating yield reductions of up to 90 percent. Effective field management and surveillance practices can preserve crop health.
Factors to Consider
- Weather and environmental changes
- Identification of disease
- Treatment selection
- Follow local weather conditions. During early stages of vegetative growth, extensive rainy periods increase the likelihood of infective stem canker. Humid and damp conditions with temperatures from 70 F to 95 F initiate the fungal bacteria in the soil. Fields with hail damage and reduced tillage are also at risk for stem canker development. Mortality risk increases when dry conditions follow infection.
- Identify disease in fields. Stem canker is caused by the fungus Diaporthe phaseolorum. Main symptoms include reddish-brown lesions (cankers) with dark red-purple margins on the lower stems, petioles and nodes of the plant. Watch for leaf yellowing, with green veins similar to sudden death syndrome. As the disease develops, the cankers appear along the main stem or lateral branches. Cankers prevent water and nutrient flow and prematurely kill the plant. Scout fields every two weeks from pod development through harvest maturity.
- Select appropriate treatment. A variety of methods can prevent stem canker and ensure field health. In fields with a history of stem canker, consider delaying planting until the latest opening and use conventional tilling to improve soil aeration. Some soybean cultivars are resistant to stem canker and should be considered. There is little evidence to suggest foliar-applied fungicides affect stem canker development.
- Plan future prevention. A fungus is dormant during winter months in infested crop debris and may spread to seeds. Symptoms appear at the reproductive stage when the soybean plant is under significant stress due to high reproductive demand. Research shows stem canker spreads from one region to another by means of infected seeds, contaminated equipment or windblown rain. Reduce infestation in soil with annual rotation to grass crops and fall tillage to destroy crop residue where the fungus overwinters.
Stem canker in soybeans is harmful to crops without preventive action and monitoring. Take appropriate precautions to reduce risk of this fungal disease affecting your fields. For more information, contact your local Mycogen Seeds representative or trusted agronomic adviser.