Soybean
Stem Blight of Soybean
Diaporthe phaseolorum var. sojae
Fungus
In a Nutshell
- Linear rows of dark specks on stems, petioles, and pods.
- Reduced seed quality.
- White chalky mould on the seed surface.
Can also be found in
Soybean
Symptoms
The most noticeable symptom of stem blight is the presence of pycnidia (fungal fruiting bodies), which are small, black raised dots arranged in rows on infected stems, pods, and fallen petioles late in the season. Upper portions of the infected plants may turn yellow and die. Seeds affected by Stem Blight are often cracked, shriveled and dull and may be covered by gray mould. Infected plant parts might die prematurely.
Recommendations
Organic Control
There is no effective biological control method available for this disease. If you know of any successful method to reduce the incidence or the severity of the symptoms, please contact us.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments, if available. Foliar fungicides can protect the quality of seeds if applied near the beginning of seed formation. Fungicides applied from pod set through late pod stages will lower seed infection incidence. Infected seeds should be treated before sowing.
What caused it?
Stem blight is caused by the fungal species of Diaporthe phaseolorum, often also referred to as Phomopsis sojae. The fungi survive in both infected seeds and crop residues during winter. Infected seeds will be shrivelled, cracked and covered with white mycelium. Severely infected seed may not germinate. Prolonged periods of warm, wet weather during pod development and maturation favour the spread of the disease from the pod to the seeds. Very wet conditions favour stem infections during pod filling stages. The pathogen can cause significant yield losses and reduces seed quality.
Preventive Measures
- Use high quality and disease-free seeds for planting.
- Avoid planting soybean on a field that was previously affected by stem blight.
- Examine plants every two weeks from pod fill to harvest maturity stage for the presence of stem blight.
- Keep your field free from alternative host weeds such as velvetleaf and pigweed.
- Delaying harvest increases the risk of stem blight because plants are likely to be exposed to cool and wet conditions that favour disease development.
- Harvesting on time and doing proper tillage can reduce the amount of inoculum.
- Practice crop rotation with non-host crops such as corn or wheat.
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