When it comes to soybean diseases, early detection and treatment are key. Here are a few early season soybean diseases, advice on how to spot them, and strategies for reducing your susceptibility and maintaining your yields:
Bacterial Leaf Blight
What causes it: The bacteria Pseudomonas savastanoi, plus wind and splashing water that move it from plant residue onto leaves. Bacteria then enter the plant from stomata or wounds. Windy rainstorms leading to cool, wet weather (70-80 F) are favorable conditions for this bacteria. With windy weather, infected leaves can also rub against healthy ones, spreading the disease.
When it shows up: As early as V1, but we usually see this disease in late May or early June.
How to recognize it: Lesions first appear as small yellow spots that turn a dark red/brown with yellowish green “halos,” which eventually fall out of the leaf to make the plant look ragged.
Tips to reduce susceptibility: This usually isn’t considered a yield-limiting disease. But if your fields have historically had problems with bacterial leaf blight, you should consider managing crop residue through tillage or rotation. Some seed varieties may also offer more resistance.
Septoria Brown Spot
What causes it: The fungus Septoria glycines, plus extended periods of wet, warm weather. Minimum tillage and/or continuous soybean planting on the same acres can also lead to more disease spreading (the pathogen survives on plant residue).
When it shows up: As early as V1, but it’s most common to find Septoria Brown Spot in late May or early June.
How to recognize it: Small dark brown spots on lower leaves, which can progress upward throughout the summer. They can expand and grow together into larger brown areas, often accompanied by yellow patches that diminish photosynthesis.
Tips to reduce susceptibility: Consider rotating your soybeans with other non-legume crops, and incorporate more tillage. Both foliar fungicides and selecting a more tolerant seed variety can also help you keep septoria brown spot under control.
If you’re looking for more tools to defend against these diseases, ask your local AgriGold agronomy expert which varieties could offer the most resistance.
Giesler, Loren J. Bacterial Blight. https://cropwatch.unl.edu/plantdisease/soybean/bacterial-blight
Malvick, Dean. 2018. Septoria Brown Spot https://extension.umn.edu/pest-management/septoria-brown-spot