Brown Spot of Soybean
The first symptoms usually appear on older leaves in the lower canopy. Warm and rainy weather during the growing season may favor its progression up the plant. Small irregular dark-brown spots develop on both surfaces of the leaves, often only on one side. As the disease progresses, the spots enlarge and coalesce into irregular brown areas embedded in yellow patches, often starting along the leaf edge or the veins. Later, whole leaves turn rusty brown and yellow, and shed prematurely. Damage is not comprehensive.
Brown spot is a leaf disease caused by the fungus Septoria glycines. It overwinters on infected plant residues and on seeds in the soil. Splashing rain scatters the spores onto the leaves. The development of the disease is favored by environmental conditions that favor continuous leaf wetness. Extended periods of warm, moist and rainy weather, and temperatures around 25°C are ideal for its growth. Symptoms develop between 15 and 30°C. However, the spread of the fungus stops during hot, dry periods.
Apply products containing Bacillus subtilis in early stages of the disease.
Always consider an integrated approach with preventive measures together with biological treatment if available. Damage caused by brown spot is usually minor. So, fungicide treatments are generally not recommended. Seed treatment with fungicides can be used preventively. In rainy years, apply fungicides of the group of azoxystrobin, chlorothalonil and pyraclostrobin on the above-ground plant parts.