Background:

Septoria brown spot is caused by the fungus Septoria glycines. This disease is the most common foliar disease in soybeans. Septoria brown spot develops soon after planting as it’s usually present throughout the growing season. It infects the lowest leaves in the canopy. After following a rainy season, the disease can move throughout the plant. As the septoria brown spot develops and grows, infected leaves usually turn yellow and drop prematurely. Soybean plants weakened by other diseases become more susceptible to brown spot. (Crop Protection Network Septoria Brown Spot)

Scouting:

The symptoms for this disease include several small, irregular, dark brown spots on the leaves. The spots frequently merge to form irregularly brown blotches, especially along leaf edges or leaf veins. Brown spot begins on the oldest leaves and turns entire leaves yellow. They then drop from the plant.

Management: