The infection can occur at any growth stage but it is more common on young leaves at flowering time. Initial symptoms appear as small, brown water-soaked spots. Over time, they grow into large (1-5 mm) roundish spots with grey centers and dark purple margins. In the case of a heavy infection, leaves die and fall off. Elongated spots with crushed centers start to appear on stems. On pods, circular or elongated sunken brown spots appear. Infected seeds are shriveled and show brown spots of different sizes.
Frogeye leaf spot is caused by the fungus Cercospora sojina. It survives between plantings on crop residues in the field or on seeds. If planted, infected seeds may give rise to infected seedlings. Young soybean leaves are more susceptible than older ones. Warm, humid, cloudy weather with frequent rain favors the development of the disease. Residues of infested soybean plants left on the soil surface are favorable, too.
If available, always consider an integrated approach with biological prodcuts.
Always consider an integrated approach with preventive measures together with biological treatments if available. Two applications of products containing pyraclostrobin starting at the time of occurrence and later during the growing season can help contain the spread of the pathogen. Humid conditions enhance the effect of the fungicide. The treatment should not be started if there are less than 21 days to harvest.