Scout for Cercospora leaf blight starting at the beginning of the reproductive growth stages. Look for a purplish-bronze discoloration on the upper surface of leaves, particularly in the upper canopy where leaves are exposed to sunlight. As the plants mature, the leaves begin to look leathery. In susceptible cultivars, the entire leaf surface may have this appearance. If you look closely at individual leaves, you can see reddish-purple spots that vary in size from pinpoint spots to larger, irregularly shaped patches. Severely affected upper leaves are often shed while lower leaves remain attached.

Cercospora leaf blight is most commonly mistaken for sunburn

At maturity, check the seed for purple discoloration. If the fungus infects the seed, symptoms can range from no symptoms, to a purple discoloration that can cover part or all of the seed. The seed phase of the disease is commonly called purple seed stain.

Be aware that there is little correlation between symptom development on the leaves and on the seed.