Pathogen(s) causing disease:

Cercospora kukuchii

Symptoms:

Easy to identify because of the mottled purple-to-orange discoloration of the uppermost leaves and leathery leaf appearance. In September, when soybean plants are approaching maturity, infected leaves turn orange or bronze.

Conditions:

Late season disease is often mistaken for early senescence. Symptoms are first observed at the beginning of seed set. This fungus survives on the seed coat or on crop residue. Spores from infected seed cotyledons are splashed or wind-borne to leaves and stems.

Management:

Tillage and crop rotation are effective ways to reduce the survival of these fungi from season to season on infested soybean residues. Rapid decay of infested residue prevents a build-up of the pathogen and potentially greater infection in the next soybean crop.

Sources:

NC State
ISU
U of MN