The lesions then develop into bright yellow spermogonial (conceptacle containing spermatia) pustules, usually on the upper leaf surfaces of the host plant. Spermogonial pustules may also appear on any of the above-ground plant parts, such as the stems. Within about 10 days of spermogonium formation, cup-like aecia (spore reproductive structures) erupt through the lower leaf epidermis.
As lesions progress, they transform into bright yellow pustules containing spermatia on the upper surfaces of host plant leaves and sometimes on stems. About 10 days after spermogonium development, cup-like aecia (spore reproductive structures) burst through the lower leaf surface.