The central portion of each spot appears slightly raised and develops into a small pustule, especially on the underside of the leaf. Several infections on the same leaf produce a large, yellow to brown area with small, dark brown spots. The brown, dead areas on older leaves may break up and cause a ragged appearance. In later stages, the pustules rupture and dry. When rupturing and drying occur, it may be difficult to distinguish this disease from bacterial blight.
Severe infections cause defoliation.
The disease overwinters in infected plant debris and is carried over to some extent on infested seed. Crop rotation, resistant varieties and burial of crop residues are the most effective methods of disease control.