The increase in size of the leafspots is limited by veins, giving the lesions an angular appearance. The upper surface of the spot fades to tan, and many of the diseased spots eventually drop out, leaving irregular holes. On the lower surface of the tan lesion, a white crust is formed when the sticky, milky ooze produced by the spot dries. This crust can be used to distinguish scab-infested plants from those with angular leaf spot. On stems and fruits, the lesions have a water-soaked appearance and may also become covered with crusty white exudate.
Brown areas appear on the surface and brown streaks extend internally down to the seeds.
Downy mildew is distinguishable from angular leafspot by chlorotic margins and purple fuzz on leaf undersides where the spores form. The angular leaf spot pathogen survives on infected plant residue, volunteer seedlings, infected seed, and older plantings. It spreads through the field by any movement of people or equipment, especially when foliage is wet. Temperatures between 70 degrees and 80 degrees F enhance disease development. Disease-free seed and a 1 to 2 year rotation lower disease incidence.