It occurs on white onion varieties and reduces the market value of the bulbs. The disease is characterized by small dark green to black spots, which appear on the outer scales.

Blemishing dots on outer the outer bulb scales of onion. On, over the surface of the bulb, masses of minute stromata form beneath the cuticle.

On the outer bulb scales, over the surface of the bulb, masses of minute stromata form beneath the cuticle. These bodies, dark green at first, blackening with age, are sometimes scattered over the surface of the bulb but are more frequently concentrated in smudge-like spots, roughly circular, or arranged in concentric rings 1-2 cm diameter or more.