Worldwide distribution. On onion, leek, Welsh onion (Japanese bunching onion), Chinese chive, shallot. A cosmetic disease.
On the lower parts of the outer leaves and neck, in patches or rings.
Spore masses with long stiff hairs. Spots on leaves turn to blights under wet warm conditions.
More serious rots occur if onions harvested wet and stored moist >20°C.
Causes a seedling damping-off.
Spread occurs in wind-driven rain.
Cultural control: well-drained soil; clean seed and healthy transplants; avoid harvesting in wet weather; cure bulbs quickly and store cool and dry; plant those with coloured outer scales; 2-3-year crop rotations.
Chemical control: possibly, mancozeb, or chlorthalonil.