Pacific Pests, Pathogens and Weeds

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Summary

• 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.