Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

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Onion smudge (186)

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Photo 1. Spots over an onion bulb caused by smudge, Colletotrichum circinans.

Photo 2. Onion smudge, Colletotrichun circinans, in diffuse patches at the base of the bulb.

Photo 3. Stiff long hairs within the spore masses of the smudge fungus, Colletotrichum circinans;  they can be seen with a hand lens.

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.

Common Name

Smudge of onion bulbs, anthracnose of onions

Scientific Name

Colletotrichum circinans

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