Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

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Onion black mould (187)

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Photo 1. Black mould, Aspergillus niger, along the veins of an onion bulb.

Photo 2. Black mould, Aspergillus niger, on onion. The bulb on the left is showing large spore masses, whereas the mild infection on the right is mostly along the veins.

Photo 3. Black mould, Aspergillus niger, on garlic clove.

Summary

• Worldwide distribution. On seeds, bulbs, tubers, fruits and flowers of coconuts, maize, onion, peanuts, rice, and sorghum, and many other hosts. A cosmetic problem.
• A fungus, usually on organic matter in soil, attacks stored fruits, seeds, roots/tubers, if they are wounded. On onions, it infects dying leaves in the field after harvest; from there  the bulbs become infected, often along the veins. It also infects onions when “topped” before storage, especially in hot, wet weather.
• Spread occurs as spores in the wind. The fungus is seed borne.
• Cultural control: well-drained land; ensure seed is clean, or treat in hot water (60°C for 15 min.); dry bulbs after harvest, before storage; varietal resistance (those with red scale leaves); collect trash and burn after harvest.
• Chemical control: seed treatment: mancozeb or thiram.

Common Name

Black mould, collar rot, neck rot

Scientific Name

Aspergillus niger

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