Botrytis neck rot usually becomes obvious after harvest, although infection can begin while onions are still in the garden. The fungus enters the neck and gradually spreads into the bulb. The neck becomes soft and the affected scales turn greyish-brown. Grey mold may develop between the scales, followed by small, hard black structures called sclerotia. Eventually, much of the bulb can rot.

How to Fix It

There is no way to cure an onion once the bulb is rotting.

Remove and discard affected bulbs so they do not spread the disease in storage. 

Harvest onions in dry weather when possible and avoid bruising or damaging the bulbs.

Cure onions thoroughly before storing them—the neck should be completely dry and tight. 

Store only sound, well-cured bulbs in a cool, dry, well-ventilated place. Remove onion debris and cull bulbs from the garden and rotate onions and related crops to reduce carryover of the fungus.