Q How do I recognise neck rot in onions?
A Neck rot, caused by the fungus Botrytis allii, is largely restricted to onions. The damage starts around the neck of the bulb, causing the scales to become pale brown and semi-transparent. A dense, greyish fungal growth then develops around the neck. Black fungal resting bodies (sclerotia) form and, if the onions have not already been lifted, they fall into the soil and may cause other onions to become infected. Neck rot is also spread by spores. Symptoms develop more rapidly in store, and this may be where they're first noticed.
Caption: Use any onions affected by neck rot as soon as you can
Q What can I do if my onions have neck rot?
A There's nothing you can do to help affected onions. Use them in the kitchen as quickly as possible.
Q How can I prevent onion neck rot?
A Don't grow onions on the same site for more than two years in succession. Ideally, rotate crops each year. Avoid excessive use of high-nitrogen feeds and do not feed at all after mid-summer as this will encourage neck rot. Keep onions dry when they are drying off.