Join the RHS today and support our charitable work
Keep track of your plants with reminders & care tips – all to help you grow successfully
RHS members get reduced ticket prices
RHS members get free access to RHS Gardens
Free entry to RHS members at selected times »
Reduced prices on RHS Garden courses and workshops
020 3176 5800
Mon – Fri | 9am – 5pm
Help us achieve our goals
Join the RHS today and support our charity
This fungal disease develops during storage, and can cause severe losses of onion and shallot bulbs. Prevention of neck rot depends on the use of appropriate cultural techniques, particularly in relation to conditions at harvest and during storage.
Onion neck rot
Onion neck rot is a disease of onions and shallots caused by the fungus Botrytis allii. Plants infected by the fungus usually appear perfectly healthy whilst the crop is growing. Symptoms are not usually seen on the bulbs until they have been in store for several weeks. In general, onion cultivars with white bulbs are more likely to be attacked than those which have red or yellow bulbs.
You may see the following symptoms:
There are no fungicides available to gardeners for the control of onion neck rot. However, several seed companies now treat their seed to reduce infection.
The neck rot fungus can contaminate both seed and sets, and also persists in the soil on debris and as sclerotia (resting bodies). Plants grown from contaminated seed are infected almost as soon as the seed germinates. Spores produced on the affected plants can spread the fungus through the crop, but infected plants usually remain symptomless during the growth of the crop.
The bases of the older leaves eventually become infected, and the fungus spreads from here into the neck of the bulb. High levels of neck rot developing in store are often the result of factors during growth, harvesting and storage that favour the pathogen. These include:
Allium leaf minerLeek mothLeek rustOnion downy mildewOnion flyOnion white rotOnions and shallots
the RHS today and get 12 months for the price of 9
RHS members can get exclusive individual advice from the RHS Gardening Advice team.
We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.