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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.
Common name Onion neck rotScientific name Botrytis alliiPlants affected Onions and shallots (occasionally garlic)Main symptoms Decay of bulbs from the neck downwards, with copious grey mould and hard, black resting bodiesCaused by FungusTiming Symptoms appear during storage. Infection occurs during growth and harvesting of the crop
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 white rotOnions and shallots
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