Neck rot

Botrytis allii

Decay of bulbs from the neck downwards, with copious grey mould and hard, black resting bodies. 

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:
Bulbs are usually first affected at the neck, although the decay can spread downwards to affect the whole bulb. Occasionally, symptoms develop at the side or the base of the bulb if there has been physical
damage at this point
Scales of diseased bulbs become soft and brown, giving them a ‘cooked’ appearance
A dense grey mould growth develops, producing huge numbers of spores
This is often accompanied by hard, black, crust-like structures (the resting bodies or sclerotia of the fungus)
Affected tissues gradually dry up so that the bulb suffers from a dry rot and eventually becomes sunken and mummified

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