Neck rot: External symptom with fungal growth
Pathogen: Botrytis allii
Symptoms
A dense grey mould growth develops, producing huge numbers of spores. Masses small black sclerotia grow on the outer scales around the neck. Affected internal parts of the bulb are brown, water-soaked and spongy.
Disease Development
Disease spread is most rapid during moderate temperatures with high humidity, rainfall or overhead irrigation. Infection can be more severe if necks are still succulent when stored. Storing uncured onions at temperatures and humidity which are too high can promote disease development and spread.
Disease Management
Avoid excessive late season fertilizing, which may delay maturity. Adjust plant spacing and row orientation to obtain the best air movement through the plants. Avoid injury to the onion neck and damage to the bulbs, especially at harvest. Field applications of fungicides prior to harvest may reduce disease severity. Destroy onion cull and debris piles that may serve as a source of inoculum. Deep plow fields with a history of the disease to bury the sclerotia and rotate out of onions in these fields for several years. Be sure bulbs are cured and remove damaged bulbs before storage. Do not allow moisture condensation to form on the bulbs and use cool temperatures and moderate humidity for bulb storage.
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