Neck rot: Fungus development in onion bulb
Pathogen: Botrytis allii
Symptoms
Small black sclerotia may develop on the outer scales around the neck. 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.
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 promotedisease development and spread.
Disease Management
Use varieties that are adapted to the growing area to ensure that the plants mature by harvest. 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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