|Cross section of an onion bulb showing neck rot symptoms|
|Species:||Botrytis allii, Botrytis cinerea and Botrytis squamosa|
|Botrytis leaf blight (B. squamosa)|
Neck rot is a Botrytis infection of alliums caused mainly by B. allii, but also B. squamosa and B. cinerea. It is the most common infection of onion bulbs rotting in store in temperate climates.
Susceptibility differs with variety; white varieties are especially susceptible, but red and yellow varieties may also sustain heavy losses. Symptoms usually appear when after harvest, but infection occurs while crop is still in the field. Greatest epidemic conditions are when cool (10-21°C (50-70°F)), moist weather prevails for several days during harvest.
Symptoms are first seen as a softening around the neck of the bulb. In a humid atmosphere a grey mould appears around the softening site. Sclerotia may be found under the skin as small grey/black bodies.
None. Examine stored bulbs regularly and remove and destroy rotten bulbs immediately.
Grow varieties that are known to store well, and follow production practices that promote crop storability. Good storage onions have at least three wrapper scales, and the neck will tighten when dried. Avoid excessive and late (after mid-July) applications of nitrogen. Do not irrigate within 10 to 14 days of lifting onions. Allow tops to dry approximately 1 week before topping. Harvest only when the crop is mature, and during dry weather. Provide good ventilation for curing onions before storage.
A preventive fungicide spray schedule is the primary means that commercial growers use to suppress development of Botrytis leaf blight. Destruction of cull piles, deep soil turning, and long rotations are also recommended to reduce losses to this disease.
Potential hosts of neck rot:
- Hessayon, D.G. (2009). The Vegetable & Herb Expert. Transworld Publishers, London. p. 75. ISBN 9780903505468
- Johnson, Dennis A. (1996). Botrytis Neck Rot of Onion. Washington State University Irrigated Agriculture Research and Extension Center, Prosser. Retrieved 2010-07-21.
- (2003). Crop Profile for Onions in Georgia "Botrytis Leaf Blight". National Information System for the Regional IPM Centres. Retrieved: 2010-10-22.