Brown stain of dried outer scales. Improperly disposed onion culls. Downy mildew symptoms. Neck rot symptoms are most characteristic of botrytis and often appear after bulbs are stored for two weeks or more. The fungus grows down through the inner scales and may partially rot the bulb before external injury appears.
Infected scales become soft, brownish and spongy.
Gray mold or thin and irregularly-shaped black sclerotia may form between scales or, more commonly, at the neck area. The neck area becomes sunken and the entire bulb can become dried out. Secondary invasion by soft rot bacteria may cause a watery rot. Proper sanitation of onion debris, especially culled onions, is very important. Incorporate this material into the soil immediately after harvest.