Symptoms and Signs
Plants affected by basal rot show progressive yellowing and dieback from the tips of leaves. Affected roots are dark brown to dark pink. A white fungal growth is sometimes evident at the base of infected bulbs. When an infected bulb is cut vertically, a brown discoloration of the stem plate tissue is apparent. Later, the stem plate tissue becomes pitted and shows a dry rot. Under dry conditions, the stem plate and dry outer scales crack open. Basal rot can continue in storage.
Comments on the Disease
The fungus survives indefinitely in soil. Infection occurs through wounds or in the vicinity of old root scars at the base of the bulb. The disease is favored by soil temperatures in the range of 57° to 90°F, with optimum temperatures being 79° to 82°F. Basal rot is more prevalent in transplanted onions than in direct-seeded onions.
Avoid fields with a history of basal rot problems and rotate 3 to 4 years out of onions, garlic, and leeks. Control soil insects and foliage diseases. Cure onions properly before storage. Store at cool temperatures since infection is favored by warm conditions.