White rot (Sclerotium cepivorum)Also known as allium root rot, this is fungal disease which can spread from plant to plant down a row via its mycelium of white filaments. It also forms black sclerotia, or storage structures, which can lie dormant in the soil for years until they detect chemicals exuded from allium species in the the cool, moist conditions that it requires. Leeks are generally less severely affected than onions and garlic. Warm, dry conditions will slow the spread of the disease.
- Yellow, wilting foliage which then dies
- White mould is usually visible on the base of the plants but it can spread to cover the whole bulb
- The mould is sometimes dotted with the poppy seed-sized black sclerotia
Prevention & control
- Lift and burn affected plants as soon as possible, preferably with a good spadeful of surrounding soil, but be careful not to drop potentially infected matterial on surrrounding areas
- Don't grow susceptible crops again for at least five years.