Cause Aphanomyces raphani, a fungus-like organism. The disease has been so severe in northwestern Oregon fields that the crop has been plowed under. The variety White Icicle is very susceptible. The fungus attacks primarily radish but also can infect many other crucifers.
Symptoms Symptoms appear around side roots, or at growth cracks, or at wounds on the upper root. These areas are discolored a brown to bluish black. As the disease progresses, root growth there ceases, resulting in a blackened, constricted area that sometimes girdles the entire root. This black discoloration extends inward in radial streaks.
- Plant in a well-drained area and avoid overwatering.
- Use a 3- to 4-year crop rotation.
- Variety 'White Spike' is less susceptible than 'White Icicle', and 'Red Prince' has more resistance than most other red globe types. 'Fuego' and 'Belle Glade' also are resistant.