Causal Agent
Streptomyces scabies
Distribution
Worldwide
Symptoms
This disease is most commonly on radishes, but also infects turnips and rutabaga. As the root swells, small (1mm; 1/32 in.) white lesions develop on the root surface. A ridge of light-colored tissue forms at the margin, while the center of the lesion darkens, giving it a crater-like appearance. Secondary infections of lesions by other organisms may cause discoloration and softening of the root.
Conditions for Disease Development
The bacterium survives host-free for many years in alkaline to neutral soils. Dry soil and poorly fertilized soils favor disease development.
Control
Implement long crop rotations to non-hosts. Eradicate fleshy, rooted weeds, such as pigweed (Amaranthus sp.). Avoid the use of soil amendments that increase soil pH. Apply acid-producing fertilizers. Irrigate during periods of warm, dry weather to help reduce infection.
Australia / New Zealand