Cause Streptomyces scabies (syn: Streptomyces scabiei), a filamentous bacterium that lives in soil and can infect storage root and tuber portions of beets, potatoes, parsnips, carrots, radish, and potentially other root and tuber crops. Neutral or alkaline soils favor common scab development, it survives a short period of time in acidic soils. Soils containing high levels of organic matter which is not fully-decomposed, can have more severe disease.
Symptoms Corky lesions appear on the storage root's surface. Lesions may be small and superficial or consist of deep pits.
Cultural control
- Do not plant in fields with a history of severe disease.
- Do not plant carrots following potato crops.
- Incorporate post-harvest practices to encourage the breakdown of plant residues of root and tuber crops to decrease the soilborne survival of S. scabies.
- Use tolerant varieties if available.
- Lower the soil pH if above 7.0 or greater.
- High soil moisture for 1 week before emergence and 8 weeks after reduced common scab in 'Russet Burbank' potatoes. High moisture is defined as 80% or above of available moisture, measured at 9 inches in the soil.
- On calcareous soils, postplant sidedress applications of triple-superphosphate suppressed common scab in potato, even when soil phosphate levels were greater than 20 ppm.
Biological control
- Bexfond at 7 to 14 fl oz/A. O