Common Scab

Common scab produces raised, rough, corky lesions on the tuber or root surface. Depending on the strain present and local conditions, lesions can be shallow and superficial or deeper and pitted. Internal tissue is generally unaffected, so the disease is mainly a cosmetic and marketability concern rather than a threat to plant survival.

Pathogenic Streptomyces survive readily in soil, particularly where organic matter is present, and infect young, expanding tuber or root tissue through lenticels or wounds during a relatively narrow susceptible window early in development. Once the tuber or root surface matures, susceptibility declines sharply.

Soil survival

Pathogenic strains persist in soil organic matter, providing inoculum across seasons

Narrow infection window

Infection is concentrated in the early period of tuber or root expansion

Moisture and pH sensitivity

Dry soil and higher soil pH during this window favour disease development

Potato is the most economically significant host of common scab. Radish and beetroot are also affected, along with other root and tuber crops in some regions.

• Dry soil conditions during the early tuber-bulking or root-development period
• Neutral to alkaline soil pH, which favours the pathogenic organism
• A field history of susceptible crops or high organic matter where scab-causing strains are present
• Irrigation gaps at the critical early infection window

Because infection is concentrated in a narrow early window and is strongly influenced by soil moisture and pH, prevention focuses on managing conditions during that period rather than treating the disease after lesions form.

• Maintain consistent soil moisture, particularly during early tuber or root set
• Avoid raising soil pH above the level needed for the crop being grown
• Rotate away from susceptible hosts where scab has been a recurring problem
• Choose less-susceptible varieties where available