Common scab

Streptomyces scabies

Symptoms

• Symptoms vary from superficial to deep (star/crater shapes up to 1.5 cm)
• Starts as infection on the lenticels
• The surrounding cell layers become corky and crack when the tuber grows
• This causes the typical star shape lesion and net pattern on the skin

Infection and spread

• Soil type, crop rotation and varietal sensitivity influence infection severity
• Key vulnerability during tuber formation
• High pH (6.5-8) and dry soil during tuber formation favour the infection
• Spread via seed tubers is negligible

Possible confusion with

• Powdery scab (Spongospora subterranea)
• Tobacco Necrosis Virus (TNV)