There are no above ground manifestations. Initial symptoms on potato tubers are small, purplish-brown pustules that increase slowly in size. They later burst, rupturing the skin of the potato tuber and liberating a dark brown powdery mass. Corky shallow notches known as scab appear. In high moisture soils, lesions expand inwards, forming deep pits and destroying internal tissues. Swellings and galls develop, and the deformed potatoes are not marketable. The anomalies may continue to grow during storage.
Powdery scab is caused by a soil borne pathogen that can survive up to 6 years in soils. The disease is common in cool temperatures (12 to 18°C) and heavy, acidic soils, that are prone to waterlogging. Alternating periods of wet and dry weather can also favor its development. Infected seed tubers, clothing, tools or manure can be carriers of the pathogen. The infection happens at tuber initiation through lenticels, eyes or wounds of the tubers. Russet potato varieties show fewer symptoms of damage. powdery scab can infect several members of the solanaceous family.
No alternative treatment against this pathogen is available
Always consider an integrated approach with preventive measures together with biological treatments if available. Pretreatments of soils with metam sodium or fluazinam work well in some cases, mostly depending of environmental conditions