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Powdery Scab

Powdery Scab

Spongospora subterranea


In a Nutshell

    Pustules that contain dark spore material burst and produce corky notchesLesions expand inwards, forming deep pits and destroying internal tissuesOutgrowths slowly deform the potatoesAnomalies continue to grow during storage

Hosts: %1$s

· Potato


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.

Biological Control

No alternative treatment against this pathogen is available

Chemical Control

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

Preventive Measures

    Check with seed retailer on resilient varietiesUse healthy seeding materialImplement a well-coordinated crop rotationPlant in well-drained soils that are not susceptible to water-loggingCheck for alternative hosts of the solanaceous family in and around the field and eradicate themApply sulfur to your soils to control pHTake special care of the disinfection of your equipment, clothes and toolsDo not apply manure from animals that have been fed scabby potatoesDeep plow and soil solarization after harvest also help