Pacific Pests, Pathogens and Weeds - Online edition

Pacific Pests, Pathogens, Weeds & Pesticides

Potato powdery scab (294)

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  • Worldwide distribution. On potato, but also tomato, capsicum, and weeds in the potato family. It is related to the club root of brassicas (see Fact Sheet no. 283). An important disease.
  • Resting spores in the soil produce swimming spores which infect all underground parts. On tubers, wart-like, powdery, roughly circular 'scabs' 10 mm diam. on the surface, merging and containing resting spores. Dark galls 1-10 mm diam. on roots.
  • Disease reduces quality (and price), affects processing, and transfer a serious virus.
  • Spread occurs in soil on machinery, shoes, and via manure if cattle fed diseased tubers. Long distance spread on tubers for seed and trade.
  • Cultural control: disease free (certified) tubers; improve drainage; avoid fields where disease known to occur (spores last up to 10 years); do not use manure from animals fed diseased tubers; avoid excessive amounts of N; crop rotation for >3 years.
  • Chemical control: treat tubers with mancozeb..
Common Name

Powdery scab

Scientific Name

Spongospora subterranea f.sp. subterranea. It is a member of the family Plasmodiophoraceae, the same family as that of Plasmodiophora brassicae, the cause of club root of brassicas (see Fact Sheet no. 283). Like Plasmodiophora brassicae, powdery scab belongs to a group called rhizaria in the Kingdom Protista; they are related to slime moulds.

AUTHOR Grahame Jackson 
Information from Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, et al. CSIRO Publishing; and from Powdery scab (2016) Wikipedia. ( Photos 1-3 Sandra Jensen, Cornell University, Diagram Steven B Johnson (2002) Bulletin No. 2436, Powdery Scab of Potatoes. The University of Maine. (

Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community. 

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