Pacific Pests, Pathogens, Weeds & Pesticides - Online edition

Pacific Pests, Pathogens, Weeds & Pesticides

Potato black scurf (295)

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Photo 1. Underground stem of potato with cankers caused by black scurf, Rhizoctonia solani.

Photo 2. Close-up of underground stem of potato showing cankers caused by black scurf, Rhizoctonia solani.

Photo 3. Black scurf, the name given to the appearance of potato tubers when sclerotia of Rhizoctonia solani form on the surface.

Summary

  • Worldwide distribution. On potato, rice, and more. Many strains. An important disease.
  • Brown sunken cankers on stems and stolons, limiting tuber growth and causing wilts, stunting and death. Balls of fungus in black rinds ('sclerotia') on tubers. It also causes seedling damping-off.
  • Spread in movement of soil and seed.
  • Cultural control: certified seed; best to sprout seed, inspect, then plant; remove volunteers; avoid, cold wet soils and plant only 5 cm deep so that the warm soil encourages rapid shoot growth; improve field drainage; manure; 3-year rotation; harvest as soon as tops removed; collect and burn trash after harvest.
  • Chemical control: seed - treat with pencycuron or mancozeb.

Common Name

Black scurf, rhizoctonia canker

Scientific Name

Rhizoctonia solani. It is also called Thanatephorus cucumeris, which is the sexual state; it may occur on the lower stems of potato. There are a number of strains, and the common one on potato is referred to as AG3.

Photo 4. The cottony growth (mycelium) of black scurf, Rhizoctonia solani.

AUTHOR Grahame Jackson 
Information from Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, et al. CSIRO Publishing; and from Wharton P, Wood E (undated) Rhizoctonia stem canker and black scurf of potato. University of Idaho Extension. (https://www.cals.uidaho.edu/edcomm/pdf/CIS/CIS1198.pdf). Photos 1-3 Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org. Photo 4 Bouchek-Mechiche K (2016) Black scurf. GNIS/INRA. (https://www.potato-tuber-blemishes.com/Symptoms/Pitted-or-raised-symptoms/Black-scurf).

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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