HPIPM:Potato Common Scab

Taxonomy

Domain	Bacteria
Phylum	Actinomycetota
Subclass	Acidimicrobiidae
Order	Acidimicrobiales
Family	Streptomycetaceae
Genus	Streptomyces

Scientific Name

Streptomyces scabiei

Scientific Name Synonyms

Actinomyces scabies

Oospora scabies

Common Name

common scab of potato

Author: Howard F. Schwartz and David H. Gent

Identification and Life Cycle

Common scab is caused by at least three species of filamentous bacteria in the genus Streptomyces, and occurs in most potato production areas of the world. The pathogens resemble fungi in culture, but unlike most bacteria, produce spores. S. scabies is probably the most important species causing common scab in the High Plains region. Disease is initiated when soilborne or seedborne bacteria infect tubers through lenticels and produce toxins that cause excessive cell growth and death. Disease is most severe in warm, dry soils. The common scab pathogens can infect many diverse seedlings, but the role of this infection is unclear in the epidemiology of the organism. The pathogens survive between potato crops in seed tubers, soil, and perhaps pathogenically on other plants.

Plant Response and Damage

Common scab symptoms occur almost exclusively on tubers, but Streptomyces spp. reportedly infect stolons as well. Early disease symptoms on tubers are browning and excessive cell growth, but mature lesions are 0.2 to 0.4 inches and circular to irregular in shape. Lesions often grow together with time. At harvest, lesions may be superficial (russet scab), slighty raised (erumpent scab), or sunken (pitted scab). The types of lesions that develop are probably related to the strain of Streptomyces, environmental conditions, and timing of infection. Common scab does not reduce yield, but reduces tuber quality and grade.

Biological Control

No biological control practices have been developed for common scab.

Cultural Control

Plant high quality seed free from common scab. A three to four year rotation to other crops provides some disease suppression, but does not eliminate the pathogens from soil. Varieties vary widely in their disease reaction, and resistant or less susceptible varieties should be planted if available. Avoid high pH soils and amendments that increase soil pH. Maintaining high soil moisture (near field capacity) for four to six weeks beginning at tuber initiation will reduce disease incidence and severity.

Chemical Control

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.