Worldwide distribution. On members of several plant families, potato, radish, parsnip; most important on potato. A cosmetic disease.
Appearance affects market quality, but not yield.
A soilborne bacterium causes corky pits, sometimes deep and joining together, up to 10 cm. Survives a long time in soil. Spread on tubers for planting.
Cultural control: healthy seed; avoid organic matter; remove volunteers; clean machinery, shoes, etc., to prevent spread to scab-free fields; 3-4-year crop rotation; collect and destroy infected tubers at harvest; avoid livestock going to fields after feeding on diseased tubers.
Chemical control: treat seed with captan or mancozeb