Common Scab

Scabby knees and elbows may be a normal part of childhood, but it’s not what you want to see on your potatoes or other root vegetables.

Common scab of potato (Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org) CC BY 3.0

Unlike apple scab, which is a fungal disease of fruits, common scab is a bacterial disease that prefers life underground. The actinobacteria responsible for common scab, Streptomyces, are found everywhere. Most commonly occurring in potatoes, beets, carrots, parsnips, radishes, rutabagas, and turnips may also become infected with common scab.


Common scab symptoms

Common scab looks exactly how it sounds. Surface russeting is the first thing you notice about plants with common scab. If you look deeper, you will also see deep pits in your tubers and root vegetables. Luckily, infected plants are safe to eat. Simply cut away the bad bits and toss them into the compost pile.


Common scab lifecycle

Common scab bacteria overwinter in infected roots and tubers left in the soil. Bacteria can also be spread via wind and rain splashing. Bacteria enter roots and tubers through natural openings, such as stoma, and wounds from insect feeding and shovels. The infection starts on the surface and works its way inward. These bacteria feed on the roots and tubers and will continue to reproduce for as long as temperatures are warm enough.


Common scab management

Common scab occurs most often in dry soils. This means that regular irrigation goes a long way toward preventing common scab in root vegetables. Common scab is more likely in soils with a pH greater than 5.2, so acidifying alkaline soils may also help prevent scabbing. Finally, rotate your potatoes and other root crops with non-tubers and watch for resistant cultivars when shopping for seeds and seedlings.