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Potato Scab -
Streptomyces species
Helen Atthowe - Missoula County Extension
 HOSTS: Potato and sometimes red beets.
- DESCRIPTION: Tuber surfaces have areas that are brown, roughened, raised or pitted, and warty-looking.
LIFE CYCLE: Potato scab bacteria survives in the soil in the absence of host plants; it can attack the roots of weeds and other root crops. The potato scab bacteria is inhibited at soil pH higher than 7.4 and lower than 6.0. Optimum soil pH for scab is 7.0. The bacteria invades through lenticels when potato tubers are developing during the first 5 weeks after planting. If potato tubers dry out during this period, they are much more susceptible to scab.
CONTROLS:
CULTURAL: Be careful not to let potato soil dry out during early tuber development. Good moisture from one week before first shoots emerge until eight weeks after emergence can greatly reduce scab severity. Research has shown that the microorganisms surrounding potato tuber lenticels are antagonistic to the scab bacterium under high but NOT under low soil moisture conditions. Mulching with straw (as long as soil has good drainage) may help to maintain higher moisture levels and discourage scab. Resistant cultivars include: 'Superior' (susceptible to verticillium wilt), 'Russet Burbank', 'Pungo', 'Rhinered', 'Onoway', 'Russian Banana', 'Beltville', and 'Norland'.
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