The Relative Importance of Weather, Soil‐ and Seed‐borne Inoculum in determining the Incidence of Common Scab ( Streptomyces scabies ) in Potato Crops

SUMMARY Potato seed tubers, cv. Majestic, without or variously affected by common scab, were planted between 1964 and 1967, in two fields at Rothamsted, one known to produce only slightly scabbed and the other severely scabbed potato crops. The amount of scab at lifting depended most on whether June or early July was wet or dry. If wet, there was little infection on progeny tubers irrespective of the amount of inoculum in soil or on seed tubers. When dry weather allowed infection, inoculum in soil had more effect than that on seed.