Potato scab is a serious disease affecting cultivated potato. Combinations of an inoculant application (Streptomyces sp. strain WoRs-501) and other control methods were tested for their ability to suppress potato common scab. The use of a moderately resistant variety of potato in combination with the soil application of WoRs-501 decreased an inoculant population of this strain required for suppressing scab disease as compared to a susceptible variety. When a susceptible variety of potato grown in paper pots was planted in a scab-infested field, the application of a small volume of WoRs-501 inoculum to soil in paper pots tended to increase the scab control effect. The incorporation of lopsided oat seedlings derived from seeds coated with a mycelial suspension of WoRs-501 into scab-infested soil as green manure prior to planting a susceptible variety of potato in pots tended to increase the disease-suppressive effect of lopsided oat, and would be a practical method of providing a significant disease-suppressive effect. Furthermore, when tubers of a susceptible potato variety coated with WoRs-501 suspension in 0.1% sodium carboxy methyl cellulose (CMC) were planted in pots, the disease incidence score was significantly reduced to almost the same level as that of NEBIJIN powder. The treatment of CMC alone at a concentration of 0.1% also tended to decrease the disease incidence score, suggesting that it could be a new candidate agent for practical disease control.