Control of tuber-borne black scurf [Rhizoctonia solani] and common scab [Streptomyces scabies] of potatoes with a combination of sodium hypochlorite and thiophanate-methyl preplanting seed tuber treatment

In a 2-year field experiment, preplanting seed tuber treatments with sodium hypochlorite solution (as NaOCl 500 ppm for 8 min). thiophanate-methyl (TP M; as Easout (TM), 50 g active ingredients/100 kg seed tubers), or a combin ation treatment with NaOCl followed by TPM were evaluated for control of bl ack scurf, caused by Rhizoctonia solani Kuhn, and common scab, caused by St reptomyces scabies (Thaxter) Lambert & Loria, on potato, Solanum tuberosum L., cv. Russet Burbank. The combination treatment with NaOCl and TPM reduce d Rhizoctonia on progeny tubers at harvest and after storage. The low incid ence of scab on progeny tubers, in untreated checks, hindered the evaluatio n of the efficacy of the combination treatment and also showed that conditi ons were not Favourable for scab development during this period and at this location. A comparison between NaOCl and the combination treatment indicat es that preplanting NaOCl treatment may have killed the majority of the bla ck scurf sclerotia on the tuber surface and that the combination TPM fungic ide treatment following NaOCl disinfection suppressed the growth of the R. solani. A higher (1995) or similar (1996) marketable yield in the combinati on treatment compared to that in the untreated check showed that there was no phytotoxicity in the treated tubers. Disease incidence of black scurf an d common scab varied from year to year. The results confirm that tuber-born e inoculum of R. solani reduces progeny tuber quality and marketable yields .