FUNGICIDE TREATMENT OF SEED TUBERS INFECTED WITH THIABENDAZOLE-RESISTANT HELMINTHOSPORIUM-SOLANI AND POLYSCYTALUM-PUSTULANS FOR CONTROLLING SILVER SCURF AND SKIN SPOT ON STORED PROGENY TUBERS

Seed tubers, cv. Desiree, derived from stocks treated annually with thiabendazole were infected with thiabendazole-resistant strains of Helminthosporium solani and Polyscytalum pustulans. Samples of seed tubers were either untreated or immersed for 5 min in fungicide suspensions of thiabendazole, imazalil or thiabendazole plus imazalil and planted on four farms in 1988 and 1989. After harvest, tuber samples from each treatment were treated with thiabendazole and stored for 6 months. Applying imazalil or thiabendazole plus imazalil to seed tubers decreased the severity of silver scurf and skin spot on stored progeny tubers. Thiabendazole applied to seed tubers or to progeny tubers after harvest did not affect the severity of either disease, but post-harvest treatment decreased the incidence of black scurf after storage.