MANAGEMENT OF SILVER SCURF (HELMINTHOSPORIUM-SOLANI) WITH FUNGICIDE SEED TREATMENTS AND STORAGE PRACTICES

Thiabendazole insensitive strains of Helminthosporium solani, the caus al agent of silver scurf, make controlling the disease with seed treat ment difficult. Potato tuber seed treatments and environmental storage management practices were investigated as means to minimize silver sc urf. Fungicide seed treatments were evaluated for control of H. solani ; disease was evaluated during the growing season, at harvest, and aft er 5 months of storage. Silver scurf was observed on progeny tubers el even weeks after planting. Fungicides that reduced silver scurf incide nce and severity on the seed resulted in reduced incidence and severit y of the disease in the progeny tubers at harvest and significantly lo wer disease ratings after storage. Only small increases in disease inc idence (0-8%) were seen after storage, Thiophanate-methyl with mancoze b, Captan with mancozeb, and fludioxonil were among the most effective in reducing the incidence and severity of silver scurf on seed and in progeny tubers (Incidence on progeny tubers at harvest for these thre e treatments were 3%, 9%, and 8% respectively). Thiophanate-methyl alo ne was not effective for control of silver scurf (48% incidence compar ed to 43% incidence for the untreated control). Environmental conditio ns in storage affected disease development. Reduced humidity (85%) dur ing the curing period (0-3 weeks after harvest) significantly reduced (11%) the surface area of tubers infected with silver scurf. Free mois ture on the tuber surfaces during storage significantly increased (15% ) tuber surface area infection. H. solani was shown to survive in soil and on some potato storage building materials for up to 9 months. The silver scurf disease of potatoes can be suppressed using effective se ed treatment and storage management.