Control of skin spot and silver scurf on stored cv. King Edward potatoes by chemical and non-chemical methods

In 3 years, seed tubers of cv. King Edward were planted in field experiments and diseases assessed on the daughter tubers after storage for 24-26 wk. In 1991 and 1992, the seed tubers were treated with a mixture of thiabendazole and imazalil at two rates. Tubers were harvested on several dates from late August to early October and dried under different conditions before storage. In 1990, silver scurf after storage was decreased equally by dry curing for 2 wk and windrowing for 2 h whereas skin spot was decreased most by dry curing, and these effects were greater the earlier tubers were harvested. In 1991, dry curing for 2 wk decreased skin spot and silver scurf more than dry curing for 1 wk, and skin spot was slightly decreased by windrowing for 2 h; windrowing improved the control of both diseases when tubers were subsequently dry cured. In 1991 and 1992 fungicide treatment of seed tubers greatly decreased skin spot after storage and was also effective against silver scurf, but increased black dot when tubers were harvested in September or October. Skin spot was controlled equally well by the two rates of fungicide but silver scurf was less well controlled when the dose was decreased by 75 %. It is suggested that amounts of fungicide applied to seed tubers could be decreased provided that the efficiency of application is improved and that crops are harvested early and dried before storage.