Introduction
White mold, caused by Sclerotinia sclerotiorum (Lib.)
de Bary, is a serious problem in a large number of
sprinkler-irrigated potato (Solanum tuberosum L.)
fields in Hamadan, Iran (Ojaghian 2009). Although there are few reports of severe damage of this fungus on potato (Partyka and Mai 1961), this disease usually causes considerable yield loss in Hamadan. A number of control measures have been suggested to manage sclerotinia diseases but because of the wide host range of this pathogen, longevity of sclerotia (Gerlagh et al. 1999), possible infection byascospores from neighboring fields, the lack of resistant potato cultivars (Atallah and Johnson 2004) and economic or environmental concerns,there is no simple and effective control procedure to manage sclerotinia diseases economically and