Reduced sclerotial soil-longevity by whole-crop amendment and plastic covering

The sclerotial survival of three plant pathogens (Sclerotinia sclerotiorum, Sclerotium cepivorum and Verticillium dahliae) was evaluated in field expe riments after amending soil with fresh whole crops of white mustard or oats , after covering the soil surface with opaque plastic sheers, or after comb inations of amendment and plastic covering. The whole crops were incorporat ed by rototilling; followed by burying, in the topsoil of each plot, labora tory-produced sclerotia within nylon- mesh bags. The experiments were then immediately irrigated before covering designated treatments with plastic. A fter 10 to 13 weeks, the buried sclerotia were retrieved, and sclerotial su rvival was assessed in the laboratory. Survival of S. sclerotiorum scleroti a was significantly affected by the treatment that combined plastic coverin g with soil amendment. Survival of V. dahlide sclerotia was affected by tha t same type of treatment, and, in addition, by plastic-covering alone, wher eas the survival of S. cepivorum sclerotia was unaffected regardless of tre atment. The sclerotia of S. sclerotiorum were inactivated heavily because t hey were attacked and colonized by fungi and bacteria; and in one of the fi eld experiments, the survival was strongly reduced for all treatments by th e mycoparasite Coniothyrium minitans. In contrast, no mycoparasites were ob served on retrieved sclerotia of S. cepivorum and V. dahliae.