Economic Importance

Yield losses due to Sclerotinia diseases in susceptible crops vary and may be as high as 100 per cent (Purdy, 1979). In vegetable and fruit crops, losses are due to the infected produce rotting in the field before harvest and also due to rotting during storage (Walker, 1969; Willetts and Wong, 1980). In seed crops, yields are reduced by both as reduction in seed size from the premature ripening of infected plants (Kruger, 1973, 1975b; Morrall et al., 1976) and by the loss of seed during harvesting. Seed loss is attributable to the replacement of seed by sclerotia in crops like sunflower and beans. The shattering of prematurely ripened seed pods before harvest and loss of quality in the form of smaller, shrunken and chaffy seed in crops like rapeseed and sunflower has been observed (Kruger, 1973, 1980; Morrall et al., 1976). The fungal sclerotia may be mixed with seeds of sunflower, rapeseed and beans (Hoes and Huang, 1976; Kruger et. al., 1981).

Losses of some crops from diseases caused by Sclerotinia sclerotiorum and other species of Sclerotinia are millions of dollars annually. The losses are directly from loss of yield and indirectly from lessened quality (loss in grade). There are no data to illustrate the loss of expenditures for attempts to control diseases caused by S. sclerotiorum, when attempts are either effective or non effective. There also is another form of loss caused by this pathogen, the production lost due to abandonment of fields for growing preferred crops for less lucrative ones, or to non crop plants, weeds or fallow (Purdy, 1979).