Biological Control of Sclerotinia Lettuce Drop in the Field bySporidesmium sclerotivorum

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Abstract
S. sclerotivorum, a mycoparasite of Sclerotinia spp., was evaluated under field conditions as a biological control agent for lettuce drop caused by Sclerotinia minor. The mycoparasite was applied to the field plots in May 1978 at 0, 1, 10, 100 and 1000 conidia/g (c/g) of soil. During the summer of 1978, S. sclerotivorum caused a 75-95% reduction in the numbers of sclerotia of S. minor in plots that had received 100 and 1000 c/g of soil, respectively, compared to only 25% in the control. Disease control in these plots for 4 consecutive lettuce crops during the spring and fall of 1979 and 1980 varied from 40 to 83% compared with the disease incidence in the untreated plots. The mycoparasite became established in the field plots and caused infection and subsequent destruction of sclerotia produced on the diseased lettuce. S. sclerotivorum has the potential to be a useful biological control agent for lettuce drop.