Economical Biological Control of Sclerotinia Lettuce Drop bySporidesmium sclerotivorum

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Abstract
In a field trial, lettuce plants infected with Sclerotinia minor were treated with a preparation of Sporidesmium sclerotivorum at rates of 0, 0.2, 2, or 20 kg/ha of Sporidesmium product in May 1987. From the fall of 1987 to the fall of 1989, five successive lettuce crops were grown in this field with no additional application of the biocontrol agent. Disease incidence was significantly lower than the nontreated plots at the highest, two highest, and all three rates in the first, second, and third crop, respectively. In the third crop, 53, 68, and 72% disease control was obtained at the 0.2, 2, and 20 kg/ha rates, respectively. There were no differences in disease incidence among treatments in the last two crops due to an increase in indigenous populations of Sporidesmium in the nontreated plots. In October 1987, population densities of S. minor were significantly lower in plots treated with 2 or 20 kg/ha than in nontreated plots or plots treated with 0.2 kg/ha. By 1989, populations of S. minor in all treatments were low due to activity of the biocontrol agent. Estimated cost of the three rates of application is $2, 20, and 200/ha, respectively.