Potential for Biocontrol of Sclerotinia sclerotiorum Through Colonization of Sclerotia by Trichoderma harzianum. G. R. Knudsen, Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow 83843. D. J. Eschen, L. M. Dandurand, and L. Bin. Department of Plant, Soil and Entomological Sciences, Department of Bacteriology and Biochemistry, and Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow 83843. Plant Dis. 75:466-470. Accepted for publication 20 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0466.

In the laboratory, Trichoderma harzianum strain ThzID1, formulated as mycelial fragments in alginate pellets with or without wheat bran incorporated, colonized sclerotia of Sclerotinia sclerotiorum in raw or steamed soil. Incidence of colonization was higher in steamed soil than in raw soil, higher at 25 C than at 15 C, and higher at –500 kPa than at –50 kPa but was not affected by bran in pellets. Some sclerotia were colonized by indigenous Trichoderma spp. Pellets containing T. harzianum were added to soil in a pea (Pisum sativum) field or field microplots at densities of 4 × 10²–2 × 10⁴ pellets per square meter, along with sclerotia of S. sclerotiorum. Recovery of Trichoderma spp. from soil samples was not significantly increased by adding pellets. Addition of T. harzianum at high density (1 × 10⁴ or 2 × 10⁴ pellets per square meter) significantly increased the proportion of sclerotia colonized in microplots.