Biological Control of Septoria Leaf Spot of Poplar by Phaeotheca dimorphospora . D. YANG, Postdoctoral Researcher, Centre de Recherche en Biologie Forestiere, Faculte de Foresterie et de Geomatique, Universite Laval, Sainte-Foy, Quebec, Canada G1K7P4. L. BERNIER, Assistant Professor, and M. DESSUREAULT, Professor, Centre de Recherche en Biologie Forestiere, Faculte de Foresterie et de Geomatique, Universite Laval, Sainte-Foy, Quebec, Canada G1K7P4. Plant Dis. 78:821-825. Accepted for publication 10 May 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0821.

Phaeolheca dimorphospora, a Deuteromycotina fungus found to be antagonistic in vitro against Septoria musiva and other tree pathogens, was tested for its ability to suppress Septoria leaf spot on poplar. In an in vitro leaf disk assay, P. dimorphospora significantly reduced the size of the necrotic area caused by S. musiva on Populus tremuloides, P. grandidenlala, and P. ? berolinensis. In the greenhouse, both pre- and posttreatment of cuttings of P. ? berolinensis with P. dimorphospora resulted in a significant reduction in the severity and in the rate of development of Septoria leaf spot. P. dimorphospora was reisolated from poplar leaves I mo after inoculation. Application of P. dimorphospora culture filtrate and its medium extract on the foliage of poplar also reduced disease severity.