<i>Cryphonectria parasitica</i> is the introduced fungus causing chestnut blight on American chestnut (<i>Castanea dentata</i>). The blight epidemic has decimated chestnuts throughout its native range. This necrotrophic fungus enters the host through wounds in the outer bark and rapidly kills host cells. Once infected, the cambium and inner bark become necrotic resulting in a canker that can expand and girdle a stem. However, we have observed secondary saprotrophic fungi that colonize the center of older blight cankers. These fungi were collected from natural cankers in chestnut stands in Michigan and Wisconsin and identified as <i>Trichoderma</i> spp. and <i>Penicillium</i> spp., which are noted in the literature to be competitive soil saprotrophs. To begin evaluating the potential of these secondary fungi as biological control agents, a dual-culture plating experiment was initiated to compare <i>in vitro </i>growth responses of two different strains of <i>Cr. parasitica</i> separately against nine isolates of secondary fungi. When plated against each of three strains of <i>Trichoderma</i> spp., the two strains of <i>Cr. parasitica</i> used in this study (EP 155 and LE 221) grew significantly less compared to the no competitor control. <i>Penicillium</i> spp. did not significantly change the growth of either strain of <i>Cr. parasitica</i> nor did the other four taxa of secondary fungi. Future research will investigate the ability of <i>Trichoderma</i> spp. to control canker expansion on excised and living chestnut tissue.
