Biomass Reducing Potential and Prospective Fungicide Control of a New Leaf Blight of Miscanthus × giganteus Caused by Leptosphaerulina chartarum

During a multistate survey (2009) of diseases of perennial grasses under consideration as biofuel feedstocks, a new leaf blight of Miscanthus × giganteus caused by Leptosphaerulina chartarum was observed on 100 % of the plants evaluated in research plots near Lexington, Kentucky. A greenhouse study was conducted to evaluate the effect of L. chartarum on M. × giganteus biomass and to identify effective foliar fungicides against the disease. Eleven broad-spectrum fungicides were tested with rates typically used in agronomic crops. Fungicides tested included active ingredients from five different chemical groups, demethylation inhibitors (prothioconazole, tebuconazole, cyproconazole, propiconazole, tetraconazole, flutriafol, and metconazole), quinone outside inhibitors (pyraclostrobin), succinate dehydrogenase inhibitors (boscalid), methyl benzimidazole carbamates (thiophanate-methyl), and chloronitriles (chlorothalonil). Infection by L. chartarum significantly lowered aboveground biomass by an average of 33 %. Application of cyproconazole, flutriafol, tebuconazole, or prothioconazole significantly reduced disease severity, with cyproconazole and flutriafol ranking best at an average of 29 % disease control. However, no fungicide treatment resulted in biomass loss abatement. Greater rates or a combination of fungicides might be needed to achieve adequate control.