Evaluation of Single Annual Applications of Sterol-Inhibiting Fungicides for Control of Pine Twisting Rust. Marie-Laure Desprez- Loustau, Institut National de la Recherche Agronomique, Station de Pathologie Végétale, BP 81, 33883 Villenave d’Ornon Cedex, France. Fabrice Dupuis, and Anne Viguié. Institut National de la Recherche Agronomique, Station de Pathologie Végétale, BP 81, 33883 Villenave d’Ornon Cedex, France. Plant Dis. 76:376-382. Accepted for publication 25 June 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0376.

Six sterol biosynthesis inhibiting (SBI) fungicides—cyproconazole, flusilazole, flutriafol, tebuconazole, triadimefon, and triadimenol—were tested against Melampsora pinitorqua, the causal agent of pine twisting rust. Triadimefon and cyproconazole provided the highest level of control in seedling and cut-shoot bioassays. At 500 mg a.i./L, 2–4 wk of protective activity and at least 5 days of curative activity were observed. Cyproconazole appeared much more fungitoxic than triadimefon toward seven ectomycorrhizal fungi. The efficacy of a single application of triadimefon was tested under field conditions. Results demonstrate that triadimefon has a good potential for practical control of pine twisting rust. The cut-shoot technique appears to be a valuable tool for screening fungicides. In contrast, basidiospore germination appears to be an unsuitable criterion for assessing SBI efficacy.