EVALUATION OF SINGLE ANNUAL APPLICATIONS OF STEROL-INHIBITING FUNGICIDES FOR CONTROL OF PINE TWISTING RUST

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.