International Fungicide Efficacy Trials for the Management of Soybean Rust.

The efficacy of fungicides in managing soybean rust was evaluated in 12 environments in South America and southern Africa over three growing seasons from 2002 to 2005. There were differences in final soybean rust severity, defoliation, and yield among the treatments at most locations. In locations where soybean rust was not severe, all the fungicides evaluated reduced severity. In locations where soybean rust was severe, applications of triazole and triazole + strobilurin fungicides resulted in lower severity and higher yields compared with other fungicides. The strobilurin fungicides provided the highest yields in many locations; however, severity tended to be higher than that of the triazole fungicides. There also were differences in yield and severity between the trials with two and three applications of several fungicides, with three applications resulting in less severe soybean rust and higher yields. However, the third application of tebuconazole, tetraconazole, and the mixtures containing azoxystrobin and pyraclostrobin was not needed to maintain yield. These fungicides were among the most effective for managing soybean rust and maintaining yield over most locations.