Toxicity of soybean rust fungicides to freshwater algae and Daphnia magna

Soybeans are intensively grown over large swaths of land in the Midwestern US. Introduction of the pathogenic fungus responsible for Soybean Rust (Phakopsora pachyrhizi) will likely result in a significant increase in the environmental load of strobilurin and conazole fungicides. We determined the toxicity of six such fungicides to the unicellular algae Pseudokirchneriella subcapitata and the aquatic invertebrate, Daphnia magna. We found that levels of concern of some fungicides were lower than annual average runoff concentrations predicted for Indiana. Our results suggest that pyraclostrobin and propiconazole, and to a lesser extent tebuconazole, may cause impacts to algae and daphnids in areas where soybeans are intensively grown. More studies are needed to describe the ecological effects of sublethal exposures to these fungicides, as well as monitoring environmental concentrations in watersheds where these fungicides are applied to soybeans.