Chronic effects of strobilurin fungicides on development, growth, and mortality of larval Great Plains toads (Bufo cognatus).

Agricultural fungicide application has increased tenfold since 2005 in the United States. Active ingredients and formulations of strobilurin fungicides at environmentally relevant concentrations cause mortality to larval and metamorph amphibians; however, little is known about chronic exposure effects in amphibians. We exposed larval amphibians (Bufo cognatus) throughout metamorphosis to the common fungicide formulations Headline(®), Stratego(®), Quilt(®), and a control to determine effects on development and growth. Formulations were tested at 1.7, 50, and 400 μg/L of the active strobilurin ingredient for Headline(®), Stratego(®), and Quilt(®), respectively. Fungicide exposure did not affect body mass or snout-vent length at metamorphosis. However, exposure to Headline(®) at 1.7 μg/L increased the development rate of tadpoles by approximately 5 days compared to the control, an effect not observed for Stratego(®) and Quilt(®). Stratego(®) also caused approximately 35 % cumulative mortality. Results from the experiment suggest that chronic effects of strobilurin fungicides on development, growth, and mortality to B. cognatus are apparent at environmentally relevant concentrations.