Terrestrial exposure and effects of Headline AMP® Fungicide on amphibians

Recent studies have demonstrated that a pyraclostrobin-containing fungicide (Headline® Fungicide—Headline® Fungicide and Headline AMP® Fungicide are registered trademarks of BASF) is toxic to amphibians at environmentally relevant concentrations. However, these studies were performed in a laboratory setting of a worst-case direct exposure in clean media. Interception of spray by the crop canopy and ground cover used by animals for security cover will influence exposure. Thus, risk to amphibians is unclear in an environmentally realistic field environment. We tested exposure and toxicity of Headline AMP® Fungicide to amphibians in multiple agricultural habitat scenarios (e.g., within treated crop vs. grassy areas adjacent to crop) and at two rates during routine aerial application. Specifically, we placed Woodhouse’s toads (Bufo woodhousii) and Blanchard’s cricket frogs (Acris blanchardi) in enclosures located within treated and untreated corn (VT stage, approximate height = 3 m), and in the potential drift area (adjacent to treated corn) during aerial application of Headline AMP Fungicide at either 731 or 1052 ml/ha (70 and 100 % the maximum application rate in corn, respectively). Mean concentrations of pyraclostrobin measured at ground level were ≤19 % of nominal application rate in all areas. Overall, mean mortality of recovered individuals of both species was ≤15 %, and mortality within Headline AMP Fungicide-treated corn (where risk was anticipated to be highest) was <10 %. It is important to understand that application timing, interception by the crop canopy (which varies both within and between crop systems), and timing of amphibian presence in the crop field influences risk of exposure and effects; however, our results demonstrate that amphibians inhabiting VT stage corn during routine aerial application of Headline AMP Fungicide are at low risk for acute mortality, matching existing laboratory results from acute toxicity studies of Headline Fungicide.