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(P372) Assessing the risk to non-target plants from a corn herbicide .
Dobbs, Michael*,1, Ramanarayanan, Tharacad1, Warren-Hicks, William2, Qian, Song2, Giddings, Jeffery3, Kelly, Iain1, Allen, Richard1, Fischer, Reinhard1, 1 Bayer CropScience, RTP, NC, USA2 The Cadmus Group, Durham, NC, USA3 The Cadmus Group, Marion, MA, USA
ABSTRACT- There is limited regulatory guidance on how to perform higher tier non-target plants risk assessments for herbicide use, although general ecological risk assessment techniques are applicable. Methods to perform probabilistic risk assessments for non-target plants have been explored for the corn herbicide BALANCE, which contains isoxaflutole and is applied pre-emergence to control a broad spectrum of weeds. Because of the potentially close relationship between the target species, and species to be protected, definition of the protection goals for the risk assessment is critical. Protection goals must consider ecological, societal, and economic values, along with practical considerations, and should be designed to protect valued resources. In the case of isoxaflutole, the risk that its labeled use on corn poses to non-target plants was investigated based on two potential routes of exposure: spray drift and runoff. A Bayesian hierarchical modeling framework was used to evaluate the laboratory toxicity data and generate species sensitive distributions. This approach allowed incorporation of data from multiple studies and includes variability from all sources in the analysis. The field data and commercial use experience provided important checks on the laboratory estimates. It was found that BALANCE was unlikely to permanently affect emerging plants outside of the field margins. Established vegetation closest to the field margins may experience transient effects due to exposure from spray drift or runoff, but long-term effects on crop yield, community productivity, or community structure are unlikely. Field data and commercial use experience confirm no long-term impacts on non-target plants from BALANCE use on corn.
Key words: Isoxaflutole, Non-Target Plants, Probabilistic Risk Assessment, Herbicide
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