The off-target movement of herbicides may include volatility/air dispersion that leads to non-target organism vapor exposure. Pesticide flux loss and air dispersion modeling for soil fumigants are well established in the scientific literature. However, little historical work has been performed in developing or quantifying vapor phase dose-response (DR) curves for plants when contrasted against the plethora of DR observations based upon direct herbicide spray to plant foliage. A multi-compartment plant model is proposed to estimate pesticide vapor uptake by plants as well as translocation and bio-accumulation within plant compartments. This plant model was designed to account for topical exposure regimes (e.g., direct spray to foliage) and vapor phase (dry) deposition of an herbicide to leaf surfaces. Conventional DR observations are used with the plant model to estimate the internalized pesticide concentrations that lead to the observed phytotoxic response. This known/approximated internalized concentration DR can subsequently be used to explore potential responses when vapor exposure is the primary pathway, with vapor exposure quantified by conventional dry deposition mechanisms. Once a vapor phase DR function is known, the potential impact of vapor exposure to non-target plants can be quantified using conventional volatility and air dispersion modeling for herbicide exposure estimates. This work illustrates the two step process required if vapor phase DR functions are not known (but topical application DR functions are available). Model parameters for dicamba and triclopyr are obtained from independent literature data, volatility is approximated using the soil physics model proposed by Jury et al. 1983, and simulation results for plant injury from vapor exposure are presented and compared to literature values where correct order of magnitude predictions for sensitive crop injury are simulated.

Modeling of herbicide vapor phase uptake and injury to target plants

254th National Meeting (2017)

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