Effects of physical properties on the translaminar activity of fungicides.

Translaminar redistribution is a key component of activity for many fungicides. The influence of physical properties (including water solubility, lipophilicity, melting point, and molar volume) on translaminar activity, however, is not well understood. Cucumber powdery mildew was used as a biological indicator to examine the influence of physical properties on translaminar activity of 61 fungicides in simple, uniform formulations, including three modes-of-action and a range of physical properties. Results were modeled using multiple regression and ordinal logistic fit. We confirmed that translaminar activity is a frequent attribute of fungicides and that lipophilicity and water solubility are important predictors of translaminar activity. The hypothesis that melting point drives translaminar movement and translaminar activity was not supported. Translaminar movement (driven only by physical properties) could be differentiated with the models from fungitoxicity-influenced translaminar control. Translaminar activity is a complex attribute and differences in inherent activity as well as physical properties and formulations must be considered when comparing compounds for relative translaminar activity.

AgDRIFT: a model for estimating near-field spray drift from aerial applications.

The aerial spray prediction model AgDRIFT embodies the computational engine found in the near-wake Lagrangian model AGricultural DISPersal (AGDISP) but with several important features added that improve the speed and accuracy of its predictions. This article summarizes those changes, describes the overall analytical approach to the model, and details model implementation, application, limits, and computational utilities.

Evaluation of the AgDISP aerial spray algorithms in the AgDRIFT model.

A systematic evaluation of the AgDISP algorithms, which simulate off-site drift and deposition of aerially applied pesticides, contained in the AgDRIFT model was performed by comparing model simulations to field-trial data collected by the Spray Drift Task Force. Field-trial data used for model evaluation included 161 separate trials of typical agriculture aerial applications under a wide range of application and meteorological conditions. Input for model simulations included information on the aircraft and spray equipment, spray material, meteorology, and site geometry. The model input datasets were generated independently of the field deposition results, i.e., model inputs were in no way altered or selected to improve the fit of model output to field results. AgDRIFT shows a response similar to that of the field observations for many application variables (e.g., droplet size, application height, wind speed). However, AgDRIFT is sensitive to evaporative effects, and modeled deposition in the far-field responds to wet bulb depression whereas the field observations did not. The model tended to overpredict deposition rates relative to the field data for far-field distances, particularly under evaporative conditions. AgDRIFT was in good agreement with field results for estimating near-field buffer zones needed to manage human, crop, livestock, and ecological exposure.