Estimating input data for computations on the volatilisation of pesticides from plant canopies and competing processes

Volatilisation of pesticides from the crop can be an important emission pathway to the environment. A computation module was developed for making estimates on this emission. However, various input data for this module are not measured directly in registration procedures, so they have to be estimated from theory or from a diversity of experimental data. Vapour pressure is the most important property in volatilisation, which needs a critical evaluation in case of conflicting data. Diffusion coefficients for transport in a laminar boundary layer are estimated from theory. Penetration of pesticides into the leaves is highly affected by substances in the formulation and by environmental conditions. Pesticide deposit is often vulnerable to washoff by rainfall. Often, no directly measured rates are available for photochemical transformation on plant surfaces, so these have to be estimated from a variety of experimental results. In critical cases, comprehensive experiments with micro-agro-ecosystems and/or in the field are needed.