A compartmental computer model of foliar uptake of pesticides

The uptake and movement of a chemical into a wheat leaf has been simulated in a 5‐compartment model. The compound is considered to be applied to the leaf as discrete droplets of solution, from which water evaporates at a uniform rate. Solute diffuses from the droplets through the plant cuticle into the epidermal cell wall, and from there either into and out of the cytoplasm and vacuole of the mesophyll cells or along cell walls to the xylem. Once in the xylem it is carried in the transpiration stream towards the tip of the leaf. Accurate values for the parameters required by the model have not yet been measured, but the model simulates in a qualitative manner the movement pattern observed for 1‐methyl‐2‐pyridone. The results presented focus attention on the possible importance of membrane permeability in determining the phytotoxicity of xylem mobile pesticides.