One of the most important ways to improve the efficacy of pesticides and minimize their impact on off-target organisms is through increasing the penetration of active ingredients into plant foliage. Foliar uptake of pesticides is a complex process, depending on leaf surface characters of plants, physicochemical properties of the chemicals, types and concentration of the additives, and environmental conditions.
The fundamental mechanism of uptake has been considered, with most attention given to the epicuticular lipids and their role in modifying active ingredient diffusion through cuticles (Kirkwood 1999; Riederer and Marksta¨dter 1996; Scho¨nherr et al. 1999). However, there is a much simpler effect on the leaf surface that needs to be considered first. If a spray formulation contains adjuvants that cause droplet spread on a leaf surface, this will in effect lower the mass of active per unit area without any change in concentration until the spray solution begins to evaporate. In any case, there will be a ‘‘solution residue’’ where the concentration of the active is many times more than in the starting spray solution (Zabkiewicz 2003).
Adjuvants are known to facilitate cuticular ‘‘transport’’ (foliar uptake) but are not thought to play any significant part in further short- or long-distance translocation processes. However, in theory, if adjuvants could reach the cellular plasmalemma, then they could affect the initial stage of the sub-cuticular transport process. The recent use of mass or molar relationships, instead of percentages, for xenobiotic uptake into plants from differing formulations, may be a means of elucidating some of the interactions among actives, adjuvants and plants (Forster et al. 2004).