Influence of Physicochemical Properties on Uptake and Loss of Pesticides and Adjuvants from the Leaf Surface

Adjuvants and glyphosate activity

“…This process can be subdivided into discrete stages involving the consecutive partitioning and diffusion of glyphosate through several barriers until it is finally loaded into the vascular tissues. The mechanisms which are thought to govern the transport of agrochemicals in plants have been reviewed in detail by Schönherr and Baur9 and Briggs and Bromilow 10. A summary for glyphosate is given in Fig 4; the movement of the herbicide through a barrier will be the summation of permeance (diffusion coefficient, path length and size selectivity of barrier) and the driving forces (partition coefficient, concentration and electrochemical gradient).…”

“…For glyphosate salts, the major factors limiting uptake are probably their partition and diffusion coefficients. For example, the octanol‐water partition coefficients are extremely low, 0.00001, with the corresponding epicuticular wax‐water values being even smaller 10. Nevertheless, investigations with the radiolabelled herbicide have shown that, if a high enough concentration of glyphosate is applied, then considerable amounts of the radiolabel are able to penetrate into leaves unaided 16, 30, 31.…”

Physicochemical property guidelines for modern agrochemicals

“…Briggs describes the role of melting point (mp) in the solubilization of a compound on the leaf surface. His very detailed analysis of the effects of mp versus log P on systemic behavior of agrochemicals showed that mp is a key property to consider.…”

Improving agrochemical performance: possible mechanisms for adjuvancy

“…Of greater importance is the interaction between the adjuvant and pesticide in the deposit, because for a pesticide to penetrate it must either be a liquid or in solution (Briggs and Bromilow, 1994). It is likely that some surfactants and oils act as solvents or solubilizing agents for pesticides, and this will have an important influence on the amount of pesticide available for uptake (Figure 8.16).…”

“…Adjuvants that are taken up by foliage will probably have additional sites of action and their possible effects on the penetration of pesticides can be considered in relation to the physico-chemical compartmentalized models proposed by Briggs and Bromilow (1994;Figures 8.17 and 8.18) and Schonherr and Baur (1994;Figure 8.19). These are concerned with rates of diffusion and the pivotal partition parameters logPa1k (alkane-water), providing an indication of the solubility of a pesticide in epicuticular wax,…”