Contributions of stomatal infiltration and cuticular penetration to enhancements of foliar uptake by surfactants

Radiolabelled deoxyglucose (DOG) and glyphosate were used to investigate the effects of certain non-ionic surfactants on the kinetics of foliar uptake in three species. 'Silwet L-77' (5 g litre-1, an organosilicone surfactant, enabled spray solutions to infiltrate stomata, providing uptake of DOG into Vicia bean (50%), oat (35%) and wheat (20%) within 10 min of applicatiion. 'Silwet Y-12301', another organosilicone, also induced stomatal infiltration but to a lesser extent: unlike L-77, this attenuate by partial stomatal closure. A third organosilicone, 'Silwet L-7607', and two conventional surfactant, 'Triton X-45' (OP5) and 'Agral 90' (NP9), did not induce stomatal infiltration. The effective minimum concentration of L-77 required to enable infiltration of stomata was 2 g litre-1. The uptake of glyphosate into bean did not differ that of DOG but the 'Roundup' formulation of glyphosate partially antagonised the infiltration provided by L-77. Addition of surfactants did not increase the rate of cuticular penetration of DOG into bean but total uptake was increased, except by NP9, either via infiltration (L-77 and Y-12301) or by extending the period during which penetration occurred (L-7607 and OP5). The surfactants had a variable effect on rates of penetration of DOG into wheat and oat. In general, foliar uptake followed an exponential timecourse which was largely complete within 6 h and only rarely approached 100% of the applied chemical. The stomatal infiltration provided by L-77 caused an increase in translocation of DOG in bean.