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 application. ‘Silwet Y‐12301’, another organosilicone, also induced stomatal infiltration but to a lesser extent; unlike L‐77, this was attenuated by partial stomatal closure. A third organosilicone, ‘Silwet L‐7607’, and two conventional surfactants, ‘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 from 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.