The addition of the organosilicone surfactant ‘Silwet L77’ at 1-5 ml litre−1 to formulated glyphosate gave complete surface wetting on application to the adaxial leaf surface of perennial ryegrass (Lolium perenne L.). The wetting characteristics of the solution were associated with rapid foliar uptake and near maximal uptake in 3 h compared to greater than 5 h in the absence of ‘Silwet L77’. Evidence is presented showing that solutions containing ‘Silwet L77’ rapidly infiltrate stomata. Rapid uptake did not occur after application to the astomatous abaxial surface of perennial ryegrass leaves.

The rapid rate of glyphosate uptake reduced the critical rainfall period to 2 h or less, compared to up to 10 h in the absence of ‘Silwet L77’. The use of ‘Silwet L77’ has major practical implications for the use of glyphosate in regions with unpredictable rainfall or high rainfall frequency.