ABSTRACT
The initial rate of uptake of glyphosate [N(phosphonomethyl)glycine] by the stomatous, adaxial surface of perennial ryegrass (Lolium perenne L.) was enhanced by addition of 0.1% (v/v) Silwet® L-77. Entry of solution into the leaf was initially via open stomata and associated with the low surface tension of the solution containing Silwet L-77 (<30 mN m−1).
In other species, notably dallisgrass (Paspalum dilatatum Poiret.) and quackgrass (Elytrigia repens Beauv.), addition of Silwet L-77 did not enhance uptake of glyphosate and was usually antagonistic.
The species-specific differences were not attributed to differences in stomatal frequency or major leaf surface characteristics. The rate of droplet drying may be enhanced on planar leaf surfaces such as P. dilatatum, and this could be a contributing factor in the development of antagonism. Addition of 3 to 6% (v/v) glycerin as an humectant to solutions containing Silwet L-77 overcame tolerance and resulted in considerable enhancement of glyphosate uptake.
