FOLIAR UPTAKE OF ORGANOSILICONE SURFACTANT OLIGOMERS INTO BEAN LEAF IN THE PRESENCE AND ABSENCE OF GLYPHOSATE

The nonionic organosilicone surfactant 'Silwet'(R) L-77(TM) (1, 2 and 5 g litre-1) and [C-14]glyphosate-monoisopropylammonium (10 g litre-1 a.e.), were applied, alone and in combination with each other, to the upper surfaces of leaves of Vicia faba L. plants growing in a controll ed environment. Over 80 % of the glyphosate was taken up within 10 min , in the presence of 5 g litre-1 L-77, with no further uptake over the remaining period. A similar pattern of uptake was observed with 2 g l itre-1 L-77, but only 30 % was taken up initially. In the presence of 1 g litre-1 L-77 initial glyphosate uptake was only 15 %, but uptake c ontinued, subsequently reaching c.25 % after 360 min, this behaviour b eing essentially the same as that of glyphosate when applied without s urfactant. The uptake of L-77 was not significantly affected by the ad dition of glyphosate, being c.80 % within 10 min at 5 g litre-1, but w ith a slow, further increase of c. 12 %. At 2 g litre-1 uptake was c.4 5 % within 10 min, rising to c.70 % by 360 min. The 1 g litre-1 soluti ons showed a similar pattern, with uptake increasing from c.35 % at 10 min to over 60 % after 360 min. In the absence of glyphosate, individ ual L-77 oligomers penetrated at similar rates. In the presence of gly phosate, however, some discrimination was evident among the oligomers, in particular when the surfactant was added at 1 g litre-1. Literatur e on the foliar uptake of surfactants is reviewed and discussed in rel ation to the results of this study.