EFFECTS OF TETRAETHYLENEGLYCOL MONOOCTYLETHER (C8E4) ON MOBILITIES OFSELECTED PESTICIDES IN CITRUS LEAF CUTICLES

Permeabilities of cuticles determine rates of foliar uptake of pestici des. Permeability is proportional to solute mobility and differential solubility in cuticles and permeability can be increased by certain ad juvants called accelerators. Tetraethylene glycol monooctylether (C8E4 ) is an accelerator. We have measured solute mobilities in Citrus leaf cuticular membranes (CM) in absence (k(pls)) and presence (k(C8E4)*) Of C8E4 sorbed in CM. Average concentrations of C8E4 in cuticles and cuticular waxes amounted to 8.6 and 0.86 %, respectively. Mobilities i n native CM (k(pls),) decreased with increasing molar volumes (V-x) o f solutes and a plot-log k(pls) vs. V-x was linear (r(2) = 0.96). C8E 4 increased solute mobility by up to 136-fold. This surfactant effect increased with molar volume of solutes and an excellent linear relatio nship between surfactant effect on mobility and molar volume of five c yclic solutes (2,4-D, NAA, triadimenol, tebuconazol, bitertanol) was o bserved (r(2) = 0.99), while effects on mobilities of aliphatic acids were much lower as compared to cyclic compounds of comparable size. Th us, differences in solute mobilities in cuticles caused by differences in solute size were greatly reduced by C8E4. This has practical impli cations, because in the presence of suitable accelerators, rates of fo liar uptake of pesticides differing in size are much higher and more u niform than in absence of accelerators.