Oil emulsions enhance transcuticular movement of captan in apple leaves

The purpose of this study was to determine whether oil emulsions enhanced penetration of captan, a chloroalkyl thio heterocyclic non-systemic fungicide through apple leaf cuticles. Cuticles from apple leaves were isolated with enzymes and treated with 1% soybean oil emulsified with Latron B-1956® and K1, and two commercial soybean oil emulsions, dormant oil and SunSpray on the outer morphological surface. Where captan and oil were applied together, the percentage of captan that penetrated the cuticle never exceeded 3.5% even under a worst-case scenario but this could be sufficient to cause phytotoxicity. When applied on the outer morphological surface of the cuticle, all oil formulations increased captan penetration by more than 50% over the amount penetrated through control cuticles. The greatest penetration of captan was through cuticles treated with dormant oil. A significant amount of captan (51% over the control amount) penetrated through the inner morphological surface of the cuticle. Captan penetration was more than 40% greater through the abaxial than through the adaxial cuticles. Increasing captan concentration increased captan penetration and a linear relationship existed between captan concentration and captan penetration through the cuticle. The study clearly showed that oil emulsions facilitated penetration of significant amount of captan through the cuticle, which may have serious implications for phytotoxicity of leaves.