Effect of surfactants and liquid fertilisers on transcuticular penetration f fungicides

Penetration of active compounds into the leaves plays an important role in their systemic activity. The effect of surfactants and liquid fertilisers on the penetration of fungicides was studied in model trials with the cuticle from Bryophyllum calycinum. Solutions of the fungicides were pipetted on pieces of cuticle laid on agar covered by spores of Cladosporium cladosporioides. The diameters of the inhibitory zones were measured and served to gauge the level of penetration by the variants. The size of the inhibitory zone of the control variant of Alto Combi 420 SC pipetted on the cuticle was only reduced to 92.6% of the variant where the solution was pipetted directly onto the agar; thus, the cuticle's effect on penetration was minor. Penetration through the cuticle decreased the diameters of inhibitory zones also of other fungicides: Discus to 84.1%, Horizon 250 E to 83.0%, Baycor 25 WP to 77.7%, Topsin 500 SC to 60.0 and Amistar to 37.8% of their control variant. The high penetration by the original formulations Alto Combi and Discus left no or little room for any increase of their penetration when mixed with additives. A higher penetration by Discus would also be undesirable because of its contact activity. The additives increased penetration most when mixed with Topsin and Amistar. The effect of surfactants and liquid fertilisers on the penetration of fungicides cannot be generalised. It was unique to each fungicide/additive combination. While the conditions of the trials enabled high penetration of some original formulations, the question arises how the additives will perform under conditions that will allow only low penetration.