Contrasting impacts of mixed nonionic surfactant micelles on plant growth in the delivery of fungicide and herbicide

Hypothesis: Nonionic alkyl ethoxylate surfactants are widely used in agrochemicals to facilitate the per-meation of systemic herbicides and fungicides across the plant waxy film. Industrial grade surfactants are often highly mixed and how the mixing affects their interactions with pesticides and wax films remains largely unexplored. A better understanding could enable design of mixed nonionic surfactants for herbi-cides and fungicides to maximize their efficiency and reduce wastage whilst controlling their impact on plant wax films. Experiment: In this study, nonionic surfactants with general structure n-oxyethylene glycol monododecyl ether (C12En) were used to form surfactant mixtures with the same average ethoxylate numbers but dif-ferent hydrophilic-lipophilic balance (HLB) values. Their mixed micellar systems were then used to sol-ubilize a herbicide diuron (DN) and a fungicide cyprodinil (CP), followed by plant wax solubilization upon contact with wax films. These processes were monitored by H-1 NMR and SANS. Finding: Pesticide solubilization made surfactant micelles effectively more hydrophobic but subsequent wax dissolution caused pesticide release and the restoration of the micellar amphiphilicity. Nonionic surfactants with lower HLBs form larger nanoaggregates, show enhanced wettability, and have better ability to solubilize and permeate pesticides across the wax film, but may cause significant damage to plant growth. These observations help explain why herbicides applied on weeds would benefit from surfactants with lower HLB values while fungicides require surfactants with HLBs to balance between delivery efficiency and potential phytotoxicity risks. (C) 2022 Published by Elsevier Inc.

Automated summary

The study investigates the interaction between mixed nonionic surfactants and pesticides/wax films. Lower HLB nonionic surfactants form larger nanoaggregates, enhancing wettability and solubilization of pesticides across the wax film, while higher HLB surfactants balance delivery efficiency and phytotoxicity risks for fungicides. The findings provide insights for the design of surfactants in agrochemical formulations.