Importance of adjuvant formulation properties in predicting wetting on leaf surfaces

Abstract

BACKGROUNDLeaf wettability can be a barrier to retention of agrichemical sprays. Adjuvants are used to modify leaf wetting by sprays to enhance retention. A previous study developed a model that accurately predicted nonadjuvant formulation wetting (contact angle) on both synthetic and leaf surfaces. Model inputs were the surface properties, roughness and polarity, as measured by the wetting tension dielectric method, coupled with the formulation properties, surface tension and dielectric constant. Preliminary work has indicated that the wetting ability of adjuvant formulations on different surfaces could be modelled in a similar way if the effect of adjuvants on solution polarity could be accurately quantified.RESULTSThe wetting of nine agrichemical adjuvants, at a range of concentrations, were measured on seven synthetic and 14 leaf surfaces. A novel method was developed to quantify the interfacial dielectric polarity (IDP) of adjuvant formulations. Adjuvant concentration did not change the IDP indicating the surface‐active surfactant molecules migrate to the interface, loading until saturation. Formulation properties of surface tension and IDP were found to be strong predictors of wetting in conjunction with surface properties of the substrate. The previously developed unaltered comprehensive wetting model could predict the wetting of adjuvant formulations on synthetic and leaf surfaces (R2 = 0.9) using these inputs.CONCLUSIONSWetting of adjuvant formulations can be modelled for a wide range of surfaces and this model is expected to advance the selection, and development, of adjuvants to target specific surfaces generating the desired wetting outcome. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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“…117 As such, leaf surface wettability is of utmost importance as it is the preceding step to the leaf adhesion of the respective droplets, as well as their spreading, and retention on the leaf. 118 The tomato leaf, used as a model in this work, presents a characteristic high water contact angle of 118 ± 4° which prevents its wetting (see Fig. 4E).…”

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“…33 Research indicates that vegetable oil, polymers, and non-ionic surfactants significantly boost spray deposition and anti-drift performance. [34][35][36] Most existing studies focus on adjuvant with single component, with limited research on combined adjuvant with multiple chemical components and the effect of downwash airflow on spraying. Comprehensive research on the influence of adjuvants on the physicochemical properties of the liquid, spraying characteristics, spray drift, canopy spray deposition, and control efficacy in UAV applications remains scarce.…”

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“…The authors concluded that the properties of the leaf surface were more important than the formulations. In a follow‐up paper Nairn & Forster 3 studied the wetting of a range of adjuvant formulations and found that the previously developed wetting model was also able to predict the wetting of adjuvant formulations ( R 2 = 0.90) using a novel method to quantify the interfacial dielectric polarity, one of the input parameters required to run the model. It is expected that the wetting model will allow, for example, formulation chemists to better select adjuvants to obtain formulations with the desired wetting outcomes.…”