Copper oxychloride retention and permeation on plant leaves enhanced by pilot-scale biosurfactant extract

This study evaluates the influence of a biosurfactant (BS) extract, obtained at pilot scale from corn steep liquor (CSL), on the formulation of a biopesticide based on copper oxychloride (Cu-Oxy). The retention, permanence, distribution, and partial permeation of copper ions on the surface of tomato and citrus leaves sprayed with the biopesticide Cu-Oxy prepared in BS extract was evaluated in comparison to Cu-Oxy formulation prepared in ultrapure water as a control test. No previous studies have been conducted using a BS extract from CSL as a natural ingredient in a biopesticide formulation for its direct application on real crop leaves. It was observed that the addition of BS (1.6 g/L) to Cu-Oxy made the leaves more wettable, reducing the contact angle by approximately 12% in tomato and citrus leaves. The retention of copper on the adaxial leaf surfaces increased by two to five times compared to the control trials (Cu-Oxy in ultrapure water). The permanence of the active ingredient on leaves, after a washing step, was around 96–98% in the presence of BS and only 61–63% in its absence, which suggests a higher rain fastness and a potential reduction in the number of pesticide applications after rainfall periods. Furthermore, chemical surface analysis showed a more abundant and uniform distribution of copper ions in the presence of the BS extract, which could explain the increase of Cu permeation through the leaf cuticle observed by scanning electron microscopy. Based on these results, it can be concluded that the BS extract from CSL could be a natural ingredient in the formulation of more sustainable agrochemicals, with the objective of reducing the dose of harmful active ingredients and promoting green agriculture.