Influence of surfactant HLB values and commercial agricultural adjuvants on pesticide mimic penetration in plant leaves

BACKGROUND: Effective pesticide action is crucial for optimizing efficacy and minimizing environmental impact, particularly with the increasing reliance on systemic pesticides. Adjuvants, including surfactants are commonly used to enhance penetration, but their performance depends on the physicochemical properties of both the pesticide and the surfactants used in the formulations. This study examines how surfactant hydrophilic-lipophilic balance (HLB) values and commercial adjuvants affect pesticide penetration through plant cuticles. RESULTS: We first assessed the penetration of two fluorescent pesticide mimics, Rhodamine B (hydrophilic) and Nile Red (lipophilic), into spring onion leaves using confocal laser scanning microscopy. On this highly waxy leaf, high HLB surfactants significantly enhanced the penetration of Rhodamine B, while low HLB surfactants promoted Nile Red penetration. Surfactants with intermediate HLB values had minimal effect on either compound. Among seven commercial adjuvants tested, only Squall and Prolong significantly improved the penetration of both pesticide mimics. To evaluate the role of leaf surface properties, we extended adjuvant experiments to sugarbeet and potato leaves, which have higher surface polarity and roughness. On these leaves, both fluorescent pesticide mimic penetrations (in the absence of any additive) were higher, and multiple adjuvants presented enhanced penetration, in contrast to their limited performance on green onion. CONCLUSION: Surfactant polarity plays a key role in overcoming cuticular resistance on waxy, low-polarity leaves like green onion. On more permeable leaves, adjuvant performance is governed by surface characteristics. These findings underscore the importance of tailoring adjuvant selection to both pesticide polarity and crop-specific leaf properties. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.