Adjuvants and Herbicide Dose-Reduction Approaches for Enhancing Weed Control in Oil Palm Plantations: Evidence and Research Priorities

Abstract

Effective weed management in oil palm (Elaeis guineensis) plantations depends heavily on herbicides, but tropical rainfall, dense canopies, hard spray water, and waxy weed surfaces can reduce spray retention, absorption, and translocation. This review synthesises mechanistic and field evidence on herbicide adjuvants, including surfactants, and commercial herbicide dose-reduction approaches relevant to oil palm and comparable tropical perennial systems. Adjuvants improve spray characteristics or biological performance, while surfactants are a major adjuvant subclass that enhances wetting, spreading, and cuticular contact. Field studies report improved control of difficult weeds, including Alocasia species, and related approaches are being evaluated against Eleusine indica and other resistant plantation weeds. Commercial herbicide dose-reduction products, including WEED Solut-ioN® as a product marketed by its manufacturer as a “reductant”, have shown potential to maintain acceptable weed control at reduced herbicide rates under selected conditions. However, the evidence remains geographically concentrated and partly dependent on manufacturer documentation, requiring independently replicated multi-site validation. Appropriate additive use may reduce chemical inputs and off-target losses while supporting broader Environmental, Social and Governance (ESG) objectives and relevant United Nations Sustainable Development Goals (SDGs); MSPO and RSPO remain relevant where certification-specific compliance is directly concerned. Priority research includes multi-environment validation of dose-reduction products, life-cycle and ecotoxicological assessment of bio-based formulations, herbicide–additive compatibility under tropical conditions, and practical decision-support tools. Overall, additive-assisted herbicide application is promising when product selection is evidence-based and matched to herbicide chemistry, weed biology, water quality, and field conditions.