Survey of herbicide-resistant weed management in oil palm estates from Peninsular Malaysia and Indonesia

Background: The use of herbicides is a common practice to control weeds in oil palm plantation. However, high dependency on herbicides causes intense selection pressure, which could lead to the evolution of herbicide resistance in weed. Objective: To assess planters’ understanding of herbicide resistance management practices. Methods: Data were gathered via the application of questionnaires during the 2022 growing season to planters working with oil palm in Peninsular Malaysia and Indonesia. There were 101 respondents, covering about 14 states. Results: Planters (75 to 85% respondents) found herbicide rotation, cover crops, and pre-emergence herbicide application effective against herbicide-resistant weeds, but high herbicide costs hindered their selection of chemical solutions. Peninsular Malaysia planters (30 to 78% respondents) reported five major putative resistant weeds such as Eleusine indica (L.) Gaertn., Clidemia hirta (L.) D. Don., Melastoma malabathricum (L.), Ischaemum muticum (L.), and Asystasia gangetica (L.) T. Anderson. Indonesian planters (28 to 43% respondents) faced putative resistance in E. indica and C. hirta. Peninsular Malaysia's higher incidence of putative resistance was linked to insufficient knowledge of herbicide classification, less use of tank-mixed herbicides, and reduced herbicide rates, potentially fostering resistance evolution. Conclusions: The survey revealed that Indonesia planters possess a better understanding of herbicide resistance management as compared to Peninsular Malaysia planters. There is a need to increase awareness on sustainable use of herbicides through training and educational programs for planters in Peninsular Malaysia.