Helping farmers to reduce herbicide environmental impacts
While pesticides help to effectively control crop pests, their collateral effects often harm the environment.On the French island of Reunion in the Indian Ocean, over 75% of the pesticides used are herbicidesand they are regularly detected in water. Agri-environmental models and pesticide risk indicators canbe used to predict and to help pesticide users to reduce environmental impacts. However, while thecomplexity of models often limits their use to the field of research, pesticide risk indicators, which areeasier to implement, do not explicitly identify the technical levers that farmers can act upon to limitsuch transfers on their scale of action (the field). The aim of this article is to contribute to developinga decision support tool to guide farmers in implementing relevant practices regarding the reduction ofpesticide transfers. In this article, we propose a methodology based on classification and regression trees.We applied our methodology to a pesticide risk indicator (I-PHY indicator) for identifying the importanceof the variables, their interactions and relative weight in contributing to the score of the indicator. Weapplied our methodology to the assessment of transfer risks linked to the use of 20 herbicides appliedto all soils in Reunion and according to different climate, plot management and product applicationscenarios (4096 scenarios tested). We constructed regression trees which identified, for each herbicideon each soil type, the contribution made by each input variable to the construction of the indicator score.The tree is represented graphically, and this aids exploration and understanding. The 20 herbicides weredivided into 3 groups that differed through the main contributing variable to the indicator score. Thesevariables were all technical levers available to farmers to limit transfer risks. These trees then becomedecision support tools specific to each pesticide user, enabling them to take appropriate decisions witha view to reducing pesticide environmental impacts.