OBJECTIVES •This study aimed to i) assess the control that ditches exert over water contamination ii) identify the most effective management method (among dredging, mowing, chemical weeding, burning) to maximize the buffer effect iii) evaluate the effect of the spatial distribution of maintenance along the network on the buffer effect. HIGHLIGHTS • We analyzed the sensitivity of ditch pesticide retention to ditch properties derived from field observations, with a new reactive ditch transfer model. • Simulated pesticide retention in a flooded ditch varied from 0.5 to 99%, and ditch properties were a key factor explaining this variability. • A wide ditch, burned or mowed, showed to have a better overall retention capacity. • Ditches networks with high retention capacity reaches in their downstream part have a greater efficiency than when their high retention capacity is located upstream.