Pesticide use in agricultural watersheds leads to an important surface and subsurface water contamination in France. Awaiting a deep evolution of agricultural practices and a sustained decrease in pesticide use, it is of interest to limit transfers form agricultural fields to rivers. A deepen knowledge of processes at stake and their potential interactions is made possible with large field databases, or with physically-based modeling. Physically-based models are built on mechanistic equations and are able to represent the processes and the physics observed on the field if the system is well described. Integrated surface and subsurface hydrologic models (ISSHM) are complex models taking into account the major water pathways and their interctions. Two ISSMH intercomparison studies from Maxwell et al. (2014) and Kollet et al. (2017) show that models such as CATHY (Camporese et al., 2010), HydroGeo-Sphere (Brunner et al., 2012), and Parflow (Kollet 2006) share many common features. Their behaviours in simulation on virtual and real hillslope are coherent. However, they de not use the same surface-subsurface coupling strategies and include solute transport with various complexity levels. The coupling strategy of CATHY is based on the switching boundary conditions regarding to the situation of each surface cell at each time step. It has been proved to be very efficient and able to correctly represent water flow interactions between surface and subsurface (Sulis et al., 2010 ans Guay et al., 2013). Recently, reactive solute transport has been implemented in the CATHY model (Weill et al., 2011 and Gatel et al., 2017submitted). In the present work, the surface-subsurface switching procedure for solutes is improved in order to achieve a better mass conservation, and a mixing module is implemented to represent the solute mobilisation from the top soil to surface runoff. The new coupled model named CATHY-Pesticide is evaluated for an intense rain event on an experimental vineyard hillslope.