Herbicide controlled release formulations (CRFs) are designed to reduce undesired herbicide leaching and increase the herbicide concentration at the top of the soil for reduced soil and water contamination and improved herbicidal activity. In the current study we developed novel CRFs for the anionic herbicide imazapyr (IMP) based on its binding to poly dimethyldiallylammonium chloride (PDADMAC)-montmorillonite composites. Polycation adsorption on the clay was rapid and reached a high loading of 0.9 g/g which results in charge reversal of the surface. Fourier transform infrared and X-ray diffraction of the composites indicated electrostatic interaction between the polycation and the surface, intercalation of the polycation in the clay and formation of loops and tails on the surface at high polycation loadings. Such a configuration, in comparison to a train configuration, creates available positive binding sites resulting in high IMP binding. However, IMP binding to the composites was found to be affected not only by polycation configuration but also by composite flocculation. Upon adding high concentrations of IMP to a PDADMAC-montmorillonite composite (0.16 g polymer/g clay) a high herbicide loadings was reached (66% active ingredient). Testing IMP release from formulations applied on a thin layer of soil demonstrated that its release from PDADMAC-montmorillonite formulations was substantially slower than its release from the commercial formulation. The ability of the newly designed formulations to decrease leaching while maintaining good herbicidal activity was demonstrated by applying a soil column bioassay.