In two separate studies, the herbicide cyanazine was microencapsulated within the following polymers: cellulose acetate butyrate (CAB); ethyl cellulose of two different viscosities (EC22 and EC100); low and medium molecular weight poly(methyl methacrylate) (PMML and PMMM); poly(α-methylstyrene) (PMS). Pesticide efficacy studies on five weed species (barnyardgrass, smallflower morningglory, crowfootgrass, Florida beggarweed, and Palmer amaranth) were conducted under greenhouse conditions over a period of 12 weeks for study 1 and 25 weeks for study 2, using the commercial formulation Bladex 90 DF for comparison purposes. In both studies, the poly(α-methylstyrene) formulations were consistently comparable or superior to the commercial formulation in long-term control. Keywords: Cyanazine; ethyl cellulose; formulation; greenhouse; groundwater; herbicide; microcapsule; poly(α-methylstyrene); polymer; weed