The radiolytic degradation of the widely used herbicide dicamba (3,6-dichloro-2-methoxybenzoic acid), employing gamma irradiation in laboratory batch conditions and with a beam of accelerated electrons in flow-through installation, was investigated. The effects of dose magnitude, ozone or hydrogen peroxide in irradiated solution, and scavengers such as nitrate and hydrogen carbonate on the effectiveness of dicamba decomposition and the products formed were investigated. Changes in the toxicity of irradiated solutions were measured with the Microtox and Spirotox toxicity tests. The application of radiolytic degradation was also examined for decomposition of herbicides in commercial agrochemical preparations.