Methylene dithiocyanate is primarily used as a biocide in water treatment systems, particularly in cooling towers, industrial water systems, and oilfield operations. It effectively controls the growth of bacteria, algae, and fungi, preventing biofouling and maintaining system efficiency. Its application helps reduce the risk of microbial-induced corrosion, which can damage equipment and pipelines. Additionally, it is utilized in some agricultural settings as a fungicide to protect crops from fungal infections. However, its use requires careful handling and adherence to safety guidelines due to its toxic nature.