Benomyl (also marketed as Benlate) is a fungicide introduced in 1968 by DuPont. It is a systemic benzimidazole fungicide that is selectively toxic to microorganisms and invertebrates, especially earthworms. Benomyl binds to microtubules, interfering with cell functions, such as meiosis and intracellular transportation.The selective toxicity of benomyl as a fungicide is possibly due to its heightened effect on fungal rather than mammalian microtubules.n a laboratory study, dogs fed benomyl in their diets for three months developed no major toxic effects, but did show evidence of altered liver function at the highest dose (150 mg/kg).