PURPOSE: A germination and proliferation inhibitor against microorganisms causing plant diseases that is mainly composed of eugenol, thus controlling not only disease-causative microorganisms at terrestrial parts but also those causing soil diseases with no toxicity and high safety.

CONSTITUTION: Eugenol of the formula, non-toxicity and high safety is used as the major ingredient and is preferably combined with an emulsifier such as propylene glycol, its polymer, sucrose fatty acid ester, sorbitol fatty acid ester and other no-toxicity surfactants for emulsification, or adsorbed on a porous inorganic material with high adsorption such as magnesia, alumina to give the objective inhibitor which can control microorganism causing plant diseases which could not have been controlled with conventional pesticides such as fusarium, phytophthora, cortinium, pythium, rhizoctonia, tomato bacterial wilt and other soil diseases.