Fuente: WIPO "tomato" It is an object of the present invention to provide an agent for inhibiting soil diseases that is capable of effectively inhibiting the onset of soil diseases and is highly safe. The present invention relates to an agent for inhibiting soil diseases comprising S-allylcysteine or a salt thereof. The agent for inhibiting soil diseases according to the present invention preferably further comprises an amino acid or a salt thereof. Soil diseases can be inhibited by applying the agent for inhibiting soil diseases of the present invention to a soil.