The present invention provides a plant epidemic prevention agent that allows for easily and efficiently decomposing and eliminating pathogenic germs that cause plant epidemic and effectively suppressing plant disease caused by the pathogenic germs and making diseased plants recover from the disease without adversely affecting the human body and allows for achieving environmental preservation; a plant epidemic prevention method and a plant epidemic prevention system using the plant epidemic prevention agent; plants and a plant cultivation method. The plant epidemic prevention agent contains at least a photocatalytic powder containing phosphorous or an apatite structure. The plant epidemic prevention method includes supplying the plant epidemic prevention agent to plants. The plant epidemic prevention system has at least a monitoring unit and a supplying unit, wherein lesions of a plant are detected by the monitoring unit and the plant epidemic prevention agent is supplied to the diseased plant by the supplying unit.