Abstract: The present invention provides a disinfectant comprising as an active ingredient maleic acid and/or maleic anhydride.

Abstract: An environmentally-safe method for protecting plants is provided for reducing the use of chemically-synthesized pesticide. Specifically, an anti-microbial and/or anti-viral composition comprising a laccase, a cell of a laccase-producing microorganism or a treated product thereof, and one or more kinds of phenol derivatives each represented by the general formula (I) shown below or a salt of the phenol derivative is provided. Furthermore, a plant disease-preventing agent, seed-sterilizing agent, post-harvest agent, and nutrient solution-sterilizing agent, each containing the composition; and plant disease-preventing method, seed-sterilizing method, post-harvest-treatment method, and nutrient solution-sterilizing method in hydroponics and solid-medium hydroponics using each f the agents are provided.