PROBLEM TO BE SOLVED: To effectively control or exterminate disease injury and various algae without damaging laver. SOLUTION: This treating agent is obtained by formulating 5-90 wt.% of at least either one of lactic acid and acetic acid, 0.1-10 wt.% of a 6-14C saturated fatty acid such as caprylic acid or pelargonic acid, its ester or its salt, 1-50 wt.% of propylene glycol, etc., as a dissolution aid for the saturated fatty acid and, as necessary, water and an organic acid other than the lactic acid and acetic acid and an inorganic acid as a pH adjustor. The treating agent is diluted with water or seawater so that the sum total of the lactic acid and acetic acid is 0.01-1.8% and the sum total of the saturated fatty acid, its ester or its salt is 0.0005-0.1%. Thereby, a treating liquid is obtained. A laver or a culture tool such as a laver net to which the laver sticks is dipped in the resultant treating liquid or the treating liquid is passed therethrough to bring the laver into contact with the treating liquid.
