The present invention has an excellent effect on emission type multidrug resistant plant disease, the following formula (1):Problem to be solved: to provide a method of controlling the discharge type multiple resistant plant disease including the process of treating the effective amount of the pyridazine compound to the soil which plants plants or plants.本願発明は、排出型多剤耐性植物病害に対する優れた効力を有する、下記式(1):で表されるピリダジン化合物の有効量を植物または植物を栽培する土壌に処理する工程を含む、排出型多剤耐性植物病害の防除方法を提供する。