Provided is a method which exerts an excellent effect in controlling a pest in a field of cotton, using a neonicotinoid compound, an azole compound, a strobilurin compound, and/or a metalaxyl compound, and a PPO inhibiting compound. A method of controlling a pest (a weed, a harmful arthropod, and/or a plant pathogen) in a field of cotton, including treating a field before, at or after seeding with a seed of cotton treated with one or more compounds selected from the group consisting of a neonicotinoid compound, an azole compound, a strobilurin compound and a metalaxyl compound, with one or more PPO-inhibiting compounds selected from the group consisting of flumioxazin, sulfentrazone, saflufenacil, oxyfluorfen, fomesafen and a compound of the formula:
