The present invention relates to a method of controlling weeds in a crop field, the method including treating the crop field with crystal of flumioxazin described in the specification, before sowing or planting, at the same time of sowing or planting, or after sowing or planting crop seeds or vegetative organs such as tubers, bulbs, or stem fragments which are treated with one or more compounds selected from the following group B Group B: neonicotinoid type compounds, diamide type compounds, carbamate type compounds, organic phosphorous type compounds, biological nematicidal compounds, other insecticidal compounds and nematicidal compounds, azole type compounds, strobilurin type compounds, metalaxyl type compounds, SDHI compounds, and other fungicidal compounds and plant growth regulators.According to the method of controlling pests of the present invention, weeds in clop fields can be efficiently controlled.
