The present invention relates to a method of controlling weeds in a crop fields, land under perennial crops, or a non-crop land, the method comprising applying an effective amount of crystal of flumioxazin which is one or more selected from the group consisting of 1st crystal, 2nd crystal, 3rd crystal, 4th crystal, 5th crystal, 6th crystal and 7th crystal, each of the crystals showing a powder X-Ray diffraction pattern which has diffraction peaks with 2θ values (°) shown in the corresponding right column of Table 1 of the Specification, to soil where the weeds are grown or to be grown, or weeds. According to the present invention, a wide range of weeds can be controlled in a crop field, land under perennial crops, or a non-crop land.
