PROBLEM TO BE SOLVED: To obtain a plant growth regulator facilitating harvesting operation of cotton by defoliating a cotton plant and further promoting cleavage of cotton balls, to provide a method for defoliating the cotton and a method for promoting the cleavage of the cotton balls. SOLUTION: This plant growth regulator for harvesting the cotton comprises a compound (I) represented by formula (I) [wherein, X denotes a group CH or nitrogen atom; Z denotes a halogen atom; A denotes oxygen atom, or the like; R<1> denotes hydroxy group, a 1-7C a alkoxy group, or the like; R<2> denotes hydrogen atom or methyl group; and R<3> denotes hydrogen atom, a halogen atom, a 1-3C alkyl group or a 1-3C alkoxy group] as an active ingredient and has actions on defoliation and promotion of ball cleavage of the cotton.
