A method of controlling pollen formation in a hermaphrodite plant, the method comprising applying to the plant, to seed of the plant or to the locus surrounding the plant or seed, a compound of formula: ##STR1## wherein R.sup.1 is hydrogen or alkyl, R.sup.2 is hydrogen, alkyl, alkyl substituted with up to three halogens (e.g. trichloro- or trifluoro-methyl), cycloalkyl, alkoxyalkyl (e.g. 2-methoxy-ethyl), substituted or unsubstituted aryl or aralkyl or an alkali metal (e.g. sodium or potassium), alkaline earth metal or quaternary ammonium cation, R.sup.3 is halogen, nitro, alkyl, alkyl substituted with up to three halogens (e.g. trichloro- or trifluoro-methyl), cycloalkyl, alkoxy, alkylthio, amino, acylamino (e.g. acetylamino), mono- or di-alkylamino, acyl (e.g. acetyl), haloacyl (e.g. bromoacetyl), cyano, amido, hydroxy, carboxy, alkoxycarbonyl (e.g. methoxycarbonyl) or phenoxy, n is 0 or an integer of 1 to 5 (preferably 0, 1, 2 or 3) and each of X and Y, which may be the same or different, is oxygen or sulphur.