The invention concerns a method of controlling weeds in rice crops, the method being characterized in that one or more compounds of the formula (I), in which R1 is an acyl group selected from the series CO-R?2, CS-R2, CO-OR3, CS-OR3, CO-SR4, CS-SR4, CO-NR5R6¿ and CS-NR?5R6, and R2, R3, R4, R5 and R6¿ and X, Y and Z compounds, are defined as in formula (I) in claim 1, or the salts of such compounds, are applied to the area containing the weeds and rice plants or their seeds, in an effective amount from 0.0001 to 0,5 kg of active ingredient/hectare. These compounds (I) are per se prior art. The invention also concerns, however, the salts of the compounds (I), which are novel.