The invention relates to the use of piperazine compounds of formula (I) or the agriculturally useful salts of piperazine compounds of formula (I) as herbicides, the variables in formula (I) being defined as cited in the claims and the description.本發明係關於下式I哌化合物或式I哌化合物的農業上可用之鹽作為除草劑之用途,其中式I中之變量係如申請專利範圍及發明說明所定義。