Hetaroyl derivatives of the formula I where: R1 and R2 are each hydrogen, nitro, halogen, cyano, thiocyanato, hydroxyl, mercapto, C1-C6-alkyl, C1-C6-alkoxy, C1-C6-alkylthio, C1-C6-alkylsulfinyl, C1-C6-alkylsulfonyl or C1-C6-alkoxysulfonyl, where the last 6 radicals may be substituted and/or functionalized; phenyl, phenoxy, phenylthio, phenylsulfinyl or phenylsulfonyl, where the last 5 radicals may be substituted; Z is an unsubstituted or substituted four-membered unsaturated, partially or fully saturated chain consisting of three carbons and one nitrogen; Q is unsubstituted or substituted hydroxypyrazole linked at position 4; and their agriculturally useful salts. A process for preparing the hetaroyl derivatives, compositions comprising them, and the use of these derivatives or these compositions comprising them for controlling undesirable plants.