Novel 1-aryl-4-nitro-pyrazoles which exhibit herbicidal and plant growth-regulating activity of the formula ##STR1## in which R.sup.1 represents in each case optionally substituted alkyl, alkenyl, alkinyl or cycloalkyl andR.sup.2 represents hydrogen, or represents in each case optionally substituted alkyl, alkenyl, alkinyl or cycloalkyl, or represents a radical ##STR2## or R.sup.1 and R.sup.2, together with the nitrogen atom to which they are bonded, represent a saturated heterocyclic radical, which can optionally contain further hetero atoms, andAr represents in each case optionally substituted phenyl or pyridyl,whereinX represents oxygen or sulphur andR.sup.3 represents hydrogen, alkyl, alkoxy, alkoxy-alkyl, alkylthio, alkylthioalkyl, alkylamino, di-alkylamino, halogenoalkyl, alkenyl or alkinyl, or represents optionally substituted cycloalkyl, or represents optionally substituted aryl, or represents optionally substituted aryloxy, or represents optionally substituted arylthio, or represents optionally substituted arylamino,but wherein R.sup.2 only represents hydrogen or a radical ##STR3## if R.sup.1 does not simultaneously represent unsubstituted alkyl or represent alkyl which is substituted by an alkoximino radical.