Oxime derivatives of the formula (I) ##STR1## wherein n is 0, 1 or 2 and m is 0 or 1, and Ar is a phenyl radical ##STR2## a naphthyl radical substituted by R.sub.2 and R.sub.3, a 5- to 10-membered heterocyclic radical which contains not more than 3 identical or different heteroatoms N, O and/or S and which is substituted by R.sub.2, R.sub.3 and R.sub.4 and can be substituted by oxo or thiono, or if m is 0, Ar is a radical R--CO, wherein R is a radical --OR.sub.5, in which R.sub.5 is an aliphatic group containing not more than 8 carbon atoms or is an araliphatic group containing not more than 15 carbon atoms or is a cycloaliphatic or aromatic group, each containing not more than 10 carbon atoms, while the possible substituents of the aromatic radicals or of the cycloaliphatic radical are halogen, --CN, --NO.sub.2, lower alkyl, lower alkoxy, haloalkyl; or R is a radical --NH--CO--NH--R.sub.7 or a radical --N(R.sub.6)(R.sub.7), wherein R.sub.6 is hydrogen or lower alkyl and R.sub.7 is hydrogen or an aliphatic group containing not more than 8 carbon atoms or an araliphatic group containing not more than 15 carbon atoms, or a cycloaliphatic ##STR3## wherein R.sub.9 is hydrogen, a cycloaliphatic, araliphatic or aromatic group which is unsubstituted or mono- or polysubstituted at the ring by CN, NO.sub.2, halogen, lower alkyl, lower alkoxy or haloalkyl, or is lower alkenyl, lower haloalkenyl or lower alkynyl, R.sub.10 is an aliphatic group or a cycloaliphatic, araliphatic or aromatic group which is unsubstituted or mono- or polysubstituted at the ring by CN, NO.sub.2, halogen, lower alkyl, lower alkoxy or haloalkyl, R.sub.11 is hydrogen, lower alkyl or cycloalkyl, R.sub.12 is lower alkyl or an aromatic group, while Y is O, S SO, SO.sub.2 or ##STR4## and A is C.sub.2 -C.sub.3 alkylene or C.sub.2 -C.sub.3 alkenylene which is unsubstituted or substituted by halogen, CN or lower alkyl and which together with a carbon chain which is unsubstituted or substituted by halogen, CN or lower alkyl can form a fused ring, and Hal is halogen. These compounds are used for protecting plant crops from the action of aggressive agricultural chemicals.