Pyridine-N-oxide-substituted salicylaldehyde and salicylic acid derivatives of the general formula I ##STR1## where R is a formyl group, a CO.sub.2 H group or a radical which can be hydrolyzed to CO.sub.2 H and the other substituents have the following meanings:R.sup.2 is halogen, alkyl, haloalkyl, alkoxy, haloalkoxy or alkylthio;X is nitrogen or CR.sup.13, R.sup.13 being hydrogen or halogen or together with R.sup.3 forming a 3- to 4-membered alkylene or alkenylene chain in which at least one methylene group is replaced by oxygen;R.sup.3 is halogen, alkyl, haloalkyl, alkoxy, haloalkoxy or alkylthio, or R.sup.3 is linked with R.sup.13 as indicated above to give a 5- or 6-membered ring;Y is oxygen or sulfur;R.sup.14 -R.sup.17 are an unsubstituted or alkyl-substituted cycloalkyl group; an unsubstituted or substituted alkyl group; an unsubstituted or substituted alkoxy or alkylthio group; a dialkylamino group or a dialkylaminoxy group; an unsubstituted or substituted alkenyl or alkynyl group, hydrogen, halogen, nitro or cyano,are described.