The invention relates to novel 2-ethyl-4,6-dimethylphenyl-substituted spirocyclic tetramic acid derivatives of the formula (I) ##STR00001## in which A, B and G are as defined above, to a plurality of processes and intermediates for their preparation and to their use as pesticides and/or herbicides, and also to selective herbicidal compositions comprising firstly the 2-ethyl-4,6-dimethylphenyl-substituted spirocyclic tetramic acid derivatives of the formula (I) (where G may also be hydrogen) and secondly at least one crop plant compatibility-improving compound.