Non-therapeutic use of compounds of formula I wherein R 1 is selected from O and NH; R 2 is selected from CH and N; R 3 is selected from halogen, C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl, C 1 -C 2 -monohaloalkyl, C 1 -C 2 -dihaloalkyl, monohalo-ethenyl, dihalo-ethenyl, C 3 -C 6 -cycloalkyl and -O-C 1 -C 4 -alkyl; R 4 is selected from C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl, -C(=O)-C 1 -C 2 -alkyl, C 1 -C 4 -haloalkyl, C 2 -C 4 -haloalkenyl, -(C 1 -C 2 -alkyl)-O-(C 1 -C 2 -alkyl) and -CH 2 -cyclopropyl; R a is selected from halogen, CN, -NR 5 R 6, C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl, C 2 -C 4 -alkynyl, -O-C 1 -C 4 -alkyl, -C(=N-O-C 1 -C 4 -alkyl)-C 1 -C 4 -alkyl, -C(=O)-C 1 -C 4 -alkyl, -O-CH 2 -C(=N-O-C 1 -C 4 -alkyl)-C 1 -C 4 -alkyl, C 3 -C 6 -cycloalkyl, C 3 -C 6 -cycloalkenyl, -C 1 -C 2 -alkyl-C 3 -C 6 -cycloalkyl, -O-C 3 -C 6 -cycloalkyl, phenyl, 3- to 6-membered heterocycloalkyl, 3- to 6-membered heterocycloalkenyl and 5- or 6-membered heteroaryl, wherein said heterocycloalkyl, heterocycloalkenyl and heteroaryl besides carbon atoms contain 1, 2 or 3 heteroatoms selected from N, O and S, wherein said phenyl, heterocycloalkyl, heterocycloalkenyl and heteroaryl are bound directly or via an oxygen atom or via a C 1 -C 2 -alkylene linker, and wherein the aliphatic and cyclic moieties of R a are unsubstituted or carry 1, 2, 3, 4 or up to the maximum number of identical or different groups R b: R b is selected from halogen, CN, NH 2, NO 2, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, -O-C 1 -C 4 -alkyl, and -O-C 1 -C 4 -haloalkyl; R 5, R 6 are independently of each other selected from the group consisting of H, C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl and C 2 -C 4 -alkynyl; n is an integer selected from 0, 1, 2 and 3; and in form or stereoisomers and tautomers thereof, and the N-oxides and the agriculturally acceptable salts thereof, for combating phytopathogenic fungi containing an amino acid substitution F129L in the mitochondrial cytochrome b protein conferring resistance to Qo inhibitors. R 1 is selected from O and NH; R 2 is selected from CH and N; R 3 is selected from halogen, C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl, C 1 -C 2 -monohaloalkyl, C 1 -C 2 -dihaloalkyl, monohalo-ethenyl, dihalo-ethenyl, C 3 -C 6 -cycloalkyl and -O-C 1 -C 4 -alkyl; R 4 is selected from C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl, -C(=O)-C 1 -C 2 -alkyl, C 1 -C 4 -haloalkyl, C 2 -C 4 -haloalkenyl, -(C 1 -C 2 -alkyl)-O-(C 1 -C 2 -alkyl) and -CH 2 -cyclopropyl; R a is selected from halogen, CN, -NR 5 R 6, C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl, C 2 -C 4 -alkynyl, -O-C 1 -C 4 -alkyl, -C(=N-O-C 1 -C 4 -alkyl)-C 1 -C 4 -alkyl, -C(=O)-C 1 -C 4 -alkyl, -O-CH 2 -C(=N-O-C 1 -C 4 -alkyl)-C 1 -C 4 -alkyl, C 3 -C 6 -cycloalkyl, C 3 -C 6 -cycloalkenyl, -C 1 -C 2 -alkyl-C 3 -C 6 -cycloalkyl, -O-C 3 -C 6 -cycloalkyl, phenyl, 3- to 6-membered heterocycloalkyl, 3- to 6-membered heterocycloalkenyl and 5- or 6-membered heteroaryl, wherein said heterocycloalkyl, heterocycloalkenyl and heteroaryl besides carbon atoms contain 1, 2 or 3 heteroatoms selected from N, O and S, wherein said phenyl, heterocycloalkyl, heterocycloalkenyl and heteroaryl are bound directly or via an oxygen atom or via a C 1 -C 2 -alkylene linker, and wherein the aliphatic and cyclic moieties of R a are unsubstituted or carry 1, 2, 3, 4 or up to the maximum number of identical or different groups R b: R b is selected from halogen, CN, NH 2, NO 2, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, -O-C 1 -C 4 -alkyl, and -O-C 1 -C 4 -haloalkyl; R 5, R 6 are independently of each other selected from the group consisting of H, C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl and C 2 -C 4 -alkynyl; wherein said heterocycloalkyl, heterocycloalkenyl and heteroaryl besides carbon atoms contain 1, 2 or 3 heteroatoms selected from N, O and S, wherein said phenyl, heterocycloalkyl, heterocycloalkenyl and heteroaryl are bound directly or via an oxygen atom or via a C 1 -C 2 -alkylene linker, and wherein the aliphatic and cyclic moieties of R a are unsubstituted or carry 1, 2, 3, 4 or up to the maximum number of identical or different groups R b: R b is selected from halogen, CN, NH 2, NO 2, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, -O-C 1 -C 4 -alkyl, and -O-C 1 -C 4 -haloalkyl; R 5, R 6 are independently of each other selected from the group consisting of H, C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl and C 2 -C 4 -alkynyl; R b is selected from halogen, CN, NH 2, NO 2, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, -O-C 1 -C 4 -alkyl, and -O-C 1 -C 4 -haloalkyl; R 5, R 6 are independently of each other selected from the group consisting of H, C 1 -C 6 -alkyl, C 1 -C 6 -haloalkyl and C 2 -C 4 -alkynyl; n is an integer selected from 0, 1, 2 and 3;