A compound of Formula: or an agronomically acceptable salt thereof, wherein:- X is O or S; A 1a and A 1b are independently selected from CH and N, wherein A 1a and A 1b are not both CH; A 2 is N; A 3 is CR 4; A 4 is CR 5; R 1 is selected from the group consisting of C 1 -C 6 alkyl, C 1 -C 6 haloalkyl and C 1 -C 6 alkoxy-C 1 -C 3 alkyl; R 2 is selected from the group consisting of hydrogen, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 3 alkoxy-C 1 -C 3 alkyl, C 1 -C 3 alkoxy-C 2 -C 3 alkoxy-C 1 -C 3 -alkyl, C 1 -C 3 haloalkoxy-C 1 -C 3 -alkyl, (C 1 -C 3 alkylsulfonyl-C 1 -C 3 alkylamino)-C 1 -C 3 alkyl, (C 1 -C 3 alkylsulfonyl-C 3 -C 4 cycloalkylamino)-C 1 -C 3 alkyl, C 1 -C 6 alkylcarbonyl-C 1 -C 3 alkyl, C 3 -C 6 cycloalkyl-C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 2 -C 6 -alkenyl, C 2 -C 6 -haloalkenyl, cyano-C 1 -C 6 -alkyl, arylcarbonyl-C 1 -C 3 -alkyl, aryl-C 1 -C 6 alkyl, aryloxy-C 1 -C 6 alkyl (wherein said aryl groups may be optionally substituted with one or more substituents from the group consisting of halogen, C 1 -C 3 -alkoxy, C 1 -C 3 -alkyl, C 1 -C 3 haloalkyl), and a three- to ten-membered mono- or bicyclic ring system, which may be aromatic, saturated or partially saturated and can contain from 1 to 4 heteroatoms each independently selected from the group consisting of nitrogen, oxygen and sulphur the ring system being optionally substituted by one or more substituents selected from the group consisting of nitro, cyano, halogen, C 1 -C 3 alkyl, C 1 -C 3 haloalkyl, C 2 -C 3 alkenyl, C 2 -C 3 alkynyl, C 1 -C 3 alkoxy, C 1 -C 3 haloalkoxy, C 1 -C 6 alkyl-S p- and C 1 -C 6 haloalkyl-S p-; R 4 is selected from the group consisting of hydrogen, hydroxyl, halogen, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 6 alkoxy-C 1 -C 6 alkyl, C 1 -C 6 haloalkoxy-C 1 -C 6 alkyl, C 1 -C 6 alkoxy-C 1 -C 6 alkoxy-C 1 -C 6 alkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkoxy-C 2 -C 6 alkoxy, C 1 -C 6 alkylamino, C 1 -C 6 dialkylamino-, cyano, C 1 -C 6 alkyl-S p- and C 1 -C 6 haloalkyl-S p-; R 5 is selected from the group consisting of hydrogen, hydroxyl, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl and C 1 -C 6 alkoxy-C 1 -C 3 alkyl; and p = 0, 1 or 2. X is O or S; A 1a and A 1b are independently selected from CH and N, wherein A 1a and A 1b are not both CH; A 2 is N; A 3 is CR 4; A 4 is CR 5; R 1 is selected from the group consisting of C 1 -C 6 alkyl, C 1 -C 6 haloalkyl and C 1 -C 6 alkoxy-C 1 -C 3 alkyl; R 2 is selected from the group consisting of hydrogen, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 3 alkoxy-C 1 -C 3 alkyl, C 1 -C 3 alkoxy-C 2 -C 3 alkoxy-C 1 -C 3 -alkyl, C 1 -C 3 haloalkoxy-C 1 -C 3 -alkyl, (C 1 -C 3 alkylsulfonyl-C 1 -C 3 alkylamino)-C 1 -C 3 alkyl, (C 1 -C 3 alkylsulfonyl-C 3 -C 4 cycloalkylamino)-C 1 -C 3 alkyl, C 1 -C 6 alkylcarbonyl-C 1 -C 3 alkyl, C 3 -C 6 cycloalkyl-C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 2 -C 6 -alkenyl, C 2 -C 6 -haloalkenyl, cyano-C 1 -C 6 -alkyl, arylcarbonyl-C 1 -C 3 -alkyl, aryl-C 1 -C 6 alkyl, aryloxy-C 1 -C 6 alkyl (wherein said aryl groups may be optionally substituted with one or more substituents from the group consisting of halogen, C 1 -C 3 -alkoxy, C 1 -C 3 -alkyl, C 1 -C 3 haloalkyl), and a three- to ten-membered mono- or bicyclic ring system, which may be aromatic, saturated or partially saturated and can contain from 1 to 4 heteroatoms each independently selected from the group consisting of nitrogen, oxygen and sulphur the ring system being optionally substituted by one or more substituents selected from the group consisting of nitro, cyano, halogen, C 1 -C 3 alkyl, C 1 -C 3 haloalkyl, C 2 -C 3 alkenyl, C 2 -C 3 alkynyl, C 1 -C 3 alkoxy, C 1 -C 3 haloalkoxy, C 1 -C 6 alkyl-S p- and C 1 -C 6 haloalkyl-S p-; R 4 is selected from the group consisting of hydrogen, hydroxyl, halogen, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 1 -C 6 alkoxy-C 1 -C 6 alkyl, C 1 -C 6 haloalkoxy-C 1 -C 6 alkyl, C 1 -C 6 alkoxy-C 1 -C 6 alkoxy-C 1 -C 6 alkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkoxy-C 2 -C 6 alkoxy, C 1 -C 6 alkylamino, C 1 -C 6 dialkylamino-, cyano, C 1 -C 6 alkyl-S p- and C 1 -C 6 haloalkyl-S p-; R 5 is selected from the group consisting of hydrogen, hydroxyl, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl and C 1 -C 6 alkoxy-C 1 -C 3 alkyl; and p = 0, 1 or 2.