HERBICIDALLY ACTIVE BICYCLIC 1,3-DIONE COMPOUNDS The present invention relates to novel, herbicidally active cyclic diones, and derivatives thereof, to processes for their preparation, to compositions comprising those compounds, and to their use in controlling weeds, especially in crops of useful plants, or in inhibiting plant growth. Cyclic diones having herbicidal action are described, for example, in US 4,175,135 and US 4,209,532. Novel bicyclic diones, and derivatives thereof, having herbicidal and growth-inhibiting properties have now been found. The present invention accordingly relates to compounds of formula I (FORMULA REMOVED) wherein R1 is methyl, ethyl, n-propyl, /so-propyl, cyclopropyl, halomethyl, haloethyl, halogen, vinyl, ethynyl, methoxy, ethoxy, halomethoxy or haloethoxy, R2and R3 are independently hydrogen, halogen, C1-C6alkyl, C1-C6haloalkyl, C1-C6alkoxy, C1- C6haloalkoxy, C2-C6alkenyl, C2-C6haloalkenyl, C2-C6alkynyl, C3-C8alkenyloxy, C3. Cahaloalkenyloxy, C3-C6alkynyloxy, C3-C6cycloalkyl, C1-C6aikylthio, C1-C6alkylsulfinyl, C1- C6alkylsulfonyl, C1-C6alkylsulfonyloxy, C1-C6haloalkylsulfonyloxy, cyano, nitro, optionally substituted phenyl or optionally substituted heteroaryl, where at least one of R2and R3 is optionally substituted phenyl or optionally substituted heteroaryl, R4is hydrogen, methyi, ethyi, n-propyi, /so-propyi, haiomethyi, haioethyi, haiogen, vinyi, ethynyi, methoxy, ethoxy, halomethoxy or haloethoxy, R5 and R6 are independently hydrogen, C1-C6alkyl, C2-C6alkenyl, C2-C6alkynyl, C1-C6haloalkyl, C2-C6haloalkenyl, C1-C6alkoxy, C3-C6alkenyloxy, C3-C6haloalkenyloxy, C3-C6alkynyloxy, C1- C4alkoxyC1-C4alkyl, C1-C4 alkoxy C1-C4 alkoxy, C1-dalkoxyC1-C4alkoxyC1-dalkyl C1-C6alkylthio, C6-Cehaloalkoxy, C1-C4alkoxyC1-C4alkyl, C1-C4alkoxyC1-C4alkoxy, C1-C4alkoxyC1-C4alkoxyC1-C4alkyl, C1-C6alkylthio, C1-C4alkylthioC1-C4alkyl, C1-C4alkylsulfinyl, C1-C4alkylsulfinylC1-C4alkyl, C1-C4alkylsulfonyl, C1-C4alkylsulfonylC1-C4alkyl, halo, cyano, C1-C6cyanoalkyI, C1-C6cyanoalkoxy, hydroxy, C3-C6alkenyloxy, C3-C6haloalkenyloxy, C3-C6alkynyloxy, phenoxy, substituted phenoxy, heteroaryloxy, substituted heteroaryloxy, heterocyclyloxy, substituted C4alkylsulfonylaminoC1-C4alkyl, C1-C4haloalkylsulfonylaminoC1-C4alkyl, phenylsulfonylaminoC1-C4alkyl, substituted phenylsulfonylaminoC1-C4alkyl, tri(C1-C4alkyl)si!yl, tri(C1-C4alkyl)silyloxy, phenyl and substituted phenyl, heteroaryl and substituted heteroaryl, heterocyclyl and substituted heterocyclyl. Preferably, the C6-C3alkylene and C2-C3alkenylene groups X and Y are The latentiating group G is preferably selected from C1-C8alkyl, C2-C8 haloalkyl, phenylC,-C8alkyl (wherein the phenyl may optionally be substituted by C1-dalkyl, CrC3haloalkyl, C1-C3alkoxy, C1-dhaloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), heteroarylC1-C8alkyl (wherein the heteroaryl may optionally be substituted by C1-dalkyl, C1-dhaloalkyl, C1-C3alkoxy, C1-C3 haloalkoxy, C1-C3alkylthio, C1-C3 alkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), C3-C8 alkenyl, C1-d haloalkenyl, C1-d alkynyl, C(Xa)-Ra, C(Xb)-Xc-Rb, C(Xd)-N(Rc)-Rd, -SOrRe, -P(Xe)(Rf)-R9 or CHrXf-Rh wherein Xa, Xb, Xc, Xd, Xe and X* are independently of each other oxygen or sulfur; Ra is H, C1-C18 alkyl, C2-C18alkenyl, C2-C18alkynyl, C1-dohaloalkyl, C1-C10cyanoalkyl, C1-C10nitroalkyl, C1-C10aminoalkyl, C1-CsalkylaminoC1-dalkyl, C2-C8dialkylaminoC1-C5alkyl, C3-CTCycloalkylC1-Csalkyl, C1-dalkoxyC1-dalkyl, C1-dalkenyloxyC1-dalkyl, C1-dalkynyloxyC1-C5alkyl, CrCsalkylthioC1-Csalkyl, C1-dalkylsulfinylC1-dalkyl, C1-dalkylsulfonylC1-dalkyl, Cz-dalkylideneaminoxyC1-dalkyl, C1-dalkylcarbonylC1-dalkyl, C1-dalkoxycarbonylC1-dalkyl, aminocarbonylC1-C5alkyl, C1-C5alkylaminocarbonylC1-C5alkyl, C2-C8dialkylaminocarbonylC1-C5alkyl, C1-dalkylcarbonylaminoC1-dalkyl, /V-C1-dalkylcarbonyl-A/-C1-dalkylaminoC1-dalkyl, C3-C6trialkylsilylC1-C5alkyl, phenylCrC5alkyl (wherein the phenyl may optionally be substituted by C1-C3alkyl, C1-dhaloalkyl, C1-dalkoxy, C1-dhaloalkoxy, C1-C3alkylthio, CrC3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), heteroarylC1-C5alkyl, (wherein the heteroaryl may optionally be substituted by C1-dalkyl, C1-dhaloalkyl, C1-dalkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-dalkylsulfinyl, C1-dalkylsulfonyl, halogen, cyano, or by nitro), C2-C5haloalkenyl, C3-C8cycloalkyl, phenyl or phenyl substituted by C1-dalkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro, heteroaryl or heteroaryl substituted by C1-C3alkyl, C1-dhaloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro, Rb is C1-C18alkyl, C3-C18alkenyl, C3-C18alkynyl, C1-dohaloalkyl, C1-C10cyanoalkyl, C1-donitroalkyl, Crdoaminoalkyl, C1-dalkylaminoC1-dalkyl, C2-C8dialkylaminoC1-C5alkyl, C3-C7cycloalkylC1-C5alkyl, C1-C5alkoxyC1-C5alkyl, C3-C5alkenyloxyC1-C5alkyl, C1-dalkynyloxyC1-C5alkyl, C1-C5alkylthioC1-dalkyl, C1-dalkylsulfinylC1-dalkyl, C1-dalkylsulfonylC1-dalkyl, C2-dalkylideneaminoxyC1-dalkyl, C1-dalkylcarbonylC1-dalkyl, C1-dalkoxycarbonylC1-dalkyl, aminocarbonylC1-dalkyl, C1-dalkylaminocarbonylC1-dalkyl, C2-C8dialkylaminocarbonylC1-dalkyl, C1-dalkylcarbonylaminoC1-dalkyl, /V-C1-dalkylcarbonyl-W-C1-dalkylaminoC1-dalkyl, CrCstrialkylsilylC1-Csalkyl, phenylC1-C5alkyl (wherein the phenyl may optionally be substituted by C1-dalkyl, C1-C3haloalkyl, CrC3alkoxy, C1-dhaloalkoxy, CrC3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), heteroarylC1-dalkyl, (wherein the heteroaryl may optionally be substituted by C1-C3alkyl, C1-dhaloalkyl, C1-dalkoxy, C1-dhaloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), C3-C5haloalkenyl, C3-C8cycloalkyl, phenyl or phenyl substituted by C1-dalkyl, C1-C3haloalkyl, C1-dalkoxy, C1-C3haloalkoxy, halogen, cyano or nitro, heteroaryl or heteroaryl substituted by C1-dalkyl, C1-C3haloalkyl, C1-dalkoxy, C1-dhaloalkoxy, halogen, cyano or nitro, Rc and Rd are each independently of each other hydrogen, C1-d0alkyl, C3-C10alkenyl, C3-Cioalkynyl, C2-d0haloalkyl, C1-docyanoalkyl, C1-Cionitroalkyl, C1-C10aminoalkyl, C1-dalkylaminoC1-dalkyl, C1-ddialkylaminoC1-dalkyl, C3-C7cycloalkylC1-C5alkyl, C1-C5alkoxyC1- C5alkyl, C3-C5alkenyloxyC1-C5alkyl, C1-C5alkynyloxyC1-dalkyl, C1-dalkylthioC1-dalkyl, C1-dalkylsulfinylC1-dalkyl, C1-dalkylsulfonylC1-dalkyl, C2-C8alkylideneaminoxyC1-C5alkyl, C1-C5alkylcarbonylC1-C5alkyl, C1-dalkoxycarbonylC1-dalkyl, aminocarbonylC1-Csalkyl, C1-dalkylaminocarbonylC1-dalkyl, C2-C8dialkylaminocarbonylC1-C5alkyl, C1-C5alkylcarbonylaminoC1-Csalkyl, /V-C1-Csalkylcarbonyl-A/-C1-dalkylaminoalkyl, C1-C8trialkylsilylC1-C5alkyl, phenylCt-C5alkyl (wherein the phenyl may optionally be substituted by C1-C3alkyl, C1-dhaloalkyl, C1-dalkoxy, C1-C3haloalkoxy, C1-dalkylthio, C1-dalkylsulfinyl, C1-dalkylsulfonyl, halogen, cyano, or by nitro), heteroarylC1-C5alkyl, (wherein the heteroaryl may optionally be substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, Cr dalkylthio, C1-dalkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), CrC5haloalkenyl, C3-C8cycloalkyl, phenyl or phenyl substituted by C1-dalkyl, C1-C3haloalkyl, C1-dalkoxy, C1-C3haloalkoxy, halogen, cyano or nitro, heteroaryl or heteroaryl substituted by C1-d alkyl, C1-dhaloalkyl, C1-dalkoxy, CrC3haloalkoxy, halogen, cyano or nitro, heteroarylamino or heteroarylamino substituted by C1-C3 alkyl, C1-dhaloalkyl, C1-dalkoxy, C1-C3haloalkoxy, halogen, cyano or nitro, diheteroarylamino or diheteroarylamino substituted by C1-C3 alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro, phenylamino or phenylamino substituted by C1-dalkyl, C1-dhaloalkyl, C1-dalkoxy, CrC3haloalkoxy, halogen, cyano or by nitro, diphenylamino or diphenylamino substituted by C1-dalkyl, CrC3haloalkyl, C1-C3alkoxy, C1-dhaloalkoxy, halogen, cyano or by nitro, amino, C1-dalkylamino, CrCsdialkylamino, C1-dalkoxy or C3-C7cycloalkylamino, di-C3-C7cycloalkylamino or C3-C7cycloalkoxy or Rc and Rd may join together to form a 3-7 membered ring, optionally containing one heteroatom selected from O or S and optionally substituted by 1 or 2 C1-dalkyl groups. R* is C1-doalkyl, C2-d0alkenyl, C1-doalkynyl, C1-dohaloalkyl, C1-d0cyanoalkyl, C1-C10nitroalkyl, C1-C10aminoalkyl, C1-CsalkylaminoCTCsalkyI, C1-C8dialkylaminoC1-C5alkyl, C3-C7cycloalkylC1-C5alkyl, CrCsalkoxyC^Csalkyl, C3-C5alkenyloxyC1-C5alkyl, C1-CsalkynyloxyC1-C5alkyl, C1-C5alkylthioC1-C5alkyl, C1-C5alkylsulfinylC1-dalkyl, C1-CsalkylsulfonylC1-Csalkyl, Cr C8alkylideneaminoxyC1-C5alkyl, CrC5alkylcarbonylC1-C5alkyl, C1-CsalkoxycarbonylC1-C5alkyl, aminocarbonylC1-C5alkyl, C1-C5alkylaminocarbonylC1-C5alkyl, CrCsdialkylaminocarbonylCr C5alkyl, C1-C5alkylcarbonylaminoC1-C5alkyl, /V-C1-Csalkylcarbonyl-W-C1-dalkylaminoC1-Csalkyl, C3-C6trialkylsilylC1-C5alkyl, phenylC1-C5alkyl (wherein the phenyl may optionally be substituted by C1-dalkyl, C1-C3haloalkyl, C1-C3alkoxy, CrC3haloalkoxy, CTCsalkylthio, CrC3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), heteroarylC1-dalkyl (wherein the heteroaryl may optionally be substituted by C1-dalkyl, C1-dhaloalkyl, C1-dalkoxy, C1-dhaloalkoxy, Cr C3alkylthio, CrCsalkylsulfinyl, C1-dalkylsulfonyl, halogen, cyano, or by nitro), Crdhaloalkenyl, C3-C8cycloalkyl, phenyl or phenyl substituted by C1-dalkyl, C1-dhaloalkyl, C1-dalkoxy, Cr C3haloalkoxy, halogen, cyano or nitro, heteroaryl or heteroaryl substituted by C1-dalkyl, C1- C3haloalkyl, C1-dalkoxy, CrC3haloalkoxy, halogen, cyano, amino or by nitro, heteroarylamino or heteroarylamino substituted by C1-C3alkyl, C1-dhaloalkyl, C1-dalkoxy, C1-dhaloalkoxy, halogen, cyano or by nitro, diheteroarylamino or diheteroarylamino substituted by C1-d alky!, Cr C3haloalkyl, C1-C3alkoxy, C1-dhaloalkoxy, halogen, cyano or nitro, phenylamino or phenylamino substituted by C1-dalkyl, C1-C3haloalkyl, C1-dalkoxy, C1-C3haloalkoxy, halogen, cyano, nitro, amino, diphenylamino, or diphenylamino substituted by C1-dalkyl, C1-dhaloalkyl, CrC3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro, or C3-C7cycloalkylamino, diC3-C7cycloalkylamino or C3-C7cycloalkoxy, C1-doalkoxy, C1-dohaloalkoxy, C1-dalkylamino or drddialkylamino R' and R9 are each independently of each other C1-doalkyl, C2-C10alkenyl, C2-Ci0alkynyl, C1-C10alkoxy, C1-dohaloalkyl, CrCiocyanoalkyl, C1-C10nitroalkyl, CrCioaminoalkyl, C1-dalkylaminoC1-dalkyl, CrddialkylaminoC1-dalkyl, C1-dcycloalkylC1-dalkyl, C1-C5alkoxyC1-C5alkyl, C1-dalkenyloxyC1-Csalkyl, C1-dalkynyloxyC1-dalkyl, C1-C5alkylthioC1-C5alkyl, C1-dalkylsulfinylCrdalkyl, C1-dalkylsulfonylC1-dalkyl, C2-C8alkylideneaminoxyC1-C5alkyl, C1-C5alkylcarbonylC1-C5alkyl, C1-dalkoxycarbonylC1-dalkyl, aminocarbonylC1-dalkyl, C1-CsalkylaminocarbonylC1-Csalkyl, C2-C8dialkylaminocarbonylC1-C5alkyllC1-CsalkylcarbonylaminoC1-C5alkyl, /y/-C1-C5alkylcarbonyl-A/-C2-C5alkylaminoalkyl, C3-C6trialkylsilylC1-C5alkyl, phenylC1-C5alkyl (wherein the phenyl may optionally be substituted by C1-dalkyl, C1-dhaloalkyl, CrC3alkoxy, C^dhaloalkoxy, C1-dalkylthio, CrC3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), heteroarylC1-dalkyl (wherein the heteroaryl may optionally be substituted by C1-dalkyl, CrCahaloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), Crdhaloalkenyl, C3-C8cycloalkyl, phenyl or phenyl substituted by C,-C3alkyl, CrC3haloalkyl, CrC3alkoxy, CA-C3haloalkoxy, halogen, cyano or nitro, heteroaryl or heteroaryl substituted by C1-dalkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or by nitro, heteroarylamino or heteroarylamino substituted by C1-C3 alkyl, CrC3haloalkyl, C1-C3alkoxy, CrCahaloalkoxy, halogen, cyano or by nitro, diheteroarylamino or diheteroarylamino substituted by C1-dalkyl, C1-C3haloalkyl, C1-dalkoxy, C1-C3haloalkoxy, halogen, cyano or nitro, phenylamino or phenylamino substituted by C1-dalkyl, C1-C3haloalkyl, C1-dalkoxy, CrCshaloalkoxy, halogen, cyano or nitro, amino, hydroxyl, diphenylamino, or diphenylamino substituted by C1-dalkyl, C1-dhaloalkyl, C1-dalkoxy, C1-dhaloalkoxy, halogen, cyano or nitro, or C3-C7cycloalkylamino, diC1-C7cycloalkylamino or C3-dcycloalkoxy, C1-Ci0haloalkoxy, C1-dalkylamino or C1-C8dialkylamino, benzyloxy or phenoxy, wherein the benzyl and phenyl groups may in turn be substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro, and Rh is C1-C10alkyl, CrCioalkenyl, C3-C10alkynyl, C1-dohaloalkyl, C1-Ciocyanoalkyl, Cr Cionitroalkyl, CrC10aminoalkyl, C1-dalkylaminoC1-dalkyl, CrC8dialkylaminoC1-Csalkyl, C3-C7cycloalkylC1-C5alkyl, CrCsalkoxyC1-Csalkyl, C1-dalkenyloxyC1-dalkyl, C3-C5alkynyloxyC1- C5alkyl, C1-dalkylthioC1-dalkyl, C1-dalkylsulfinylC1-dalkyl, C1-CsalkylsulfonylC1-C5alkyl, C2-dalkylideneaminoxyC1-dalkyl, C1-dalkylcarbonylC1-Csalkyl, C1-C5alkoxycarbonylC1-C5alkyl, aminocarbonylC1-Csalkyl, CrCsalkylaminocarbonylCrCsalkyl, CrCedialkylaminocarbonylC1-dalkyl, C1-dalkylcarbonylaminoC1-dalkyl, /V-C1-dalkylcarbonyl-W-C1-dalkylaminoC1-dalkyl, C1-dtrialkylsilylC1-dalkyl, phenylC1-C5alkyl (wherein wherein the phenyl may optionally be substituted by C1-dalkyl, C1-C3haloalkyl, C1-dalkoxy, C1-dhaloalkoxy, C1-C3alkylthio, C1-Csalkylsulfinyl, C1-d alkylsulfonyl, halogen, cyano or by nitro), heteroarylC1-dalkyl (wherein the heteroaryl may optionally be substituted by C1-dalkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-dhaloalkoxy, C1-dalkylthio, C1-dalkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), phenoxyC1-dalkyl (wherein wherein the phenyl may optionally be substituted by C1-C3alkyl, C1-dhaloalkyl, C1-C3alkoxy, C1-dhaloalkoxy, C1-dalkylthio, C1-C3alkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), heteroaryloxyC1-C5alkyl (wherein the heteroaryl may optionally be substituted by C1-dalkyl, C1-dhaloalkyl, C1-dalkoxy, C1-dhaloalkoxy, C1-C3alkylthio, Cr C3alkylsulfinyl, C1-d alkylsulfonyl, halogen, cyano or by nitro), C3-C5haloalkenyl, C3-C8cycloalkyl, phenyl or phenyl substituted by C1-dalkyl, C1-dhaloalkyl, CrC3alkoxy, C1-C3haloalkoxy, halogen or by nitro, or heteroaryl, or heteroaryl substituted by C1-dalkyl, C1-dhaloalkyl, C1-dalkoxy, C1-dhaloalkoxy, halogen, cyano or by nitro. In particular, the latentiating group G is a group -C(Xa)-Ra or -C(Xb)-Xc-Rb, and the meanings of Xa, Ra, Xb, Xc and Rb are as defined above. Preferably, G denotes hydrogen, an alkali metal or alkaline earth metal, where hydrogen is particularly preferred. The latentiating groups G are selected to allow its removal by one or a combination of biochemical, chemical or physical processes to afford compounds of formula I where G is H before, during or following application to the treated area or plants. Examples of these processes include enzymatic cleavage, chemical hydrolysis and photolysis. Compounds bearing such groups G may offer certain advantages, such as improved penetration of the cuticula of the plants treated, increased tolerance of crops, improved compatibility or stability in formulated mixtures containing other herbicides, herbicide safeners, plant growth regulators, fungicides or insecticides, or reduced leaching in soils. In a preferred group of compounds of the formula I, R1 is methyl, ethyl, halogen, halomethyl, vinyl, ethynyl or halomethoxy. More preferably, R1 is methyl or ethyl, especially ethyl. It is also preferred that R1 is -OCHF2 or -CF3. Preferably, R2 and R3 are independently hydrogen, optionally substituted phenyl or optionally substituted heteroaryl. More preferably, R2 and R3 are independently hydrogen, phenyl or phenyl substituted by C1-C2alkyl, d^haloalkyl, C1-C2alkoxy, C1-C2haloalkoxy, fluoro, chloro, bromo or cyano, heteroaryl or heteroaryl substituted by C1-C2alkyl, CrC2haloalkyl, C1-dalkoxy, C1-C2haloalkoxy, fluoro, chloro, bromo or cyano. Preferred heteroaryls are thienyl, pyridyl, pyrimidinyl, pyrazolyl and thiazolyl. It is particularly preferred, that R2 is hydrogen and R3 is phenyl or phenyl substituted by C1-C2alkyl, C1-C2haloalkyl, CrC2alkoxy, C1-C2haloalkoxy, fluoro, chloro, bromo or cyano. Preferably, R4 is hydrogen, methyl, ethyl, vinyl or ethynyl and, more preferably, R4 is hydrogen, methyl or ethyl. Preferably, R5 is hydrogen, C1-C4 alkyl, C1-C4alkoxy or C1-C4alkoxyC1-C4alkyl and, more preferably, R5 is hydrogen or methyl, especially hydrogen. Preferably, R6 is hydrogen or methyl and, more preferably, R6 is hydrogen. Preferably, X is optionally substituted C1-C2alkylene. More preferably X is methylene, ethylene, methylene substituted by C1-C3 alkyl, C1-C3alkoxy or C1-C3alkoxyCrC3alkyl or ethylene substituted by C1-C3 alkyl, C1-dalkoxy or C1-dalkoxyC1-C3alkyl. Most preferably, X is methylene or ethylene. Preferably, Y is optionally substituted C1-dalkylene or optionally substituted C2alkenylene. More preferably, Y is C1-C2alkylene or C1-dalkylene substituted by halogen, hydroxyl, cyano, C1-C3alkyl, C1-dalkoxy or C1-C3alkoxyC1-dalkyl, C2alkenylene or C2alkenylene substituted by halogen, hydroxyl, cyano, CrC3alkyl, C1-C3alkoxy or C1-C3alkoxyC1-C3alkyl, in particular ethylene or ethenylene. In a very preferred group of compounds of the formula I, R1 is methyl or ethyl, R2 is hydrogen, R3 is phenyl or phenyl substituted by C1-C2alkyl, C1-C2alkoxy, C1-C2haloalkyl, C1-Cahaloalkoxy, fluoro, chloro, bromo or cyano, R4 is hydrogen, R5 is hydrogen, R6 is hydrogen, X is methylene, Y is ethylene and G is hydrogen. The invention relates also to the salts which the compounds of formula I are able to form with amines, alkali metal and alkaline earth metal bases or quaternary ammonium bases. Among the alkali metal and alkaline earth metal hydroxides as salt formers, special mention should be made of the hydroxides of lithium, sodium, potassium, magnesium and calcium, but especially the hydroxides of sodium and potassium. The compounds of formula I according to the invention also include hydrates which may be formed during the salt formation. Examples of amines suitable for ammonium salt formation include ammonia as well as primary, secondary and tertiary C1-Ci8alkylamines, C1-C^ydroxyalkylamines and C2-C4-alkoxyalkylamines, for example methylamine, ethylamine, n-propylamine, isopropylamine, the four butylamine isomers, n-amylamine, isoamylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, pentadecylamine, hexadecylamine, heptadecylamine, octadecylamine, methylethylamine, methylisopropylamine, methylhexylamine, methylnonylamine, methylpentadecylamine, methyloctadecylamine, ethylbutylamine, ethylheptylamine, ethyloctylamine, hexylheptylamine, hexyloctylamine, dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, di-n-butylamine, di-n-amylamine, diisoamylamine, dihexylamine, diheptylamine, dioctylamine, ethanolamine, n-propanolamine, isopropanolamine, N,N-diethanolamine, N-ethylpropanolamine, N-butylethanolamine, allylamine, n-but-2-enylamine, n-pent-2-enylamine, 2,3-dimethylbut-2-enylamine, dibut-2-enylamine, n-hex-2-enylamine, propylenediamine, trimethylamine, triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, triisobutylamine, tri-sec-butylamine, tri-n-amylamine, methoxyethylamine and ethoxyethylamine; heterocyclic amines, for example pyridine, quinoline, isoquinoline, morpholine, piperidine, pyrrolidine, indoline, quinuclidine and azepine; primary arylamines, for example anilines, methoxyanilines, ethoxyanilines, o-, m- and p-toluidines, phenylenediamines, benzidines, naphthylamines and o-, m- and p-chloroanilines; but especially triethylamine, isopropylamine and diisopropylamine. Preferred quaternary ammonium bases suitable for salt formation correspond, for example, to the formula [N(Ra RbRc R Y is CH=CH, R1 and R4 are ethyl, R5 and R6 are hydrogen, G is hydrogen and R2 and R3 are as defined in Table 1. Table 16: This table covers 202 compounds of formula I, wherein X is CH2, Y is CH2-CH2, R1 is methyl, R4, R5 and R6 are hydrogen, G is hydrogen and R2 and R3 are as defined in Table 1. Table 17: This table covers 202 compounds of formula I, wherein X is CH2, Y is CH2-CH2> R1 is ethyl, R4, R5 and R6 are hydrogen, G is hydrogen and R2 and R3 are as defined in Table 1. Table 18: This table covers 202 compounds of formula I, wherein X is CH2, Y is CH2-CH2, R1 and R4 are methyl, R5 and R6 are hydrogen, G is hydrogen and R2 and R3 are as defined in Table 1. Table 19: This table covers 202 compounds of formula I, wherein X is CH2, Y is CH2-CH2, R1 is ethyl, R4 is methyl, Rs and R6 are hydrogen, G is hydrogen and R2 and R3 are as defined in Table 1. Table 20: This table covers 202 compounds of formula I, wherein X is CH2-CH2, Y is CH2-CH2, R1 and R4 are methyl, R5 and R6 are hydrogen, G is hydrogen and R2 and R3 are as defined in Table 1. Table 29: (TABLE REMOVED) Pivaloyl chloride (248 \i\, 2 mmol) is added to a solution of 3-(3,5-dimethylbiphen-4-yl)bicyclo[3.2.1]octane-2,4-dione (148 mg, 0.46 mmol) in dichloromethane (10 ml) and triethylamine (280 jil, 2 mmol) at room temperature. The reaction mixture is stirred at room temperature overnight. The reaction mixture is evaporated under reduced pressure and the residue is purified by column chromatography on silica gel to afford 3-(3,5-dimethylbiphen-4-yl)-4-oxo-bicyclo[3.2.1Joct-2-en-2-yl2,2-dimethylpropionate. Example 24: Preparation of carbonic acid 3-(2'.4'-dichloro-4-ethylbiphen-3-vn-4-oxo-bicvclof3.2.noct-2-en-2-yl ester methyl ester (FORMULA REMOVED) To a solution of 3-(2\4'-dichloro-4-ethylbiphen-3-yl)-bicydo[3.2.1]octane-2,4-dione (0.133g, 0.34 mmol) in dichloromethane (2 ml) is added triethylamine (0.24 ml, 1.72 mmol) followed by stirring at room temperature for 5 minutes. To this solution is added methyl chloroformate (0.132 ml, 172mmol) dropwise, then the mixture is left to stand overnight. The reaction mixture is concentrated in vacuo to afford a crude soild which is purified by flash column chromatography on silica gel (100% to 70% hexane/ethyl acetate eluant ratio) to afford carbonic acid 3-(2',4'-dichloro-4-ethylbiphen-3-yl)-4-oxo-bicyclo[3.2.1]oct-2-en-2-yl ester methyl ester. Additional compounds in Table T2 below were prepared by similar methods using appropriate starting materials. (TABLE REMOVED) Seeds of a variety of test species were sown in standard soil in pots. After cultivation for one day (TABLE REMOVED) We Claim: 1. A compound of formula I (Formula Removed) wherein R1 is methyl, ethyl, n-propyl, /so-propyl, cyclopropyl, halomethyl, haloethyl, halogen, vinyl, ethynyl, methoxy, ethoxy, halomethoxy or haloethoxy; R2and R3 are independently hydrogen, halogen, C1-C6alkyl, C1-C6haloalkyl, C1-C6alkoxy, C1-C6haloalkoxy, C2-C6alkenyl, C2-C6haloalkenyl, C2-C6alkynyl, C3-C6alkenyloxy, C3. C6haloalkenyloxy, C3-C6alkynyloxy, C3-C6cycloalkyl, C1-C6alkylthio, C1-C6alkylsulfinyl, C1-C6alkylsulfonyl, C1-C6alkylsulfonyloxy, C1-C6haloalkylsulfonyloxy, cyano, nitro, optionally substituted phenyl or optionally substituted heteroaryl; wherein at least one of R2 and R3 is optionally substituted phenyl or optionally substituted heteroaryl, in which the heteroaryl and the phenyl are optionally substituted by one or more substituents selected from C1-C4alkyl, C2-C4alkenyl, C2-C4alkynyl, C1-C4haloalkyl, C3-C7cycloalkyl, C5-C7cycloalkenyl, C1-C4alkoxy, C1-C4haloalkoxy, C1-C4alkylthio, C1-C4haloalkylthio, C1-C4alkylsulfinyl, C1-C4haloalkylsulfinyl, C1-C4alkylsulfonyl, C1-C4haloalkylsulfonyl, fluoro, chloro, bromo, iodo, cyano, nitro, hydroxy-C1-C4alkyl, formyl, carboxy, C1-C4alkylcarbonyl, C1-C4alkoxycarbonyl, amidocarbonyl, C1-C4alkylaminocarbonyl, di-C1-C4alkylaminocarbonyl, amino, C1-C4alkylcarbonylamino, C1-C4alkoxycarbonylamino, C1-C4alkylaminocarbonylamino, diC1-C4alkylaminocarbonylamino, C1-C4alkylsulfonylamino, C1-C4haloalkylsulfonylamino, C1-C4alkylsulfonyloxy and C1-C4haloalkylsufonyloxy; R4 is hydrogen, methyl, ethyl, n-propyl, /so-propyl, halomethyl, haloethyl, halogen, vinyl, ethynyl, methoxy, ethoxy, halomethoxy or haloethoxy; R5 and R6 are independently hydrogen, C1-C6alkyl, C2-C6alkenyl, C2-C6alkynyl, C1-C6haloalkyl, C2-C6haloalkenyl, C1-C6alkoxy, C3-C6alkenyloxy, C3-C6halqalkenyloxy, C3-C6alkynyloxy, C1-C4alkoxyC1-C4alkyl, C1-C4alkoxyC1-C4akoxy, C1-C4alkoxyC1-C4alkoxyC1-C4alkyl, C1-C6alkylthio, C1-C4alkylthioC1-C4alkyl, C1-C4alkylsulfinyl, C1-C4alkylsulfinylC1-C4alkyl, C1-C4alkylsulfonyl, C1- C4alkylsulfonylC1-C4alkyl, hydroxy-C1-C4alkyl, C1-C6haloalkoxyC1-C4alkyl, C3-C6alkenyloxyd-C4alkyl, C3-C6haloalkenyloxyC1-C4alkyl, C3-C6alkynyloxyC1-C4alkyl, C1-C6cyanoalkyl, C1-C6cyanoalkoxy, C1-C4cyanoalkoxyC1-C4alkyl, hydroxy, C1-C6alkylcarbonyl, carboxy, C1-C6alkoxycarbonyl, C1-C6alkylaminocarbonyl, di-C1-C6alkylcarbonyl, tri(C1-C4alkyl)silyl or tri(C1-C4alkyl)silyloxy; X is optionally substituted C1-C3alkylene; and Y is optionally substituted C1-C3alkylene or optionally substituted C2-C3alkenylene; wherein the C1-C3alkylene and C2-C3alkenylene groups X and Y are unsubstituted, or are substituted once or twice by C1-C4alkyl, C1-C4alkoxy, C1-C4alkoxyd-dalkyl, halogen or hydroxy; and G is hydrogen, an alkali metal, alkaline earth metal, sulfonium, ammonium, C1-C6 alkyl, C3-C6 alkenyl, C3-C6alkynyl, or a latentiating group; and wherein, when G is a latentiating group, then G is C1-C8 alkyl, C2-C8 haloalkyl, phenylC1-C8alkyl (wherein the phenyl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), heteroaryld-C8alkyl (wherein the heteroaryl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), C3-C8 alkenyl, C3-C8 haloalkenyl, C3-C8 alkynyl, C(Xa)-Ra, C(Xb)-Xc-Rb, C(Xd)-N(Rc)-Rd, -SO2-Re, -P(Xe)(Rf)-R9 or CH2-Xf-Rh; wherein Xa, Xb, Xc, Xd, X8 and X' are independently of each other oxygen or sulfur; and wherein Ra is H, C1-C18 alkyl, C2-C18alkenyl, C2-C18alkynyl, C1-C10haloalkyl, C1-C10cyanoalkyl, C1-C10nitroalkyl, C1-C10aminoalkyl, C1-C5alkylaminoC1-C5alkyl, C2-C8dialkylaminoC1-C5alkyl, C3-C7cycloalkylC1-C5alkyl, C1-C5alkoxyC1-C5alkyl, C3-C5alkenyloxyC1-C5alkyl, C3-C5alkynyloxyC1-C5alkyl, C1-C5alkylthioC1-C5alkyl, C1-C5alkylsulfinylC1-C5alkyl, C1-C5alkylsulfonylC1-C5alkyl, C2-C8alkylideneaminoxyC1-C5alkyl, C1-C5alkylcarbonylC1-C5alkyl, C1-C5alkoxycarbonylC1-C5alkyl, aminocarbonylC1-C5alkyl, C1-C5alkylaminocarbonylC1-C5alkyI, C2-C8dialkylaminocarbonylC1-C5alkyl, C1-C5alkylcarbonylaminoC1-C5alkyl, N-C1-C5alkylcarbonyl-N-C1-C5alkylaminod-dalkyl, C3-C6trialkylsilylC1-C5alkyl, phenylC1-C5alkyl (wherein the phenyl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), heteroarylC1-C5alkyl (wherein the heteroaryl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), C2-C5haloalkenyl, C3-C8cycloalkyl; phenyl or phenyl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; or heteroaryl or heteroaryl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; Rb is C1-C18alkyl, C3-C18alkenyl, C3-C18alkynyl, C2-C10haloalkyl, C1-C10cyanoalkyl, C1-C10nitroalkyl, C2-C10aminoalkyl, C1-C5alkylaminoC1-C5alkyl, C2-C8dialkylaminoC1-C5alkyl, C3-C7cycloalkylC1-C5alkyl, C1-C5alkoxyC1-C5alkyl, C3-C5alkenyloxyC1-C5alkyl, C3-C5alkynyloxyC1-Csalkyl, C1-C5alkylthioC1-C5alkyl, C1-C5alkylsulfinylC1-C5alkyl, C1-C5alkylsulfonylC1-C5alkyl, C2-C8alkylideneaminoxyC1-C5alkyl, C1-C5alkylcarbonylC1-C5alkyl, C1-C5alkoxycarbonylC1-C5alkyl, aminocarbonylC1-C5alkyl, C1-C5alkylaminocarbonylC1-C5alkyl, C2-C8dialkylaminocarbonylC1-C5alkyl, d-dalkylcarbonylaminod-dalkyl, N-C1-C5alkylcarbonyl-N-C1-C5alkylaminoC1-C5alkyl, C3-C6trialkylsilylC1-C5alkyl, phenylC1-C5alkyl (wherein the phenyl is optionally substituted by C1-C3alkyl, Crdhaloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), heteroaryld-dalkyl (wherein the heteroaryl is optionally substituted by d-dalkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), C3-C5haloalkenyl, C3-C8cycloalkyl; phenyl or phenyl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; or heteroaryl or heteroaryl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; and Rc and Rd are each independently of each other hydrogen, C1-C10alkyl, C3-C10alkenyl, C3-C10alkynyl, C2-C10haloalkyl, C1-C10cyanoalkyl, C1-C10nitroalkyl, C1-C10aminoalkyl, C1-C5alkylaminoC1-C5alkyl, C2-C8dialkylaminoC1-C5alkyl, C3-C7cycloalkylC1-C5alkyl, C1-C5alkoxyC1-C5alkyl, C3-C5alkenyloxyC1-C5alkyl, C3-C5alkynyloxyC1-C5alkyl, C1-C5alkylthioC1-C5alkyl, C1-C5alkylsulfinylC1-C5alkyl, C1-C5alkylsulfonylC1-C5alkyI, C2-C8alkylideneaminoxyC1-C5alkyl, C1-C5alkylcarbonylC1-C5alkyl, C1-C5alkoxycarbonylC1-C5alkyl, aminocarbonylC1-C5alkyl, C1-C5alkylaminocarbonylC1-C5alkyl, C2-C8dialkylaminocarbonylC1-C5alkyl, C1-C5alkylcarbonylaminoC1-C5alkyl, N-C1-C5alkylcarbonyl-N-C2-C5alkylaminoalkyl, C3-C6trialkylsilylC1-C5alkyl, phenylC1-C5alkyl (wherein the phenyl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), heteroarylC1-C5alkyl (wherein the heteroaryl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), C2-C5haloalkenyl, C3-C8cycloalkyl; phenyl or phenyl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; heteroaryl or heteroaryl substituted by C1-C3 alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; heteroarylamino or heteroarylamino substituted by C1-C3 alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; diheteroarylamino or diheteroarylamino substituted by C1-C3 alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; phenylamino or phenylamino substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or by nitro; diphenylamino or diphenylamino substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-dhaloalkoxy, halogen, cyano or by nitro; or amino, C1-C3alkylamino, C1-C3dialkylamino, C1-C3alkoxy, C3-C7cycloalkylamino, di-C3-C7cycloalkylamino or C3-C7cycloalkoxy; or Rc and Rd are joined together to form a 3-7 membered ring, optionally containing one heteroatom selected from O or S and optionally substituted by 1 or 2 C1-C3alkyl groups; and Re is C1-C10alkyl, C2-C10alkenyl, C2-C10alkynyl, C1-C10ohaloalkyl, C1-C10cyanoalkyl, C1-C10nitroalkyl, C1-C10aminoalkyl, C1-C5alkylaminoCi-Csalkyl, C2-C8dialkylaminoC1-C5alkyl, C3-C7cycloalkylC1-C5alkyl, C1-C5alkoxyC1-C5alkyl, C3-C5alkenyloxyd-C5alkyl, C3-C5alkynyloxyC1-C5alkyl, C1-C5alkylthioC1-C5alkyl, C1-C5alkylsulfinylC1-C5alkyl, C1-C5alkylsulfonylC1-C5alkyl, C2-C6alkylideneaminoxyC1-C5alkyl, C1-C5alkylcarbonylC1-C5alkyl, C1-C5alkoxycarbonylC1-C5alkyl, aminocarbonylC1-C5alkyl, C1-C5alkylaminocarbonylC1-C5alkyl, C2-C8dialkylaminocarbonylC1-C5alkyl, C1-C5alkylcarbonylaminoC1-C5alkyl,N-C1-C5alkylcarbonyl-N-C1-C5alkylaminoC1-C5alkyl, C3-C6trialkylsilylC1-C5alkyl, phenylC1-C5alkyl (wherein the phenyl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), heteroarylC1-C5alkyl (wherein the heteroaryl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), C2-C5haloalkenyl, C3-C8cycloalkyl; phenyl or phenyl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; heteroaryl or heteroaryl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano, amino or by nitro; heteroarylamino or heteroarylamino substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or by nitro; diheteroarylamino or diheteroarylamino substituted by C1-C3 alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; phenylamino or phenylamino substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano, or nitro; amino; diphenylamino or diphenylamino substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; or C3-C7cycloalkylamino, diC3-C7cycloalkylamino, C3-C7cycloalkoxy, C1-C10alkoxy, C1-C10haloalkoxy, C1-C5alkylamino or C2-C8dialkylamino; Rf and Rg are each independently of each other C1-C10alkyl, C2-10alkenyl, C2-C10alkynyl, C1-C10alkoxy, C1-C10haloalkyl, C1-C10cyanoalkyl, C1-C10 nitroalkyl, C1-C10aminoalkyl, C1-C5alkylaminoC1-C5alkyl, C2-C8dialkylaminoC1-C5alkyl, C3-C7cycloalkylC1-C5alkyl, C1-C5alkoxyC1-C5alkyl, C3-C5alkenyloxyd-C5alkyl, C3-C5alkynyloxyd-C5alkyl, C1-C5alkylthioC1-C5alkyl, C1-C5alkylsulfinylC1-C5alkyl, C1-C5alkylsulfonylC1-C5alkyI, C2-C8alkylideneaminoxyC1-C5alkyl, C1-C5alkylcarbonylC1-C5alkyl, C1-C5alkoxycarbonylC1-C5alkyl, aminocarbonylC1-C5alkyl, C1-C5alkylaminocarbonylC1-C5alkyl, C2-C8dialkylaminocarbonylC1-C5alkyl, C1-C5alkylcarbonylaminoC1-C5alkyl, N-C1-C5alkylcarbonyl-N-C2-C5alkylaminoalkyl, C3-C6trialkylsilylC1-C5alkyl, phenylC1-C5alkyl (wherein the phenyl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C5alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), heteroarylC1-C5alkyl (wherein the heteroaryl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3alkylsulfonyl, halogen, cyano, or by nitro), C2-C5haloalkenyl, C3-C8cycloalkyl; phenyl or phenyl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1- C3haloalkoxy, halogen, cyano or nitro; heteroaryl or heteroaryl substituted by C1-C3alkyl, C-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or by nitro; heteroarylamino or heteroarylamino substituted by C1-C3 alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or by nitro; diheteroarylamino or diheteroarylamino substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; phenylamino or phenylamino substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; amino; hydroxyl; diphenylamino or diphenylamino substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; or C3-C7cycloalkylamino, diC3-C7cycloalkylamino, C3-C7cycloalkoxy, C1-C10haloalkoxy, C1-C5alkylamino or C2-C8dialkylamino; or benzyloxy or phenoxy, wherein the benzyl and phenyl groups may in turn be substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or nitro; and Rh is C1-C10alkyl, C3-C10alkenyl, C3-C10alkynyl, C1-C10haloalkyl, C1-C10cyanoalkyl, C1-C10nitroalkyl, C2-C10aminoalkyl, C1-C5alkylaminoC1-C5alkyl, C2-C8dialkylaminoC1-C5alkyl, C3-C7-cycloalkylC1-C5alkyl, C1-C5alkoxyC1-C5alkyl, C3-C5alkenyloxyC1-C5alkyl, C3-C5alkynyloxyC1-C5alkyl, C1-C5alkylthioC1-C5alkyl, C1-C5alkylsulfinylC1-C5alkyl, C1-C5alkylsulfonylC1-C5alkyl, C2-C8alkylideneaminoxyC1-C5alkyl, C1-C5alkylcarbonylC1-C5alkyl, C1-C5alkoxycarbonylC1-C5alkyl, aminocarbonylC1-C5alkyl, C1-C5alkylaminocarbonylC1-C5alkyl, C2-C8dialkylaminocarbonylC1-C5alkyl, C1-C5alkylcarbonylaminoC1-C5alkyl, N-C1-C5alkylcarbonyl-N-C1-C5alkylaminoC1-C5alkyl, C3-C6trialkylsilylC1-C5alkyl, phenylC1-C5alkyl (wherein the phenyl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), heteroarylC1-C5alkyl (wherein the heteroaryl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), phenoxyC1-C5alkyl (wherein the phenyl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), heteroaryloxyC1-C5alkyl (wherein the heteroaryl is optionally substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, d-dhaloalkoxy, C1-C3alkylthio, C1-C3alkylsulfinyl, C1-C3 alkylsulfonyl, halogen, cyano or by nitro), C3-C5haloalkenyl, C3-C8cycloalkyl; phenyl or phenyl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen or by nitro; or heteroaryl or heteroaryl substituted by C1-C3alkyl, C1-C3haloalkyl, C1-C3alkoxy, C1-C3haloalkoxy, halogen, cyano or by nitro; and wherein "heteroaryl" means thienyl, furyl, pyrrolyl, isoxazolyl, oxazolyl, isothiazolyl, thiazolyl, pyrazolyl, imidazolyl, triazolyl, tetrazolyl, pyridyl, pyrimidinyl, pyrazinyl, pyridazinyl, triazinyl, oxadiazolyl or thiadiazolyl, or, where appropriate, an N-oxide or a salt thereof. 2. A compound according to claim 1, wherein R1 is methyl, ethyl, halogen, halomethyl, vinyl, ethynyl or halomethoxy. 3. A compound according to claim 2, wherein R1 is methyl or ethyl. 4. A compound according to claim 3, wherein R1 is ethyl. 5. A compound according to claim 2, wherein R1 is -OCHF2 or-OCF3. 6. A compound according to claim 1, 2, 3 or 4, wherein R2 and R3 are independently hydrogen, optionally substituted phenyl or optionally substituted heteroaryl. 7. A compound according to claim 6, wherein R2 and R3 are independently hydrogen; phenyl or phenyl substituted by C1-C2alkyl, C1-C2alkoxy, C1-C2haloalkyl, C1-C2haloalkoxy, fluoro, chloro, bromo or cyano; or heteroaryl or heteroaryl substituted by C1-C2alkyl, C1-C2alkoxy, C1-C2haloalkyl, C1-C2haloalkoxy, fluoro, chloro, bromo or cyano. 8. A compound according to claim 7, wherein R2 is hydrogen and R3 is phenyl or phenyl substituted by C1-C2alkyl, C1-C2alkoxy, C1-C2haloalkyl, C1-C2haloalkoxy, fluoro, chloro, bromo or cyano. 9. A compound according to any of claims 1 to 4 or 6 to 8, wherein R4 is hydrogen, methyl, ethyl, vinyl or ethynyl. 10. A compound according to claim 9, wherein R4 is hydrogen, methyl or ethyl. 11. A compound according to any of claims 1 to 4 or 6 to 10, wherein R5 is hydrogen, C1-C4 alkyl, C1-C4alkoxy or C1-C4alkoxyC1-C4alkyl. 12. A compound according to claim 11, wherein R5 is hydrogen or methyl. 13. A compound according to any of claims 1 to 4 and 6 to 12, wherein R6 is hydrogen or methyl. 14. A compound according to claim 13, wherein R6 is hydrogen. 15. A compound according to any of claims 1 to 4 or 6 to 14, wherein X is optionally substituted C1-C2alkylene. 16. A compound according to claim 15, wherein X is methylene, ethylene, methylene substituted by C1-C3 alkyl, C1-C3alkoxy or C1-C3alkoxyC1-C3alkyl or ethylene substituted by C1-C3 alkyl, C1-C3alkoxy or C1-C3alkoxyC1-C3alkyl. 17. A compound according to claim 16, wherein X is methylene or ethylene. 18. A compound according to any of claims 1 to 4 or 6 to 17, wherein Y is optionally substituted C1-C2alkylene or optionally substituted C2alkenylene. 19. A compound according to claim 18, wherein Y is C1-C2alkylene or C1-C2alkylene substituted by halogen, hydroxyl, C1-C3alkyl, C1-C3alkoxy or C1-C3alkoxyC1-C3alkyl; or C2alkenylene or C2alkenylene substituted by halogen, hydroxyl, C1-C3alkyl, C1-C3alkoxy or C1-C3alkoxyC1-C3alkyl. 20. A compound according to claim 19, wherein Y is ethylene or ethenylene. 21. A compound according to claim 1, wherein R1 is methyl or ethyl, R2 is hydrogen, R3 is phenyl or phenyl substituted by C1-C2alkyl, C1-C2alkoxy, C1-C2haloalkyl, C1-C2haloalkoxy, fluoro, chloro, bromo or cyano, R4 is hydrogen, R5 is hydrogen, R6 is hydrogen, X is methylene, Y is ethylene and G is hydrogen. 22. A compound according to any of claims 1 to 4 or 6 to 20, wherein, when G is a latentiating group, then G is a group -C(Xa)-Ra or -C(Xb)-Xc-Rb, and the meanings of Xa, Ra, Xb, Xc and Rb are as defined in claim 1. 23. A compound according to any of claims 1 to 4 or 6 to 20, wherein, G is hydrogen. 24. A process for the preparation of a compound of formula I according to claim 1, wherein G is hydrogen, which comprises reacting a compound of the formula (J) (Formula Removed) wherein X, Y, R5 and R6 are as defined in claim 1, with a compound of formula (M) (Formula Removed) wherein R1, R2, R3and R4 are as defined in claim 1 and Hal represents chlorine, bromine or iodine in the presence of a catalyst, a ligand, a base and a solvent. 25. A process for the preparation of a compound of formula I according to claim 1 which comprises reacting a compound of the formula (T) (Formula Removed) wherein Hal represents chlorine, bromine or iodine and X, Y, R1, R3, R4, R5, R6and G are as defined in claim 1, with a compound of the formula R2-B(OH)2, or an ester or salt thereof, wherein R2 is optionally substituted phenyl or optionally substituted heteroaryl, in the presence of a catalyst, a ligand, a base and a solvent. 26. A process for the preparation of a compound of formula I according to claim 1 which comprises reacting a compound of the formula (T1) (Formula Removed) wherein Hal represents chlorine, bromine or iodine and X, Y, R1, R2, R4,R5, R6and G are as defined in claim 1, with a compound of the formula R3-B(OH)2, or an ester or salt thereof, wherein R3 is optionally substituted phenyl or optionally substituted heteroaryl, in the presence of a catalyst, a ligand, a base and a solvent. 27. A process for the preparation of a compound of formula I according to claim 1 which comprises reacting a compound of the formula (Y) (Formula Removed) wherein R1, R3, R4,R5, R6,and X, Y and G are as defined in claim 1, or an ester or salt thereof, with a compound of the formula R2-Hal, wherein R2 is optionally substituted phenyl or optionally substituted heteroaryl and Hal is chlorine, bromine or iodine, in the presence of a catalyst, a ligand, a base and a solvent. 28. A process for the preparation of a compound of formula I according to claim 1 which comprises reacting a compound of the formula (Yi) (Formula Removed) wherein R1, R2, R4,R5, R6and X, Y and G are as defined in claim 1, or an ester or salt thereof, with an aryl- or heteroaryl halide of formula R3-Hal, wherein R3is as defined in claim 1 and Hal is chlorine, bromine or iodine, in the presence of a catalyst, a ligand, a base and a solvent. 29. A method of controlling grasses and weeds in crops of useful plants, which comprises applying a herbicidally effective amount of a compound of formula I as defined in any one of claims 1 to 23, or of a composition comprising such a compound, to the plants or to the locus thereof. 30. A method according to claim 29, which comprises applying a herbicidally effective amount of a composition comprising the compound of formula I to the plants or to the locus thereof, and wherein the crops of useful plants are cereals, cotton, soybeans, sugar beet, sugar cane, plantation crops, rape, maize or rice. 31. A herbicidal composition, which, in addition to comprising formulation adjuvants, comprises a herbicidally effective amount of a compound of formula I as defined in any one of claims 1 to 23. 32. A composition according to claim 31, which, in addition to comprising the compound of formula I, comprises a further herbicide as mixing partner. 33. A composition according to claim 31, which, in addition to comprising the compound of formula I, comprises a safener. 34. A composition according to claim 31, which, in addition to comprising the compound of formula I, comprises a further herbicide as mixing partner and a safener.