Pyrone compounds and herbicides comprising the same

A pyrone compound of formula (I):

• wherein:
• m is 2;
• n is an integer of any one of 1 to 3;
• X is O, S, S(O) or S(O)2;
• R1 is a hydrogen atom or a methyl group;
• R2 and R3 are each independently of each other a hydrogen atom, a methyl group, or an ethyl group, or alternatively R2 and R3 connect with each other to form an ethylene chain with the proviso that two R2 may be the same or different to each other and two R3 may be the same or different to each other;
• R4 is a phenyl group, a 2-pyridyl group, a 3-furyl group, a 2-thienyl group, a 2-thiazolyl group or a 2-(1,3,4-triazolyl) group, wherein the phenyl group, the 2-pyridyl group, the 3-furyl group, the 2-thienyl group, the 2-thiazolyl group and the 2-(1,3,4-triazolyl) group each have at least one substituent selected from the group consisting of a chlorine atom, a bromine atom, an iodine atom, a fluorine atom, a methyl group, an ethyl group, an isopropyl group, a tert-butyl group, a methoxy group, a nitro group, an amino group, a cyano group, a hydroxyl group, an acetyl group, a methoxycarbonyl group, a pentafluorothio group, a pentafluoroethyl group, a difluoroethyl group, a heptafluoroisopropyl group, a trifluoromethylthio group, a trifluoromethoxy group and a trifluoromethyl group;
• G is a hydrogen atom, an acetyl group, a propionyl group, a butylcarbonyl group, a benzoyl group, a methylsulfonyl group, a methoxycarbonyl group, an ethoxycarbonyl group, an allyloxycarbonyl group, a phenoxycarbonyl group, a methoxymethyl group or an ethoxymethyl group;
• and
• Z is a methyl group, an ethyl group, a phenyl group, a vinyl group, a cyclopropyl group, a nitro group, a fluorine atom, a chlorine atom, a bromine atom, a methoxy group, a trifluoromethyl group, a 5-trifluoromethyl-2-chloropyridyloxy group or an ethynyl group,
• or an agronomically acceptable salt thereof.