A SYNERGISTIC COMPOSITION AND A PROCESS FOR SELECTIVELY COMBATING WEEDS, ESPECIALLY IN CEREAL CROPS

1. A synergistic composition for selectively controlling weeds, which composition contains as active ingredients, on the one hand, 3-(4-isopropylphenyl)-1,1-dimethylurea (Ia) or 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea (Ib), and, on the other hand, a halopyridyloxyphenoxyalkanecarboxylic acid derivative of the formula II see diagramm : EP0069705,P17,F1 wherein Hal is halogen, R is hydrogen, halogen or C1 -C4 alkyl, alkylene is a saturated, straight chain or branched C2 -C4 alkylene chain, X is any one of the groups -O(cation) Y(anion), -O-R1 , -S-R2 , -NR3 R4 or -O-N=CR6 R7 , where R1 and R2 are each hydrogen, C1 -C5 alkyl, C1 -C4 haloalkyl, C2 -C6 haloalkenyl, C2 -C6 alkenyl, C3 -C6 alkynyl, C3 -C6 haloalkynyl, C2 -C4 carboxyalkyl, C1 -C4 cyanoalkyl, C1 -C4 hydroxyalkyl, C1 -C4 aminocarboxyalkyl, C3 -C6 alkoxycarboxyalkyl unsubstituted or substituted by cyano, -COO-alkyl or -CO-alkyl, or R1 and R2 are each phenyl or phenylalkyl having 1 to 3 carbon atoms in the alkyl moiety, the phenyl or phenylalkyl each being unsubstituted or substituted by nitro, cyano, halogen or C1 -C4 alkyl, or R1 and R2 are one of the groups C2 -C4 alkylene-NR3 R4 or C2 -C4 alkylene-N(anion) R3 R4 R5 Z(cation), R3 is hydrogen, C1 -C4 alkyl, C3 -C5 alkoxyalkyl, C1 -C4 haloalkyl, C2 -C4 carboxyalkyl, C3 -C6 alkoxycarboxyalkyl, C1 -C4 hydroxyalkyl or -CO-alkyl, R4 is hydrogen, C1 -C4 alkyl, C2 -C4 alkenyl or C1 -C4 hydroxyalkyl, R5 is hydrogen or C1 -C4 alkyl, R6 and R7 are each C1 -C4 alkyl, Y(anion) is a cation of an alkali metal or alkaline earth metal or of ammonium, Z(cation) is a halogen anion, or wherein R3 and R4 together with the nitrogen atom to which they are attached can form a pyrrolidine, piperidine, morpholine, thiomorpholine, piperazine, pyrazole or triazole ring, and R6 and R7 together with the nitrogen atom to which they are attached can form a pyrrolidine or piperidine ring, with the exception of the two compounds : propargyl 4-(3'-5'-dichloropyridyl-2'-oxy)- alpha-phenoxypropionate and propargyl 4-(3'-5'-dichloropyridyl-2'-oxy)- alpha-phenoxythiopropionate, together with carriers and/or other adjuvants.