1. A herbicidal composition which, in addition to comprising customary inert formulation adjuvants, comprises: a) a herbicidally effective amount of at least one compound of formula (I) wherein R is C1-C2alkyl or chlorine, R1 is hydrogen or C1-C4alkyl and R2 is C1-C4alkyl, or an agronomically acceptable salt of such a compound, especially the sodium or ammonium salt, and b) an amount effective for herbicide synergism of an active ingredient known for its insecticidal action.