Abstract: A method of killing or controlling unwanted plants by applying to the plant on to a locus thereof an effective amount of a compound of formula (I) ##STR1## or a salt thereof: wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are independently selected from hydrogen, hydroxy, alkyl, alkoxy, alkylcarbonyl, halogen, cyans, nitro, haloalkyl and haloalkoxy; R.sup.6 is hydrogen, hydroxy, amino, lower alkyl, halogen, cyano, haloalkyl, nitro, aryl, or a group C(O).sub.m R.sup.10, wherein R.sup.10 is hydrogen, alkyl, alkenyl, alkynyl or phenyl any of which may be optionally substituted and m is 1 or 2; R.sup.7 is hydrogen, lower alkyl, haloalkyl, C(O).sub.m R.sup.10 or halogen; or R.sup.6 and R.sup.7 together form an optionally substituted alkylene chain of 2 or 3 carbon atoms; R.sup.8 is hydrogen, lower alkyl or halogen or the group R.sup.7 or R.sup.8 together form an oxo group; and the group CZR.sup.9 is carboxy or an ester thereof, or R.sup.9 is a group SR.sup.10 or NR.sup.11 R.sup.12 wherein R.sup.