A method of combating root weevils comprising contacting the root weevils or their food supply, habitat, breeding grounds or their locus with a pesticidally effective amount of a compound of the formula (I) wherein W is Cl or CF3; X and Y are each independently Cl or Br; R1 is alkyl, alkenyl, alkynyl, or cycloalkyl optionally substituted with 1 to 3 halogens, or alkyl which is substituted by alkoxy; R2 and R3 are alkyl or may be taken together to form cycloalkyl optionally substituted by 1 to 3 halogens; R4 is H or C1-C6-alkyl, or the enantiomers or salts thereof.