A method for controlling aquatic weeds which comprises applying a herbicidally effective amount of a solid formulation of at least one compound of formula (I) wherein X is halogen and R is halogen or C1-C6 alkyl, and/or one or more agriculturally acceptable salts thereof to the bottom of the aqueous habitat of the aquatic weeds to act on submersed aquatic weeds and/or their aqueous habitat containing seeds or other propagating organs of said aquatic weeds.