Abstract: There is provided apparatus for use in applying a treating liquid chemical to surfaces at or adjacent a longitudinal channel and including a first chemical applicator assembly (11) and a second assembly (10) mounted on a frame (31) adapted to be connected to and extend from one side of a tractor (9) or other conveyance whereby the applicator assemblies (11, 10) may be drawn along said surfaces and raised or lowered in use, each applicator assembly having an applicator head (14, 13) for supplying said liquid chemical and being mounted on a support housing (17, 16) having wheel means (21) therebeneath, the support housing (16) of the second applicator assembly (11) being further from the tractor (9) than the other and the two being hingedly interconnected and tiltable relative to the frame (31) and to each other about parallel longitudinal axes for treating adjacent parallel surfaces which are not co-planar, each support housing (17, 16) being mounted on its said wheel means (21) in such manner that the latter