The invention concerns a vehicular device for applying plant treatment agents, with a spraying device and at least one tank (24, 24') for the plant treatment agent and a separate tank for a diluent, and also with at least one metering device (32, 32') for injecting measured quantities of the treatment agent into mixing chambers (31, 31') for mixing with the diluent. The metering devices (32, 32') used in the invention inject the treatment agent into the mixing chambers (31, 31'), into which the diluent is pumped under constant-pressure control (30), only when a given output pressure is exceeded. For each group (6) of spray heads in the sprayer unit (11) and/or for each spraying agent, a reciprocating-piston pump (1) is provided as the metering device (32, 32'). The pumps (1) are driven via electromagnetic transductors (8) at constant piston speed and stroke, and their associated mixing chambers (31, 31') are located in the immediate vicinity of the spray nozzles (2, 3, 4, 5) of a particular group (6) of heads in the sprayer unit (11). The operating frequency of the reciprocating-piston pump (1) is controlled by frequency control of the electromagnetic transductor (8), as a function of the instantaneous speed of travel of the spraying device and the required output and concentration of the treatment agent, by means of a computing and control unit.