Apparatus producing superheated water and/or steam for weed (36) killing, etc. has diesel fired boiler (30), which, via pump (32), generates hot water at a pressure of 40-52 bar and temperature of 90-115° C. This passes down tube (12) and encounters the constriction provided by nozzle (14). Passing through nozzle (14) into depressurization chamber (16), which is at atmospheric pressure, the water boils. When the super heated water exits ports (20) of distribution pipe (18) it encounters ambient temperature and is transformed into high temperature water vapor and/or water droplets. The apparatus controls or kill weeds (36) using a smaller volume of water and less energy.