There is provided by the present invention an injection system for use in injecting a liquid into a tree, the system comprising: (A) a liquid supply assembly (10) comprising a liquid supply inlet (34) for providing the liquid to the assembly at ambient pressure, an electric pump (68) for pressurizing and discharging the liquid from the assembly at a first pressure above ambient pressure through a liquid supply outlet (36), a pressure switch (72) connected to the supply outlet and in electrical communication with the pump for selectively actuating the pump when the pressure of the liquid supply outlet falls below said first pressure.
