Abstract: A device and method for precisely spraying quantities of pesticides or other chemicals or fluids with little waste is disclosed. The invention includes dual tanks, one each for the concentrated fluid (typically pesticide) and diluting agent (typically water), and a means for automatically mixing their contents downstream of the tanks during the spraying operation. Variable pressure controls, fluid flow rate monitoring devices, and a finely-gauged injection means such as a hollow needle allow for precise mixing of the two fluids contained in the tanks, making the sprayer useful for applying biological control agents as well.