Recent advances in the knowledge of basic physiological processes, coupled with the discovery of the growth-regulator type of phytocides, have stimulated tremendous interest and work in methods of controlling weed plants. New advances are being made so rapidly that it is difficult for foresters to keep abreast of developments. It seems desirable, therefore, to bring together some of the fundamental concepts of plant physiology as related to weed control. The field worker familiar with basic physiological processes can make most effective use of available tools and methodology. An understanding of the natural annual cycles in reserve foods of weed trees can make control methods more efficient. Information about the fluctuations induced by treatment may be equally as useful. This knowledge can be applied whether the control method is mechanical, chemical, biological, or pyric. Usually, treatment is most effective when the amount and location of reserves render the plant most susceptible to the particular method chosen.