Weed species are frequently difficult to control because they store food reserves in their root systems or underground storage structures. Controlling only what is above ground is usually not sufficient for satisfactory, long-term control; what is underground must be controlled as well. Translocated herbicides (those that can move into the roots) are usually the most effective chemical option to control perennial weeds, but when they are applied is very important. In the spring, perennials rely on stored food reserves to initiate new growth, so most of the food at this time of year is moving upward from the roots to support new vegetative development. Because of this upward movement, it’s often difficult to get sufficient herbicide into the root when applications are made in early spring. Better control of perennial broadleaf species can be achieved when postemergence translocated herbicides are applied about the time the plants begin to flower. Another good time to treat perennial weed species is early to midfall. As day length shortens and temperatures fall, perennial plant species begin to move food back into their roots, and more translocated herbicide moves to the root as well.