This paper examines why systemic herbicides may be ineffective, and suggests strategies to improve their performance. Carbohydrates supply energy for plants to initiate growth in the spring and fall, and to ensure plant survival during periods of dormancy in summer and winter. These storage organs also have buds, which contain dormant shoots. If released from dormancy, these buds will initiate growth and re-establish plant stands. Herbicide translocation in plants, however, can be altered by several plant or environmental factors, reducing species control.
Leaves return carbohydrates to roots after stem elongation begins.
Therefore, herbicides, if applied when roots are supplying carbohydrates to leaves, will remain in the leaves. After leaves die, root buds will break dormancy and establish new plants. However, if herbicides are applied to grasses when stems begin to elongate or to legumes when six to eight inches tall, then maximum movement of herbicides to root buds will occur, subsequently increasing control. Seasonal movement of carbohydrates between leaves and roots for a cool season species, as shown by varying levels of carbohydrates in roots over time. Warm season species movement occurs later, with no fall regrowth.