Weed Killer Mode of Action
Contact weed killers (e.g. Weed Weapon Natural Power ) cause damage wherever they touch a plant. To work well, a contact weed killer should thoroughly cover the leaves and stems. Contact weed killers work best on small annual weeds. They have less effect on perennial weeds unless applications are repeated. Most contact weed killers work very quickly (1-3 days).
Systemic weed killers (e.g. Weed Weapon Extra Strength ) are absorbed and moved throughout the plant. They are sometimes applied to the foliage and sometimes to the soil although some systemic weedkillers such as glyphosate in Weed Weapon Extra Strength are inactivated by contact with clay particles in the soil. They can be absorbed and translocated (moved) from the foliage, roots or stems to other parts of the plant.
Systemic herbicides work well on perennial weeds because the herbicide is moved to parts of the plant other than where it was applied. This feature is particularly valuable for killing root, tuber and rhizome growth on perennial weeds.
Weed Weapon Rapid Action combines both contact and systemic action giving the fastest effects on weeds and still killing down tot he roots.