Selective herbicides kill only certain weeds, while nonselective herbicides kill any green, growing plant, whether it's a weed or not. Most broadleaf herbicides, including products like Weed-Away and Weed Warrior, are systemic and selective to kill broadleaf weeds only. They won't kill weedy grasses.

How does herbicide not kill grass?

Since the enzymes responsible for cell growth in broad-leafed plants are different from the enzymes responsible for grassy plants, herbicides target and disrupt the enzymes in weeds while leaving grass enzymes alone. This ultimately destroys all the weeds without causing any harm to the lawn grass.

How do herbicides kill weeds but not grass?

They vary in the types of weed they kill, the most common being broad-leafed plants while leaving grassy plants unscathed. Herbicides work by inhibiting the growth of cells in the plant. They do this by targeting the enzymes responsible for fat formation thereby halting the development of the cells.