A substance that specifically kills weeds and prevents their growth is called what?

A substance that specifically targets and kills weeds is classified as an herbicide. These chemicals are designed to control unwanted plants by disrupting their growth, photosynthesis, or other biological processes. Herbicides are crucial in agricultural and landscaping practices for managing weeds that compete with crops for nutrients, light, and space.

In contrast, fungicides are used to kill or inhibit the growth of fungi and are intended for controlling plant diseases caused by fungal pathogens. Acaricides are specifically formulated to eliminate mites and ticks, targeting a different group of pests altogether. Finally, the term pesticide encompasses a broader category that includes herbicides, fungicides, insecticides (for insects), and other substances used to eliminate various pests. Since the question specifically asks about a substance that kills weeds, herbicide is the precise term for that function.