Which term describes substances used to control weeds?

The term that describes substances used to control weeds is 'herbicide.' Herbicides are specifically formulated chemicals designed to target and kill unwanted plants, commonly known as weeds. They work through different modes of action, affecting various plant processes such as growth, photosynthesis, or cell division.

In contrast, insecticides are designed to control insect pests, nematicides target nematodes (roundworms), and pesticides is a broader category that encompasses both herbicides and insecticides, as well as substances used against fungi and other pests. Therefore, 'herbicide' is the precise term for substances focused on weed management, highlighting its importance in agricultural and landscape maintenance practices.