Which term refers to any chemical substance intended for preventing, destroying, or controlling harmful organisms?

The term you are looking for is "pesticide," which encompasses a broad range of chemical substances aimed at preventing, destroying, or controlling harmful organisms. This includes not only insects and fungi but also weeds and other pests that can negatively impact agriculture, public health, and the environment.

While fungicide specifically targets fungi, herbicide is designed to eliminate unwanted plants or weeds, and insecticide focuses on insects, pesticides is the overarching category that includes all these specific types of chemical agents. Therefore, "pesticide" is the most accurate term for a substance intended for managing harmful organisms across various categories.