A __________ is any chemical used to control pests.

The term that best fits the definition of any chemical used to control pests is "pesticide." Pesticides encompass a wide range of chemical substances designed to deter, kill, or manage pest populations including insects, weeds, fungi, and other pests that can harm humans, agriculture, or the environment. This category includes specific types of pesticides such as insecticides (for insects), herbicides (for weeds), and fungicides (for fungi), but the broader term “pesticide” is what captures all these various chemicals.

While fertilizers are used to promote plant growth and are not designed to control pests, insecticides focus solely on combating insect pests, and herbicides target weed control specifically. Therefore, defining a chemical that controls a wide range of pest types aligns perfectly with the term "pesticide," making it the most appropriate answer in this context.