Which of the following is a type of herbicide?

Pre-emergent herbicides are specifically formulated to control weed growth by targeting seeds before they germinate. They create a chemical barrier in the soil that inhibits the growth of weed seeds, effectively preventing them from establishing themselves. This type of herbicide is often applied prior to the expected emergence of weeds, making it a valuable tool in integrated pest management and agricultural practices.

In contrast, insecticides are used to control insect pests, fungicides target fungal diseases, and soil amendments are materials added to soil to improve its physical or chemical properties. Thus, the distinct role of pre-emergent herbicides in weed management makes it the correct answer, as it is the only item listed that specifically pertains to the control of unwanted plant growth.