Pests are organisms that either damage plants we want or compete with them. Weeds, for example, are hardy plants that can outcompete the weaker species we want to cultivate, while fungal diseases can destroy vulnerable plants in gardens or in agriculture.

Types
Pesticide is a broader term that encompasses all chemical agents intended to control or destroy any kind of pest. There are three types of pesticides--herbicides, fungicides and insecticides.

Function
The main distinction between herbicides and fungicides is their intended function. Herbicides kill weeds or undesirable plants, while fungicides kill or control fungi that can cause fungal disease. Glyphosate and atrazine are common herbicides, while benomyl and propineb are examples of fungicides.

Considerations
Just like other pesticides, some herbicides and fungicides are designed to be somewhat selective and others are broad-spectrum and act against a wide variety of organisms. As noted by the Environmental Protection Agency, most pesticides can cause harm to humans or other animals if used improperly. You should always handle them with caution.

From Network Resources