Just as pesticide is used to rid an area of unwanted pests, herbicide is used to get rid of unwanted plant life. Unwanted plants include weeds, brush, unproductive bushes or trees, and other growth that takes nutrients away from crops and other useful plants. Many herbicides are synthetic and can be toxic to "good" plants, as well as to animals and humans. While there are organic herbicides, it is important to read labels carefully to insure that people, pets, livestock and useful vegetation won't be harmed by their use.

Herbicides are available in two main types: nonselective and selective. A nonselective herbicide is used to kill all growth and is generally reserved for agricultural use or for clearing large or heavily overgrown areas. On the other hand, a selective herbicide is used to target certain types of plant life. This form works to curb growth, usually through some type of hormone disruption, and should not effect other vegetation.

For the home gardener, nonselective herbicide is rarely required. An organic, selective herbicide is the better choice for maintaining grass and home gardens. Farmers, orchard owners, developers and park services may use nonselective forms to treat large areas and prepare land for future use.

One problem with using a selective herbicide is that it can create resistant species of weeds and parasitic vegetation. Herbicide effectively kills most weeds of the particular type is used against, but at least a few plants generally survive. Those that survive can produce resistant offspring.

To avoid resistance, it is best to use more than one type of herbicide against each specific plant. This can get tricky when attempting to protect some plants while getting rid of others. The best way to avoid resistance, especially with plants that are annuals, is to use herbicide only as recommended and only when absolutely needed. Also, it is a good idea to use one type of herbicide during the first application, and another at the next interval so the unwanted plants won't build up an immunity to one particular type.