Pre-emergent herbicides

Pre-emergent herbicides work into the ground or spray on the ground before the weed seed begins to grow for the season. Typically there are two times of the year to apply pre-emergent herbicides. The first application period is in the spring before the weeds begin to grow for the summer season. The second application is in the fall, which prevents seeds from setting on the weeds.

I recommend: See the discussion of pre-emergent herbicides on the All About Lawns.

Post-emergent herbicides

Post-emergent herbicides work after the plant is green and growing for the summer season. You can spray post-emergent herbicides directly on undesirable weeds.

I recommend: Landscape-America.com offers tips on how to use post-emergent herbicides for dandelion and crabgrass control in lawns.

Contact herbicide

A contact herbicide only kills the part of the plant it comes in contact with. Spraying a contact herbicide on the visible part of the plant only kills the stems and leaves. The roots remain alive and may generate another stem and leaves.

I recommend: Biconet offers an explanation of how its contact herbicide, Scythe, works.

Buffering agent

You may need to add a buffering agent to your herbicide and water mixture to control the pH balance. The amount of buffering agent varies and depends on the type and quantity of herbicide you use.

I recommend: A list of buffering agents used with herbicides is available from Herbicide-Adjuvants.com.

Selective herbicide

A selective herbicide kills only the plants listed on its label. Most selective herbicides kill a list of broadleaf weeds, such as dandelions. A selective herbicide usually doesn't bother other plants in the lawn or field. Read the label to know exactly what the particular herbicide kills.

I recommend: Interstate Products offers a line of selective herbicides.

Non-selective herbicide

A non-selective herbicide kills every plant it comes in contact with. This type of chemical burns down woody bushes as well as green plants.

I recommend: See examples of non-selective herbicides at Professional Pest Control Products.