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What Is Pre-Emergent Herbicide?

grass,lawn image by Greg Pickens from <a href=''></a>

Pre-emergent herbicides are chemicals that prevent germinating weeds in lawns from surviving. They kill weed seedlings as they emerge, but they don't kill seeds. These herbicides must be on the ground before the seeds germinate to be effective.


Pre-emergent herbicides are effective against annual weed grasses, including crabgrass, foxtail, barnyard grass and goose grass. They offer some control of broadleaf weeds, such as spurge, oxalis and purslane.


Apply pre-emergent herbicides in early spring. Apply in March in warm southern climates and in April in cool northern areas.


Effective control without harming the roots of existing lawn grasses depends on a careful application of the right amount of herbicide. Refer to the herbicide label instructions and follow them carefully.


Pre-emergent herbicides must be washed off the grass and onto the soil in order to be effective. Rainfall amounts of 1/2 to 1 inch are sufficient. In the absence of rain, water the lawn with a hose or sprinkler system.


Pre-emergent herbicides kill emerging grass seedlings along with any weeds. Delay seeding a lawn until summer or fall when pre-emergents have been used.

Choose A Pre Emergent Herbicide

Determine what types of weeds grow typically in your yard throughout the summer and fall. Take samples to your local nursery or use an online tool, such as, to help identify the types of weeds in your garden. The common types of weeds will vary by location and local nurseries will be the most familiar with their identification. According to James A. McAfee, Ph.D. at Texas A&M University, pre-emergent herbicides, such as First Down Granules, Crabgrass Preventer, Betasan, and Surflan, will kill many annual grass weeds, while Protrait Braodleaf Weed Preventer is best for chickweed, spotted spurge, and other annual broadleaf weeds. Decide if you want a granule or liquid spray pre-emergent herbicide if there is a choice among the available herbicides. This can be based on personal preference or ease of application to the location.

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