Preemergent Herbicides for Crabgrass Prevention in Lawns
Preemergent herbicides are most effective at controlling annual grassy weeds like crabgrass, foxtail, goose grass, and barnyard grass. Fair control of annual broadleaf weeds such as purslane, spurge, and oxalis can be expected from most preemergents.
Preemergent herbicides kill very young weed seedlings but not seeds, so they must be "in place" prior to weed seed germination to be effective. One half to one inch of water from precipitation or irrigation is needed following application to move the herbicide off foliage and onto the soil surface, where weed seeds are germinating. Preemergent products should be applied during March or early April. Sites that warm earlier in the spring like southern exposures and turf near sidewalks should be treated in early to mid-March. Acceptable weed control and prevention of turf injury require uniform application at correct rates.
Some preemergent herbicides can harm the roots of lawn grasses if excessive rates are applied. A healthy, vigorous turf will enhance the effectiveness of any preemergent herbicide application. Since all preemergent herbicides, except siduron sold as Tupersan, will also kill germinating grass seed, lawn overseeding must be delayed until late summer/early fall when a spring preemergent application is made.
For more information, see the following Colorado State University Extension fact sheet(s).
For more information, see the following Planttalk Colorado™ script(s).
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Updated Friday, October 31, 2014