Managing Weeds

The best and most effective way to manage weeds in the lawn is to maintain a thick and healthy lawn. By minimizing sunlight from reaching the soil surface, weed germination decreases. Weeds will find any turfgrass weakness to establish in a lawn. These weaknesses can include improper soil fertility or soil pH, soil compaction, too much or too little water, excessive thatch, and mowing too low for the lawn type. If these cultural problems continue, the weeds will continue to grow.
The first step in weed management is to evaluate the lawn to determine what conditions are causing the weed problems. Start with a soil test to determine the current soil pH and nutrient levels. When soil fertility issues are corrected, eliminate soil compaction and excessive thatch issues. Mowing too low will stress the turfgrass. Raise the mowing height to the correct height for your lawn type. Turfgrass needs 1 inch of irrigation water per week when the grass is actively growing. This includes any rainfall that might occur during the week. The irrigation schedule may be once or twice per week depending on the soil type. Correct any poor soil drainage areas. Weak stands of turfgrass may need to be renovated.
Proper weed identification is important so the correct herbicide may be selected. Herbicides vary in their effectiveness in controlling specific weeds. Some herbicides may not provide any control against the targeted weed. Selecting the wrong herbicide due to misidentifying a weed can result in no control of the weed while wasting money. The Common Weeds and Wildflowers in a great weed identification guide available from Clemson Cooperative Extension Service. Another way to get weeds identified is through your local Extension agent or the Home & Garden Information Center (HGIC). These resources can determine which herbicide will be the most effective based on research data and herbicide label information.
When selecting an herbicide, it must be labeled for both the type of lawn and the weed to be controlled. It is against Federal law to use an herbicide on a lawn or area not listed on the label. The label provides information on weeds controlled, lawn types, mixing procedures, application rates, and proper safety apparel required during mixing and application. Selecting the wrong herbicide or over-applying the correct one is not only illegal, but it can also injure or kill the desirable turfgrass. Remember to read the label for directions on proper and safe application and use. The label is the law.
Warm-season turfgrass (centipedegrass, St. Augustinegrass, bermudagrass, and zoysiagrass) should not have herbicides applied during the spring green-up during March and April. Herbicides applications can severely injure the turfgrass during this time. When temperatures exceed 85F, herbicides should also not be applied. The surfactants can cause injury if applied when it is hot outside. Spray herbicides during cooler days or in the evenings when the temperature has dropped below 85F. Do not spray in the mornings on a day when temperatures will exceed 85F. The hotter temperatures later in the day will cause similar injury as if applying the herbicide during the heat of the day.
Irrigate lawns one to two days prior to herbicide application. This removes drought stress from the turfgrass. If irrigation is not an option, apply herbicides one to two days after a rainfall of one-half inch or more.
Lawns should not be mowed prior to herbicide application. Wait three or four days after mowing before applying herbicides. Also wait two or three days after an herbicide application. The weeds need time to absorb and translocate the herbicide applied down to their root system.
The Lawn Weed Control Timing Chart is available to homeowners and turfgrass professionals to plan the timing of herbicide applications. This chart helps determine if weed issues should be dress immediately, or if herbicide applications should be delayed until later in the season or until the next year to be most effective. Visit the Home and Garden Information Center or to view the Lawn Weed Control Timing Chart.
For more information on lawn weed control, please visit the Home and Garden Information Center website at Tune in on Tuesday nights to watch “Making it Grow” at 7 p.m. on SCETV or Email Outen at
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