no. 3.100

Broadleaf Weed Control in Lawns

Quick Facts...

Figure 1: Purslane.

Figure 2: Common chickweed.

• For a healthy lawn, plant the best-adapted turfgrass species and use accepted turf management practices.
• A totally weed-free lawn is rarely attainable, even with herbicides
• Indiscriminate use of herbicides can cause problems for trees and other landscape plants, is expensive in time and money, and may actually reduce the vigor of the lawn.
• Postemergent herbicides can control broadleaf weeds such as dandelion, clover, thistle and bindweed.

A dense, healthy stand of grass is the best way to reduce broadleaf weeds in home lawns. To achieve a healthy lawn, plant the best-adapted turfgrass species and use accepted turf management practices (see fact sheet 7.202, Lawn Care). Even with proper management, however, the best-cared-for lawns can still be invaded by troublesome broadleaf weeds. These may require the careful and selective use of broadleaf weed control herbicides.

A totally weed-free lawn is rarely attainable, even with herbicides. It is better to maintain a healthy lawn and tolerate a few weeds rather than to make many applications of herbicides in an attempt to eliminate all weeds. Indiscriminate use of herbicides can cause problems for trees and other landscape plants, is expensive in time and money, and may actually reduce the vigor of the lawn.

Postemergent Herbicides

Postemergent herbicides can control existing broadleaf weeds such as dandelion, clover, thistle and bindweed. Postemergent herbicides do not prevent weed seeds from germinating and reinfesting a lawn.

Once the herbicide kills existing weeds, use good cultural practices (proper fertilization, mowing and irrigation) to encourage rapid fill-in of the turf. Otherwise, new weeds will quickly reinfest the bare soil left open by the recently killed weeds. For this reason, use herbicides as only one tool in the total weed control program.

Which Herbicide Do I Use?

Figure 3: Dandelion.

Figure 4: Field Bindweed.

Before using a postemergent herbicide for broadleaf weed control, identify the weed(s) you want to control. Not all weed species are easily controlled by the same herbicides. You may need to use a combination of two or more herbicides to control specific weeds.

If you cannot identify the weed(s) in question, seek help from your Colorado State University Extension county agent or master Gardeners, Garden centers, or others knowledgeable about turfgrass weeds.

The chemicals most readily available to homeowners for selective postemergent control of broadleaf weeds include 2,4- D, 2,4-DP, MCPP, MCPA and dicamba. They are available singly and in various combinations with each other. Combination products are recommended for difficult-to-control weeds or when several weed species are present in the lawn. All are available in liquid formulations (sprayable) and often in granular formulations (generally with a fertilizer) that can be applied with a drop or broadcast spreader.

All of the chemicals listed above are safe for use on Kentucky bluegrass, perennial ryegrass, tall fescue and fine fescue lawns if you follow the directions on the label. Buffalograss and blue grama lawns that have greened up can be discolored or injured by summer applications of products containing 2,4-D, MCPP, MCPA or dicamba. Spring or fall applications to dormant buffalograss and blue grama lawns are safer, as long as you closely follow label directions.

When Do I Apply?

Applications of herbicides intended for postemergent broadleaf weed control kill only those weeds already present when the herbicide is applied. They do not prevent weed seeds from germinating and developing in the lawn at a later date.

For effective control, weeds must be actively growing when the herbicides are applied. Make spring applications from mid-April through early June, and fall applications in September and October. Applications during July and August are strongly discouraged because weed control is often poor and there is an increased risk of causing damage or discoloration to the lawn, as well as to trees, shrubs, flowers and vegetables.

How Do I Apply?

Liquid and granular formulations of herbicides can be equally effective if they are used properly. Do not apply either if rain is expected within 24 hours of application. For best results, do not mow the turf or water for at least 24 hours following application of either granular or liquid products.

Granular herbicides are the most effective if applied to grass that is moist from morning dew, rainfall or irrigation because the granules adhere to the wet surfaces. Application of granular products to dry turf generally controls few weeds. Be careful when applying herbicides near trees, shrubs, flower beds and vegetable Gardens. Drift from spray applications or misdirected application of granular products can damage or kill these plants. Tree roots can absorb large amounts of herbicides, so be careful applying any herbicide within a tree's root zone, which extends far beyond the tree's "drip line."

In a mature, older landscape, roots of trees and shrubs often occur throughout the entire lawn area. Do not make more than two herbicide applications per growing season on lawns with trees growing in them. Two applications are probably unnecessary for most lawns. Specifically, dicamba may accumulate in the soil with frequent or extensive use and may result in damage to trees, shrubs or other ornamentals.

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