The development and maintenance of a dense, healthy stand of grass is the best way to reduce the incidence of broadleaf weed problems developing in home lawns. To facilitate the production of healthy lawns, homeowners should incorporate recommended turfgrass selections and management practices into their establishment and maintenance programs. These recommendations include the use of adapted species and cultivars, adequate fertilization programs, proper mowing practices, adequate supplemental irrigation, and necessary insect and disease control measures. Occasionally however, even the best cared-for lawns are sometimes invaded by broadleaf weeds. To have a completely weed-free lawn, the homeowner may have to resort to the careful and selective use of braodleaf weed control herbicides.
POSTEMERGENT HERBICIDES can be used to control broadleaf weeds (i.e., non-grassy weeds) that are not prevented with the use of preemergent herbicides. It is essential that sensible cultural practices be used to encourage rapid fill-in soon after the turf has been treated with the weed control chemical, since new weeds will quickly reinfest the areas left open by the recently-killed weeds. For this reason, HERBICIDE USE SHOULD BE REGARDED AS ONLY ONE TOOL IN THE TOTAL WEED CONTROL PROGRAM.
WHICH HERBICIDE TO USE? Before using a postemergent herbicide for broadleaf weed control, it is important to identify the weed(s) which you are attempting to control. The reason is that not all weed species are controlled via the use of one specific herbicide. The homeowner may need to use a combination of two or more herbicides to obtain the desired control. If you can not identify the weed(s) in question, seek help from garden center personnel, your county Extension agent, or from the Plant Pest Diagnostic Clinic (The Ohio State University campus; 614/292- 5006).
The most readily available chemicals to homeowners for selective, postemergent control of broadleaf weeds include: 2,4- D, 2,4-DP, MCPP, and dicamba. These chemicals are available alone, and in various combinations with each other. Combination products are recommended for difficult-to-control weeds or when a variety of weed species is present in the lawn. All are available in liquid formulations (sprayable), and often in granular formulations (generally with a fertilizer) which 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 THE DIRECTIONS ON THE LABEL ARE FOLLOWED. MCPP is the safest of the listed herbicides to use on bentgrass lawns.
WHEN TO APPLY? Applications of herbicides intended for postemergent broadleaf weed control will only kill those weeds present at the time that the herbicide is applied. They DO NOT prevent weed seeds from germinating and developing in the lawn at a later date. It is also important to remember weeds must be actively growing when the herbicides are applied so effective control can be achieved. This means that spring applications should be made from mid-April through early June, and fall applications should be made during the months of September and October. Herbicide applications during July and August are strongly discouraged because not only will weed control be more difficult to achieve but also an increased risk of causing damage/ discoloration to the lawn.
HOW TO APPLY? Liquid and granular formulations of herbicides can be equally effective if they are used properly. Neither should be applied if rain is expected within 24 hours of application. For best results, the turf should NOT be mowed or watered for at least 24 hours following application of either granular or liquid products. Granular herbicides will be most effective if applied to grass that is moist (from morning dew, rainfall, or irrigation) because the granules will adhere to the wet surfaces of the weeds.
Care should always be exercised when applying herbicides near trees, shrubs, flowerbeds, and vegetable gardens. Drift from spray applications or misdirected application of granular products can result in damage or death of these plants. It is important that dicamba NOT be applied within the dripline of trees or shrubs. Dicamba can be root absorbed by these plants, possibly resulting in damage.
|Weed Control||Life Cycle(1)||Recommended Chemical(2)||Time of Application||Degree of Control|
|Bindweed||P||2,4-D ester or dicamba(4)||early summer||good|
|Black medic||A||dicamba(4)||early spring||good|
|Chickweed, common||A||MCPP or dicamba(4)||spring or fall||good|
|Chickweed, mouse-ear||P||MCPP or dicamba(4)||fall or spring||good|
|Cinquefoil||P||2,4-D||fall or spring||good|
|Dandelion||P||2,4-D or dicamba(4)||fall or spring||good|
|Dock, curly||B||2,4-D or dicamba(4)||fall or spring||good|
|Garlic or onion||P||2,4-D ester||late fall, early spring||fair|
|Ground ivy||P||dicamba(4,6)||summer, fall or spring||fair-good|
|Knotweed||A||dicamba(4,6)||spring to mid-summer||good|
|Pigweed||A||2,4-D or MCPP||summer||good|
|Plantain, buckhorn||P||2,4-D or MCPP||fall or spring||fair|
|Plantain, common||P||2,4-D or MCPP||fall or spring||good|
|Poison ivy||P||Amitrol-T or Roundup(5)||spring or summer||good|
|Purslane||A||dicamba(4)||spring or fall||good|
|Red sorrel||P||dicamba(4)||spring, summer or fall||good|
|Speedwell, creeping||P||2,4-D, MCPP or Dicamba||fall or spring||good|
|Speedwell, annual||A||dacthal||spring or fall||fair|
|Spurge, spotted||A||dicamba(4,6) or MCPP||summer||fair-good|
|Sow thistle||A||2,4-D or dicamba(4)||fall||good|
|Wild violet||P||dicamba(4,6) or triclopyr||spring or fall||fair-good|
|White clover||P||MCPP or dicamba(4)||spring, summer or fall||good|
|Wild carrot||B||2,4-D or dicamba(4)||fall or spring||good|
|A||2,4-D ester, MCPP or dicamba(4,6)||early summer||fair-good|
(1) A = Annual, B = Biennial, P = Perennial.
(2) Do not use 2,4-D on golf course greens and use with caution on other bentgrass turf.
(3) Three or more applications may be necessary to eradicate thistle.
(4) Dicamba may accumulate in the soil with frequent or extensive use which may result in damage to trees, shrubs, or other ornamentals.
(5) Nonselective herbicides. Spot treat only.
(6) 2,4-D plus dichlorprop (Weedone formulations) 2,4-D plus triclopyr (Turflon formulations) and triclopyr plus clopyralid (Confront) are effective combinations for many broadleaf weeds, including hard-to-control species such as ground ivy, wood sorrel (oxalis), spotted spurge and wild violets.
William E. Pound
John R. Street
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868