Broadleaf Weed Control in Cool Season Lawns

This publication is intended primarily for non-professionals (homeowners, hobbyists) who manage cool-season turfgrass lawns. Lawns in the northern United States are typically comprised of cool-season turfgrasses. This publication will discuss broadleaf weeds, a term applied to non-grasses (mostly plants classified as dicots), including dandelion, clover, and many others. For information on controlling crabgrass, a grass weed, see FS1308: Crabgrass Control in Lawns for Homeowners in the Northern US. If you are a professional interested in learning more about broadleaf weed control, see the Turfgrass Weed Control for Professionals Guide available at the Purdue University Bookstore (co-edited by Rutgers University).

What is a Weed?

A weed can be simply defined as a plant out of place. It's up to each individual to determine whether a plant is wanted. The preferred vegetation in a lawn is typically mixtures of tall fescue, Kentucky bluegrass, perennial ryegrass, and certain fine fescue species. These grasses are perennials, naturally well-adapted, and further improved through plant breeding to persist for many years and provide living cover to under foot traffic and pets enjoying the lawn. Perennial turfgrasses provide many benefits including preventing soil erosion, improving air quality, and creating a cooling effect during warm weather.

There is important interest in increasing plant diversity within lawns to include broadleaves such as clover to support pollinators. Much like clovers are often incorporated into pastures, white clover and dwarf white clovers (e.g., Microclover) can be incorporated into lawns to complement turfgrass. But managing broadleaf weeds in a mixed lawn is extremely difficult. Hand weeding is the most reliable technique available to selectively remove broadleaf species and protect clovers. Using the herbicide 2,4-D alone is a possible strategy as 2,4-D is only somewhat toxic to clover but will control many other weeds, including dandelion and plantains. However, this strategy has received only limited research and is outside the scope of this publication.

The Importance of a Dense Lawn

The amount and type of broadleaf weeds found in the lawn are greatly influenced by mowing and other aspects of lawn management. Mowing at the higher end of the recommended range for the turfgrass species in your lawn (3" to 4" for most species) and fertilizing with nitrogen as needed to maintain a full canopy is the best way to prevent broadleaf weeds from establishing. Managing diseases such as brown patch that can thin the canopy and allow weeds to establish from seed is also important. Low mowing, too little nitrogen, or poor soil are common issues that result in a thin lawn which allows weed seedlings to establish. Other conditions such as poor drainage and heavy shade favor weeds such as ground ivy, while compacted sites favor prostrate knotweed and low nitrogen inputs favor legumes like clover (Figure 1).

Correcting improper management practices to maintain a dense, vigorous turf in combination with controlling the existing weeds is a primary and lasting method for broadleaf weed control. Of particular importance are proper fertilization, mowing, and watering. Herbicides should be considered an aid, but not a cure, for broadleaf weed problems in lawns. For more information on proper mowing, fertilization, watering, etc., see FS102: Your Lawn and its Care

Weed Life Cycles, Identification, and Management

It is important to properly identify the weed(s) that are problematic and know their life cycle before deciding on a control strategy. For example, weeds with an annual life cycle emerge from seed, grow vegetatively, flower, set seed and then die in less than one year. Controlling annual weeds near the end of their life cycle (after seed set) may not be worth the effort. Winter annual weeds typically germinate in autumn and die in the spring, while summer annual weeds germinate in spring or summer and die at the first frost in autumn. Contrast this with perennial weeds such as dandelion and white clover that may go dormant during certain periods of year but will persist for many years without intervention. These weeds need to be controlled with herbicides or removed by hand (i.e. pulled or dug). The best times of year to control most broadleaf weeds in New Jersey are fall (especially late September through October) or spring (especially May).

Proper identification of the weeds is essential before the most economical and effective herbicide is selected. Suggested resources for weed identification include the New Jersey Weed Gallery, the Virginia Tech University Weed Identification Website and the book, Weeds of the Northeast, Second Edition. Smartphone applications that can identify weeds from a photograph are becoming increasingly accurate, especially for broadleaf weeds. Taking the plant name from these applications and then searching online for more photos of that plant to compare is a good way to verify accuracy.

Herbicides that can selectively control broadleaf weeds in lawns usually contain two to four active ingredients such as 2,4-D, dicamba, MCPA, MCPP (mecoprop), and triclopyr. Products with these active ingredients often have an image of a dandelion on the bottle. These products should explicitly state that they only control weeds and do not kill lawn grasses. Products that contain active ingredients such as glyphosate, glufosinate, fluazifop, and diquat are NOT safe for lawn grasses.

Common Broadleaf Weeds and Control by Season

Spring

As we emerge from winter, winter annual weeds such as henbit, purple deadnettle, hairy bittercress, and common chickweed are most noticeable because as winter annual weeds they begin to flower in late March through April (Figure 2). The presence of these weeds is usually a sign of a thin lawn as these weeds begin their life cycle from seed each fall and the seedlings typically do not survive in a dense lawn. Improving the density of the lawn before the next crop of seedlings emerges in late summer or early fall should be a priority if these weeds are widespread. These weeds can be easily controlled with most products available for broadleaf control in lawns if they are treated in the fall, but are difficult to control at maturity in the spring. Also consider that they die by mid spring and may not be worth the effort to control. Exceptions are mouseear chickweed and speedwells, which tend to persist into late spring or even summer. However, speedwells are difficult to control with most herbicides; products that contain triclopyr are best.

By around mid-April in New Jersey, dandelions begin to flower. Dandelions are a perennial easily controlled by 2,4-D, which is found in most products available for broadleaf weed control in lawns. Pulling or digging dandelions is difficult because of the deep taproot. If part of the upper taproot is left behind, they will regrow. If dandelions are widespread in the lawn each year, even after treating with herbicide, this is an indicator that improving lawn density should be a priority. Dandelions, like winter annuals, readily establish from seed in thin lawns (Figure 3).

Many clovers and other legumes begin to flower in mid to late spring (Figure 4). White clover and woodsorrels (Oxalis spp.) are the most common perennials, while large and small hop clover are winter annuals and black medic is a summer annual, flowering in summer. White clover is the most common legume and patches of clover in the lawn expand by runners (stolons). Dicamba is a common component of most products available for broadleaf weed control in lawns that will provide clover control. Herbicides that contain the active ingredient triclopyr are most effective against clover and woodsorrel. These products are often branded to indicate they control clover, woodsorrel, and or oxalis. Products marketed for crabgrass control often contain the active ingredient quinclorac which is another easily accessible option for effective white clover control, but keep in mind quinclorac will not control woodsorrel. Clovers and other legumes may require two herbicide applications on a 4 to 6-week interval for control, especially if you are not using a product that contains triclopyr or quinclorac.

Perennial broadleaf weeds are usually noticeable by mid-spring, including plantains, mock strawberry, ground ivy, and violets (Figure 5). Plantains can be easily controlled with products that contain 2,4-D, but other weeds such as ground ivy and violets will probably not be killed. Similar to clover, herbicides that contain triclopyr are much more effective against ground ivy and violets.

Summer

Perennials already mentioned will typically survive through the summer. Especially in a dry summer, spurges may become prevalent particularly where the lawn is thin. Spurges are summer annual weeds that often germinate in June and July, setting seed in late summer. Purslane is another summer annual that thrives in thin turf, more commonly in wet conditions or if soil was recently disturbed (Figure 6). Spurges and purslane germinate much later than other summer annual weeds. Herbicides that contain 2,4-D alone or in combination with other herbicides generally provide excellent purslane control. Spurges are more difficult to control, and products labeled for broadleaf weed control that contain two or three of 2,4-D, dicamba, and triclopyr can be effective, but two applications may be needed.

Fall

September through October is an excellent time to combine herbicides and practices to improve lawn canopy density for long lasting weed control. The temperatures of September and October are conducive to improve lawn canopy density with fertilization with nitrogen or seeding. Improving canopy density should be a focus, especially if the aforementioned winter or summer annual weeds were problematic or if weeds such as dandelion continue to be a major problem after being controlled within the last year.

Late Fall through Late Winter

Perennial lillies such as wild garlic, wild onion, and star-of-bethlehem are obvious as they emerge from bulbs (Figure 7). They are ephemeral and usually only conspicuous for a few weeks in late winter until the lawn begins to grow. Sometimes these species are planted intentionally in lawns for their flowers in late winter/early spring, and their presence is not detrimental to the lawn. Products that contain 2,4-D, mecoprop, or dicamba are the best option for wild onion and garlic, but unless repeated applications are made, they usually only provide moderate long-term control due to the hardy underground bulbs. Digging to remove bulbs a more effective but time intensive option for control. Spot treatment with the nonselective herbicide glyphosate is an option, but glyphosate spray kills desirable plants or grass. Even the most careful application often kills lawn grasses around the treated area.

Other Things to Know

'Weed and Feed' Products

Combination products that contain fertilizer and herbicide for broadleaf weed control are widely available in garden stores in the spring. Often marketed as 'weed and feed' or similar, the fertilizer granules also contain herbicide for broadleaf weed control and should be applied in the morning to wet foliage. Generally, sprayable products are preferred to 'weed and feed' products as they can be spot treated only where there are weeds (whereas 'weed and feed' products are applied to the entire lawn), often dramatically reducing the amount of herbicide applied to the lawn. In our research these products are typically less effective than sprayable products, especially for tough-to-control weeds like clover. Another precaution is to ensure the prills do not contact ornamental plants, particularly when applying with a rotary spreader.

Alternative Herbicides

Organic herbicides currently available will kill any plant leaves they contact and are considered non-selective. There are currently no selective organic herbicide options that kill only broadleaf weeds without harming lawn grasses. Also, these organic products are not systemic which means they do not move to growing points (meristems). While these products may control weed seedlings, most weeds recover a week or two after the application. Chelated iron products are an alternative to traditional synthetic products and are selective, meaning they are effective against many broadleaf weeds and safe to the grass. Similar to organic herbicides, chelated iron is non-systemic and multiple applications 2 to 4 weeks apart are needed for weed control. Chelated iron is a synthetic product registered as a biopesticide, but it is not organic (OMRI approved). Our research found multiple applications of chelated iron controlled white clover, but was less effective against dandelion, which recovered from the taproot. Corn gluten meal products are not effective for broadleaf weed control.

Precautions

Read and follow label directions carefully before applying any herbicide.

Avoid applying herbicides when plants are wilting from drought or when high temperatures are expected. Consult the label as most products suggest avoiding applications when temperatures are higher than 85 °F.

Use caution when applying these products around ornamental plants and especially vegetable gardens. Applying on a windy day can result in spray particles drifting onto these plants which are very sensitive to small amounts of herbicide.

Refer to the product label for details when applying herbicides within tree driplines, especially products that contain dicamba.

Do not use any of these herbicides on newly-seeded turf. Product labels usually recommend waiting until the new lawn has been mowed at least three times before treating (usually about 6 to 8 weeks after seeding).

Thoroughly clean the sprayer tank, hose, and boom after using herbicides, especially if the same sprayer will also be used for ornamentals. Ideally one sprayer should be used for turf and another for ornamentals. Do not allow spray mixtures to spill or leak onto areas where they can be taken up by foliage, roots of trees, or ornamentals.

Getting 'Into the Weeds' on Herbicide Active Ingredients

Products that combine herbicide active ingredients are very common. These mixture products control a broader range of weeds than single herbicides. Commonly used herbicide mixtures include 2,4-D, MCPP (mecoprop), MCPA, and dicamba. These herbicides will successfully control many broadleaf weeds. The strengths and weaknesses of various herbicide active ingredients are listed below.

2,4-D is widely used and provides broad spectrum weed control in turfgrass. It is particularly effective for control of weeds with taproots such as dandelion as well as non-taproot species such as plantains. Some weeds not controlled well by 2,4-D are white clover, chickweed, purslane, and ground ivy. While 2,4-D alone provides excellent plantain and dandelion control, it is typically mixed with herbicides such as MCPA, MCPP, and dicamba. The combination of active ingredients work together to provide better weed control than can be provided by one active ingredient alone.

MCPA is chemically-related to 2,4-D and may be used with 2,4-D in prepackaged mixtures. MCPA is not a broad spectrum herbicide and its use alone (i.e., not mixed with another herbicide) is not usually recommended.

MCPP (mecoprop) is most effective in the control of several perennial or winter annual weeds such as chickweed and clovers. MCPA or MCPP are often mixed with 2,4-D and dicamba. Products that contain MCPP are usually more effective than those that contain MCPA.

Dicamba controls many different weeds, several of them are not easily controlled by 2,4-D, MCPP, and MCPA. Of particular importance are the summer annual weeds that have a prostrate growth habit, including knotweed, purslane, and spurge as well as winter annual henbit and chickweeds. Dicamba however, does not control plantains or dandelion.

Triclopyr controls weeds not easily controlled by the above herbicides, including speedwells, lespedezas, woodsorrel (oxalis), ground ivy, violets, and clovers.

Isoxaben can be used primarily in the early fall for preemergence control of numerous winter annuals (especially henbit and common chickweed) and some perennial broadleaf weeds. It will not control emerged broadleaf weeds.

Quinclorac is sold in products marketed for crabgrass control, but it effectively controls a few broadleaf weed species including white clover and speedwells.

Carfentrazone and sulfentrazone are non-systemic, quick acting herbicides that will cause rapid desiccation of the foliage of many broadleaf weed species. They are typically sold in combination with systemic herbicides such as 2,4-D, MCPP, and dicamba.

References

• Joseph C. Neal, Richard H. Uva, Joseph M. Ditomaso. Weeds of the Northeast, Second Edition. 2023. Cornell University Press.

Acknowledgement

This publication was developed using excerpts from the former RCE publication FS385 written by Dr. Steven Hart.

April 2025