Cooperative Extension Fact Sheet FS385 | July 2003
The presence of broadleaf weeds not only reduces the aesthetic quality of the turf, but more importantly they compete with the desired turfgrass for water, nutrients, and light. Failure to control these weeds often results in a deterioration of the turfgrass stand over time. Broadleaf weed infestations are often symptomatic of a more basic cultural or soil problem in many cases. If these problems persist, weeds also will be a continuous problem. Thus, a sound weed management strategy not only includes removal of existing weeds, but also using corrective management measures for the factors causing poor quality turfgrass.
The numbers and types of broadleaf weeds found in turfgrass are greatly influenced by management and cultural practices. For example, close mowing and too little nitrogen favor white clover. Close mowing also favors weeds such as carpetweed, spurge, plantains, and dandelion. Poorly drained areas favor weeds such as ground ivy, while compacted sites favor knotweed and plaintains.
Correcting improper management practices to maintain a dense, vigorous turf is the best and most lasting method for broadleaf weed control. Of particular importance are proper fertilization, mowing, and watering. Several broadleaf weed species cannot be satisfactorily controlled with proper use of herbicides, further increasing the importance of proper cultural management to reduce the opportunity for their establishment and spread. Herbicides should be considered an aid, but not a cure, for broadleaf weed problems in landscaped turf.
In turf where broadleaf weeds have become a problem, application of an effective herbicide may be necessary for their removal so that the turf can be improved through better management and cultural practices. Several herbicides are available for broadleaf weed control, but weeds vary in response to different products. Thus, proper identification of the weeds is essential before the most economical and effective herbicide is selected. Suggested resources for weed identification include "Weeds of the Northeast" by Richard H. Uva, Joseph C. Neal, and Joseph M. Ditomaso available through Comstock Publishing Associates (a division of Cornell University Press). Also, two web sites can be accessed at njaes.rutgers.edu/weeds and turf.rutgers.edu, then click on turfgrass weeds.
Two or more different herbicides are frequently sold as prepackaged mixtures. Most of the materials discussed are sold by several manufacturers, often under different trade names differing in formulation and concentration. Therefore, no rates are presented here. READ and FOLLOW carefully the label directions on the herbicide container. Applying rates too low may result in inadequate control, while applying rates too high may cause turfgrass injury. The following herbicides are available for the selective removal of broadleaf weeds from cool season turfgrasses.
2,4-D is the oldest and most widely used herbicide and provides broad spectrum weed control in turfgrass. This chemical is particularly effective for control of weeds with taproots such as dandelion, broadleaf plantain, mustards, and shepherd's purse. Amine formulations are most commonly used. However, the low volatile ester form of 2,4-D is often recommended for control of wild garlic and wild onion. Some weeds not controlled well by 2,4-D are white clover, chickweed, purslane, and ground ivy.
MCPA is chemically-related to 2,4-D and may be used as a substitute for 2,4-D in prepackaged mixtures. MCPA is not a broad spectrum herbicide as is 2,4-D and its use alone (i.e., not mixed with another herbicide) is not usually recommended.
MCPP is most effective in the control of several perennial or winter annual weeds such as chickweed and clovers. Dicamba controls many different weeds, several of them are not easily controlled by 2,4-D or MCPP. Of particular importance are the summer annual weeds that have a prostrate growth habit, including knotweed, purslane, and spurge. Dicamba however, does not control plaintains.
Dichlorprop (2,4-DP) and Triclopyr are sold in prepackaged mixtures with 2,4-D and provide broad spectrum weed control.
Triclopyr + Clopyralid is a non-phenoxy, prepackaged mixture sold only under the trade name of Confront. This mix also provides broad spectrum control of many common broadleaf weeds including oxalis. Clopyralid is now available alone under the trade name of Lontrel. Recently, several companies have started to sell herbicide combinations containing triclopyr and/or clopyralid
Isoxaben is sold only under the trade name of Gallery, and is used primarily in the early fall for preemergence control of numerous winter annuals (especially henbit and common chickweed) and some perennial broadleaf weeds. It has no postermergence activity on emerged broadleaf weeds. Delay over-seeding for at least 60 days following application.
Quinclorac is sold only under the trade name of Drive. It effectively controls a few broadleaf weed species including white clover and corn speedwell, but the primary use of quinclorac will be for postemergence crabgrass control.
Chlorsulfuron and Metsulfuron are sold under the trade names of Corsair and Manor, respectively. Both herbicides are labeled for use (in some cases as a spot treatment only) on a limited number of cool season turf species (primarily Kentucky bluegrass). Both herbicides will kill perennial ryegrass and chlorsulfuron will kill tall fescue.
Carfentrazone is a quick acting herbicide that will cause rapid desiccation of the foliage of many broadleaf weed species. It will only be sold in combination with other herbicides such as 2,4-D, MCPP and dicamba.
The use of mixtures of the above-mentioned herbicides is very common. Combination products result in the control of a broader range of weeds than single herbicides. Some herbicide mixtures may effectively control certain weeds that cannot be easily controlled by the individual herbicides used alone. Some commonly used herbicide mixtures are: 2,4-D + MCPP; 2,4-D + dicamba; 2,4-D (or MCPA) + MCPP + dicamba; 2,4-D + dichlorprop; 2,4-D + triclopyr and clopyralid + triclopyr. These herbicides will successfully control many broadleaf weeds found in cool season turf. Listed in the table on page 3 are several weed species and their susceptibility to the most common turf herbicides. The best times of year to control most broadleaf weeds are fall (especially late September) or spring (especially May).
To use these herbicides effectively for broadleaf weed control in turf, remember several points:
|Weed||Response to Herbicide(s)|
|CLOVER, WHITE AND HOP||R||S||S||S||S-I||S||S||S|
|DOCK, BROADLEAF & CURLY||I||I-R||S||I||I||I||S||S|
|KNAWEL (German Moss)||R||I||S||I||S||S-I||S||S|
|SPURGE, SPOTTED OR PROSTRATE**||I-R||I||S-I||S-I||S||S||S||S|
RESPONSE: R= Resistant (i.e. not susceptible to the herbicide), S = Susceptible, I = Intermediate (retreatment may be necessary).
* Some weed species can be controlled by a fall applied, preemergence herbicide such as isoxaben.
** Weeds are most susceptible when immature; mature weeds often require two or more treatments on a 21 to 28 day interval in the spring an/or autumn.
1999 Agronomy Mimeo 79. University of Maryland.
Rutgers, the State University of New Jersey Turfgrass Weed Control Research.
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