Winter Annual Broadleaf Weed Control in Golf Course Turf

As turf begins to greenup this spring, superintendents should begin preparations for controlling annual broadleaf weeds that have established. Scouting turf in winter and early spring is recommended to identify broadleaf weeds that warrant control. Turf managers should also note weeds that were present in previous years and pay particular attention to new species that may have become established. Early detection is critical in preventing the spread of new species, particularly perennial broadleaf weeds, throughout turfgrass areas. Practitioners identifying new species should evaluate turf cultural practices that may require modification to improve integrated pest management. 

Broadleaf weeds like white clover and broadleaf plantain are often problematic in turf grown on soils with nutrient deficiencies, improper pH, poor drainage, or excessive compaction. Turf mowed at heights lower than physiological capacities often have reduced vigor and recuperative capabilities from disease, traffic, heat, shade and other environmental stresses. Broadleaf weeds like chickweed, dandelion and oxalis may thrive under various soil types and site conditions but are often present in turfgrasses under stress. Turf managers should also evaluate turfgrass species and cultivar selection to determine the agronomic suitability in areas where broadleaf weed infestations are significant. 

Broadleaf Herbicide Applications
Herbicides available for broadleaf weed control in turf may differ in efficacy on various species. Herbicide combinations of two or more active ingredients will generally improve the spectrum of weeds controlled and are often sold as prepackaged formulated mixtures. Most broadleaf herbicides are sold by several manufacturers under various trade names that may differ in formulation and concentration, and thus, turf managers should carefully read and follow label directions for specific products.

Superintendents applying herbicides for broadleaf weeds in spring must consider the agronomic impact of environment and application timing on efficacy for weed control and turf safety. Turfgrasses are generally more sensitive to broadleaf herbicides during initial spring growth. Herbicide applications in early spring may inhibit turfgrass growth and delay spring greenup. For example, dicamba is an effective herbicide on many weeds but may significantly discolor creeping bentgrass and St. Augustinegrass in spring. Injury from dicamba may also delay greenup of warm-season turfgrasses from winter dormancy during initial spring growth.

Broadleaf herbicides applied under cool weather in early spring often have reduced efficacy and require sequential treatments to control weeds. Efficacy of broadleaf weed herbicides generally improves when temperatures are consistently in the 70s compared to cooler weather. As temperatures increase in spring, herbicides are absorbed and translocated more effectively as weeds resume active growth. Herbicide applications in late spring may have reduced economic value as winter annual broadleaf weeds begin to senesce from heat stress. Many weeds like chickweed and henbit will be desiccated under heat stress in summer and herbicide applications may not be necessary in late spring.

Herbicide Absorption Influences Efficacy
Broadleaf herbicides are primarily absorbed through foliage of targeted weeds. Turfgrasses are able to metabolically inactivate broadleaf herbicides before the absorbed compound becomes physiologically toxic. Weeds controlled by broadleaf herbicides are generally unable to metabolize applied compounds which lead to selective control in turfgrasses. Foliar absorption levels are important in order for weeds to absorb concentrations necessary to induce injury for control.  

Spray adjuvants may be applied with several of these herbicides to enhance foliar absorption and reduce surface tension on treated leaves. Efficacy of herbicides in early spring may be enhanced for broadleaf weed control by using an adjuvant. For example, metsulfuron (sold as Blade or Manor) is a sulfonylurea herbicide labeled for broadleaf weed control in centipedegrass lawns. Efficacy of sulfonylureas generally increases with temperature but tank-mixing metsulfuron with a non-ionic surfactant in early spring may increase foliar absorption to improve herbicide activity. High quality adjuvants are recommended that contain approximately 80 to 90 percent active ingredient, such as Activator 90 non-ionic surfactant. Although adjuvants may improve weed control, enhanced activity may increase turf injury, and thus, end-users should be cautious when phytotoxicity is a concern. 

Herbicide absorption may also be influenced by growth, maturity and physiological health of broadleaf weeds. Plants under heat stress in late spring may absorb less herbicide compared to unstressed plants which may reduce the relative impact of treatments. Furthermore, stressed weeds with inhibited growth may translocate less material within the plant which may lead to reduced efficacy that require sequential applications. Broadleaf herbicides should only be used on unstressed turf with adequate soil moisture. Turf should not be mowed for at least one day before and after treatments.

Granular products are generally easier to handle and apply with spreaders than sprayable formulations. However, foliar absorption of these products may be more critical compared to liquid formulations. Sprayable applications are generally more effective and provide better coverage over treated areas than granular herbicides applied with spreaders. Most granular postemergence herbicides for broadleaf weed control should be applied in early morning under heavy dew so herbicides may stick to leaves.

Winter Annual Broadleaf Weeds
Winter annual broadleaf weeds germinate in fall or winter and grow actively in spring. As temperatures increase over spring, winter annuals flower, produce seeds and die in summer. Winter annual broadleaf weeds are commonly found on turf that was thinned or weakened from traffic, disease or injury during and fall winter. Turf grown in shade, compacted soils or with poor drainage are prone to broadleaf weed infestations during fall and spring.

Henbit (Lamium amplexicaule L.) is a winter annual weed more commonly found in warm-season than cool-season turfgrasses. Henbit thrives during spring and fall under fertile soils and often has showy pink to purple flowers. Henbit has square, green to purple stems, with rounded to heart-shaped leaves. Purple deadnettle (Lamium purpurem L.) is a winter annual weed found in turf conditions favorable to henbit. Leaves are triangular and less deeply lobed than henbit and flowers are less showy and lighter purple. After henbit and purple deadnettle produce flowers in spring, lifecycles are completed in summer and plants die. Selective control of henbit and purple deadnettle may be achieved with sulfonylureas, such as Manor (metsulfuron) and Monument (trifloxysulfuron). These weeds can also be controlled with combination products such as Trimec Classic (2,4-D + dicamba + MCPP), Speedzone (carfentrazone + 2,4-D + dicamba + MCPP), OneTime (quinclorac + dicamba + MCPP), or Celsius (thiencarbazone + iodosulfuron + dicamba).

Corn speedwell (Veronica arvensis L.) is a winter annual weed common to lawns and landscapes. Corn speedwell reproduces by seed in fall or early spring and forms dense mats in turf. Leaves of mature plants are sparsely hairy, egg-shaped and have rounded teeth on margins. Slender speedwell (Veronica filiformis Sm.) is a creeping perennial with slender stolons. Both speedwells produce light blue flowers in spring while slender speedwell reproduces vegetatively and does not produce viable seed. Speedwells may be controlled with Drive (quinclorac), Monument (trifloxysulfuron), or Manor (metsulfuron). Broadleaf herbicide combinations have activity on speedwells but may require repeat applications for effective control.

Common chichkweed (Stellaria media (L.) Vill.) is a winter annual with prostrate dense patches in turfgrass. Chickweed germinates by seed in spring and fall and is commonly found under shady, moist areas. Chickweed forms small, white flowers with short, lobed petals. Mousear chickweed (Cerastium vulgatum L.) is similar in appearance to common chickweed but is a perennial with oblong, hairy leaves. Superintendents managing turf infested with chickweed in late spring should determine if herbicide applications are economical relative to biological senescence. Chickweed may die out in turf under dry, hot weather during summer months and stems do not persist during summer. Common and mousear chickweed can be controlled with Manor (metsulfuron), Dismiss (sulfentrazone), or mixture products such as Chaser (2,4-D + triclopyr), OneTime (quinclorac + dicamba + MCPP), and Trimec (2,4-D + dicamba + MCPP).

Hairy bittercress (Cardamine hirusta L.) is a winter annual, but occasionally a biennial, found in turf under moist, cool soils. Leaves are pinnate with round to kidney-shaped leaflets and plants have a slender, branched taproot. Bittercress produces small white flowers in spring and reproduces by seed. Two to three-way herbicide mixtures provide excellent control of hairy bittercress in turf. Check labels for turfgrass species safe for applications of these products.

Perennial Broadleaf Weeds in Spring
Perennial broadleaf weeds in spring are more difficult to control than winter annuals due to better heat tolerance and the ability to reproduce by seed or vegetative stems in spring. Postemergence herbicides may be less effective in spring than fall because of active shoot growth and plant allocation of energy from stems to leaves. Simple perennials may have a fleshy taproot at the base of the plant while complex perennials have rhizomes and stolons, or below and aboveground stems, respectively. Herbicides often burn-back shoot growth of perennial weeds but regrowth may occur from vegetative stems that could warrant repeat applications.

White clover (Trifolium repens L.) is a mat-forming perennial with low creeping branched stems that root at the nodes. Plants have trifoliate leaves and white, rounded flowers upon maturity. White clover reproduces by stolons (aboveground stems) and seeds which may germinate throughout spring, summer, and fall. White clover tolerates close mowing, wide ranges of soil acidity, and thrives under moist soils. White clover can be controlled in turfgrasses with Confront (clopyralid + triclopyr), Drive (quinclorac), Manor (metsulfuron), or three way broadleaf mixture products such as Trimec (2,4-D + dicamba + MCCP), Escalade (2,4-D + fluroxypyr + dicamba), or OneTime (quinclorac + dicamba + MCPP).

Common dandelion (Taraxacum officinale Weber in Wiggers) is a perennial broadleaf weed with a basal rosette of leaves with lobed margins. Plants have a thick, long fleshy taproot but may reproduce by seed from late spring to early fall. Mature plants produce yellow flowers on leafless stalks. Dandelion tolerates many turf management practices and is found on a wide range of soil types. Catsear dandelion (Hypochaeris radicata L.) has irregular leaves with rounded lobes. Both common and catsear dandelion have yellow flowers and exude a milky sap from stems when cut. Selective control may be achieved with Confront (clopyralid + triclopyr) Manor (metsulfuron), Monument (trifloxysulfuron), or three way broadleaf mixture products such as Trimec (2,4-D + dicamba + MCCP), Escalade (2,4-D + fluroxypyr + dicamba), or OneTime (quinclorac + dicamba + MCPP).

Broadleaf plantain (Plantago major L.) is a rosette-forming perennial weed commonly found in low to high maintenance turf. Broadleaf plantain forms a short taproot with fibrous roots and reproduces by seed from spring to fall. Leaves are broad oval shaped and plants form long leafless flower-stalks. Buckhorn plantain (Plantago lancelota L.) has narrower leaves than broadleaf plantain and produces a thick taproot. Buckhorn plantain tolerates close mowing, grows on compacted soils and forms seedheads in cone-like spikes. Selective control in turf can be accomplished with aforementioned products for dandelion control. 

Yellow woodsorrel (Oxalis stricta L.) is a clover-like perennial with heart-shaped leaves. Yellow woodsorrel has long, slender rhizomes with secondary fibrous root systems and is commonly found in turf, landscapes, and roadsides. Yellow woodsorrel produces flowers with five yellow petals and grows under various environmental conditions, soils, and management regimes. Selective control may be achieved with two to three way broadleaf mixture products or sulfonylureas such as Certainty (sulfosulfuron), Manor (metsulfuron), and Monument (trifloxysulfuron).

Broadleaf Weed Herbicides for Turfgrass
Broadleaf weed herbicides should not be applied to newly-seeded turf and seedlings should be given approximately six to eight weeks after emergence before treatments. All herbicides have the potential to cause some foliar yellowing but responses to treatments depend on turfgrass species, growth, and maturity.

2,4-D is one of the oldest and most widely used herbicides for broadleaf weed control in turf. 2,4-D provides broad spectrum weed control in turfgrass and is particularly effective for control of weeds with taproots like dandelion, broadleaf plantain, mustards, and shepherd’s purse. Amine formulations are most commonly used but the low volatile ester is often recommended for control of wild garlic and wild onion. Do not use 2,4-D on creeping bentgrass or bermudagrass greens overseeded with roughstalk bluegrass. Some weeds not controlled well by 2,4-D are white clover, chickweed, purslane, and ground ivy.

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. Carfentrazone is found in the combination products of Speed Zone, Power Zone, Quicksilver, and SquareOne. Carfentrezone use on warm-season turf is restricted to bermudagrass and zoysiagrass but can be safely applied to most cool-season turfgrasses. Efficacy for broadleaf weed control is generally more effective in spring and fall compared to summer.

Chlorsulfuron and metsulfuron are sold under the trade names Corsair and Manor (Blade or Spice), respectively. Both herbicides are labeled for use on a limited number of cool season turf species including Kentucky bluegrass and fine fescue. Both herbicides will kill perennial ryegrass and chlorsulfuron controls tall fescue. Chlorsulfuron and metsulfuron can be applied to most warm-season turfgrass but may delay spring greenup when used in early to mid spring. Both herbicides control annual and perennial broadleaf weeds but sequential applications may be required after four to six weeks.

Clopyalid and triclopyr are non-phenoxy herbicides sold together as Confront. This mix also provides broad spectrum control of broadleaf weeds including chickweed, clover, black medic, common cocklebur, beggarweed, false dandelion, henbit and oxalis. Both herbicides can be applied on warm and cool-season turf except creeping bentgrass. Triclopyr should only used on warm-season turfgrasses if moderate injury can be tolerated. Do not apply to triclopyr to bermudagrass unless it is completely dormant.

Dichlorprop (2,4-DP) is sold in pre-packaged mixtures with 2,4-D and effectively controls chickweed, clover, henbit, oxalis, and other winter broadleaf weeds. Dicamba controls many different weeds, several of which are not easily controlled by 2,4-D or MCPP. Dicamba however, does not control plaintains. Dicamba is included in many herbicide combination products and also in some fertilizer and herbicide combinations. Dicamba and other broadleaf herbicides move readily in some soils and can be absorbed by plant roots. Therefore, products containing dicamba should not be used near trees or ornamentals.

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 like 2,4-D and use alone (i.e., not mixed with another herbicide) is not usually recommended. MCPP is most effective in the control of several perennial and winter annual weeds such as clovers and chickweed. Quinclorac is sold only under the trade name 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. Quinclorac is also found in a mixture product called One-Time which contains dicamba and MCPP. One-Time provides excellent control of clovers, dandelion, and other broadleaf weeds.

Trifloxysulfuron is a sulfonylurea herbicide sold as Monument for use on bermudagrass and zoysiagrass only. Trifloxysulfuron should not be used on desirable cool-season turfgrasses but can be used to control ryegrass during spring transition on overseeded bermudagrass. Broadleaf weeds controlled include clover, dandelion, henbit, and oxalis and trifloxysulfuron can be used on grasses, sedges, and kyllinga. It is recommended that a non-ionic surfactant of at least 80% active ingredient be added to the spray solution at 0.25 to 0.5 % v/v. Other surfactants such as methylated seed oil or crop oil concentrate can be effective as well, but may cause temporary turf discoloration.

Katana is a new sulfonylurea herbicide for use in bermudagrass, centipedegrass, and zoysiagrass. Katana contains a new active ingredient, flazasulfuron, and is formulated in a 25 percent dry, flowable formulation. Katana has postemergence activity on numerous broadleaf and grassy weeds including clovers, dandelion, common chickweed, perennial ryegrass, annual bluegrass and tall fescue. Katana efficacy on perennial ryegrass will aid in transition of overseeded bermudagrass in the spring and control ryegrass “clumps” in undesirable locations.

Celsius (68 WDG) is a new combination product for postemergence weed control with excellent activity on numerous broadleaf and grassy weeds. Thiencarbazone and iodosulfuron are two new active ingredients in turf while dicamba is an older chemistry used for broadleaf weed control. Celsius is labeled for use on residential lawns, golf courses, sports fields, parks, sod farms and other turf areas. Celsius may be applied from 2.5 to 7.4 oz of product per acre for use in bermudagrass, buffalograss, centipedegrass, St. Augustinegrass and zoysiagrass with activity on numerous annual and perennial broadleaf weeds. Celsius does not control mature crabgrass or annual bluegrass and should only be used on warm-season turfgrasses.

Patrick McCullough, Ph.D., is an extension turfgrass weed specialist at the University of Georgia.