Weed management options on golf course putting greens

Significant weed infestations are not common on creeping bentgrass and hybrid bermudagrass putting greens, but when they are, help is available.

J.T. Brosnan, Ph.D.; G.K. Breeden, M.S.; and A.J. Patton, Ph.D.

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Summer stress from heat, drought, and disease as well as mechanical injury from equipment and golfer traffic can compromise putting green quality and provide opportunity for weed invasion.
Photos by A. Patton

The two most common turfgrass species  planted on golf course putting greens are  creeping bentgrass (Agrostis stolonifera) and  hybrid bermudagrass (Cynodon dactylon × C.  transvaalensis). When managed appropriately,  both species provide high-quality playing  surfaces. However, turfgrasses managed for  putting green use are subjected to a considerable  amount of stress. These grasses are often  mowed daily at heights less than 0.15 inch (3.81  millimeters) and are subjected to heavy traffic  from both golfers and maintenance equipment.

Broadleaf and monocot (grasses, sedges,  kyllinga) weeds can invade putting greens  lacking density and vigor. Reduction in density  and vigor may come from mechanical injury  following cultivation and traffic, voids  left from ball marks, damage from insects and  disease, and environmental stresses, which  can all lead to weed invasion. Weed control  on golf course putting greens can be difficult  as few herbicides are labeled for use on putting  greens because stress renders them more  susceptible to herbicide injury that can compromise  both aesthetic and functional turf  quality. Additionally, putting green turf is the  most valuable acreage on the golf course and  is expensive to repair if injured. Many companies  do not register herbicides for use on  greens because they want to avoid being liable  for potential injury and because putting greens  make up an infinitesimally small percentage  of the total turf acreage in the world. In many  instances, herbicide labels neither allow nor  restrict applications to putting greens, which  places all liability on the end users.

Grassy weeds

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Smooth crabgrass growing in a creeping bentgrass putting green maintained at less than 0.150 inch.

Crabgrass (Digitaria species), goosegrass  (Eleusine indica) and annual bluegrass (Poa  annua) are three of the most common annual  grassy weeds of creeping bentgrass and hybrid  bermudagrass putting greens.

Crabgrass and goosegrass

Summer annual species such as crabgrass  and goosegrass germinate in spring, and seedlings  mature throughout the summer. Preemergence  control of these weed species is the  easiest means of control. A list of pre-emergence  herbicides labeled for creeping bentgrass and hybrid bermudagrass greens is presented  in Table 1. For each herbicide, check the label  to ensure the product is safe to use on the species  and cultivar grown. For example, older  creeping bentgrass varieties such as Cohansey,  Carmen, Seaside and Washington are more  susceptible to dithiopyr and siduron (Tupersan)  injury (6). It is also important to use only  labeled herbicides at labeled rates as off-label  applications can injure root systems and compromise  putting green quality.

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Goosegrass is a problematic summer annual in creeping bentgrass putting greens maintained in the transition zone and in bermudagrass putting greens maintained throughout the southern U.S.

Currently, no herbicides are labeled for  selective post-emergence control of crabgrass or goosegrass on creeping bentgrass putting  greens (Table 2). However, research trials  often indicate good control of one-tiller  or smaller crabgrass and goosegrass with  fenoxaprop (Acclaim Extra, Bayer) at 3.5 fluid  ounces/acre (256 milliliters/hectare) on creeping  bentgrass putting greens with no appreciable  injury. Furthermore, newly published  research shows that a pre-mixture of 2,4-D  + dicamba + MCPP + carfentrazone (Speed-  Zone) can control goosegrass without injuring  creeping bentgrass putting greens (12). Despite  these reports, these tools are not available to superintendents  since neither product is registered  for use on creeping bentgrass putting greens.

On hybrid bermudagrass putting greens,  diclofop (Illoxan, Bayer) and foramsulfuron  (for example, Revolver, Bayer) can be used for  post-emergence goosegrass control. However,  diclofop will no longer be available after December  2014 (Jeff Michel, Bayer Environmental  Science, personal communication). For  post-emergence crabgrass control on bermudagrass  greens, no effective options are available,  as herbicides such as trifloxysulfuron  (Monument, Syngenta) exhibit only marginal  activity against crabgrass species

Annual bluegrass

Annual bluegrass (Poa annua) is a winter  annual grassy weed common in creeping  bentgrass and hybrid bermudagrass putting  greens. Pre-emergence control of annual bluegrass  can be erratic because this weed is able  to germinate in a wide range of environments  (9,10). Post-emergence control is difficult not  only because of the limited number of labeled  herbicides, but also because of the possibility  of multiple annual bluegrass biotypes persisting  in putting greens, including both an annual-  type (P. annua cv. annua) and perennialtype  (P. annua cv. reptans).

Currently, no herbicides are labeled for  selective, post-emergence annual bluegrass  control in creeping bentgrass putting green  turf. However, sequential applications of plant  growth regulators such as paclobutrazol (for  example, Trimmit, Syngenta) and flurprimidol  (for example, Cutless, SePRO) often reduce  annual bluegrass populations in creeping  bentgrass putting greens and/or control seedhead  production (13). Although the products  are not labeled for use on putting greens, some  turfgrass managers have successfully reduced  annual bluegrass populations with the herbicides  Velocity SG (bispyribac-sodium, Valent)  and Xonerate (amicarbazone, Arysta Life-  Science) (8,13). Additionally, a great deal of  interest exists among golf course superintendents  in the experimental herbicide PoaCure  (methiozolin, Moghu), which can control annual  bluegrass in creeping bentgrass putting  greens. The future of this experimental herbicide  is still largely unknown at this time.

On hybrid bermudagrass greens, trifloxysulfuron  can be used for post-emergence annual  bluegrass control, along with foramsulfuron  (Revolver), pronamide (Kerb, Dow  AgroSciences), and rimsulfuron (for example,  TranXit, DuPont). Caution should be heeded  when attempting to control annual bluegrass  with sulfonylurea herbicides labeled for putting  greens (trifloxysulfuron, rimsulfuron) as  annual bluegrass populations resistant to these  herbicides were recently found in Alabama,  Georgia and South Carolina (5,11) and these  herbicides can move laterally and damage adjacent  cool-season turfgrasses.

Sedge and kyllinga species

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Creeping bentgrass roots were severely injured in this putting green following an off-label application of dithiopyr (Dimension 2EW) to a putting green. Roots were severely stunted and clubbed, and rooting depths were extremely shallow causing summer management problems/challenges on this putting green.

Sedge (Cyperus species) and kyllinga (Kyl-  linga species) species can invade both creeping  bentgrass and hybrid bermudagrass putting  greens. These species often invade poor-draining  or over-irrigated soils. Kyllinga species  tend to tolerate low putting green mowing  heights and greater mowing frequencies better  than sedges (4); therefore, kyllinga infestations  tend to be more prevalent in putting  greens. No herbicides are labeled for selective  control of either weed species on creeping  bentgrass putting greens although some have  successfully used spot treatments of halosulfuron  (for example, SedgeHammer, Gowan),  which is labeled for use on all areas of the  golf course except putting greens. On hybrid  bermudagrass putting greens, applications of  trifloxysulfuron provide kyllinga suppression  (Table 2).

Broadleaf weeds

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Annual bluegrass is a problematic weed because of its ability to produce viable seed under close mowing.

Although most broadleaf weeds cannot  survive at mowing heights used to maintain  putting greens, species such as white clover (Trifolium repens), mouse-ear chickweed (Cerastium  vulgatum), dandelion (Taraxacum  officinale), cudweed (Gnaphalium or Gamochaeta  species) and prostrate spurge (Euphorbia  humistrata) can persist even with the use  of sound management practices. Broadleaf  herbicides like 2,4-D have been used on putting  greens since the 1940s for weed control  (1,2), but many superintendents today are hesitant  to use broadleaf herbicides on their putting  greens for fear that turfgrass injury might  occur — especially from 2,4-D applications  in summer. Labels for many of the herbicides  listed in Table 2 neither allow nor restrict applications  to creeping bentgrass or hybrid bermudagrass  greens, leaving liability on the end  user in the event undesirable turfgrass injury  occurs after application.

Mixtures of synthetic auxin herbicides can  be used at reduced rates to control broadleaf  weeds on putting greens. For example, 2,4-D  + MCPP + dicamba (for example, Trimec  Classic, PBI/Gordon) can be applied to creeping  bentgrass putting greens at 1 fluid ounce  of formulated product per 1,500 square feet.  The label does caution against applications  when creeping bentgrass putting green turf  is under heat or drought stress and highlights  that injury after application will be shortlived.  A different formulation (for example,  Trimec Bentgrass Formula, PBI/Gordon) is  labeled for use on creeping bentgrass greens at  rates less than or equal to 1 fluid ounce of formulated  product per 1,000 square feet (3.18  milliliters/hectare). Trimec Bentgrass Formula  applies less 2,4-D (0.15 pound ae/acre  vs. 0.45 pound ae/acre (168 grams ae/hectare  vs. 504 grams ae/hectare) than Trimec Classic  when applied per label directions.

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White clover in a creeping bentgrass putting green.

Carfentrazone (for example, QuickSilver  T&O, FMC Corp.) is a post-emergence  broadleaf weed control herbicide labeled for  use on creeping bentgrass and hybrid bermudagrass  putting greens. Rates range from 1.0  to 2.0 fluid ounces/acre (73 to 146 milliliters/  hectare); however, the product can be used at  6.7 fluid ounces/acre (490 milliliters/hectare)  for managing silvery thread moss (Bryum argenteum).  Research in Tennessee indicates  Quicksilver applications combined with appropriate  cultural practices (for example, increased  nitrogen fertility and sand topdressing)  control silvery thread moss better than  simply spraying the herbicide alone (3).

Recent broadleaf research

There is very little data on the safety of  broadleaf herbicides on putting greens despite  pesticide labels that suggest that they can be  used without injuring turf. Research was conducted  at Purdue University and the University  of Tennessee during 2011-2012 to determine  the safety of post-emergence broadleaf  herbicides on putting green-height creeping  bentgrass turf.

An experiment was conducted twice at the  W.H. Daniel Turfgrass Research and Diagnostic  Center at Purdue University in West  Lafayette, Ind., and the East Tennessee Research  and Education Center in Knoxville,  Tenn., at the University of Tennessee. The  Indiana location was Pennlinks creeping bentgrass grown on a sand root zone built to  USGA recommendations and, in Tennessee,  the site was L-93 creeping bentgrass grown  on a silt loam soil frequently topdressed with  a USGA-recommended sand. The locations  were maintained as putting greens. Plots were  treated with herbicide on Oct. 24, 2011, and  an adjacent location on May 22, 2012, in Indiana  and on Oct. 17, 2011, and an adjacent location  on May 1, 2012, in Tennessee. At both  locations, herbicides were applied in 2 gallons  water/1,000 square feet at 30 psi (81.5 milliliters/  square meter at 207 kilopascals) with a  CO2-pressurized boom sprayer equipped with  an XR8002VS flat-fan nozzle.

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Table 3.
Injury ratings following applications of broadleaf herbicides to creeping bentgrass putting greens in the fall or the spring in Indiana and Tennessee at label rates and twice (2×) the label application rates.

Herbicides included in this study (Table  3) were all labeled for use on creeping bentgrass  putting greens and applied at the putting  green label rate and at a rate twice (2×)  this labeled rate. One exception to this was the  October 2011 application timing in Tennessee  where only the label rate of each herbicide was  applied. An untreated check was included for  comparison at each location. Injury to creeping  bentgrass and turf quality data were collected.  All data were analyzed using statistical  software.

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Mouse-ear chickweed is a common weed in close-mowed bentgrasses.

Fall applications. Minor and transient injury  was observed from fall treatments on  creeping bentgrass putting greens in Indiana,  but injury levels were acceptable (≥ 7,  on a scale of 9-1, where 9 = no injury) for all  treatments including herbicides applied at a  2× rate (Table 3). Minor but acceptable injury  occurred from applications of 4-Speed,  4-Speed XT, Banvel, Trimec Bentgrass,  Trimec Classic, Trimec Encore and Trimec  Southern. In Tennessee, injury was minimal  (<4%, on a scale of 0%-100%, where 0% =  no injury) and transient from labeled application  rates following 4-Speed, 4-Speed XT,  Trimec Classic, and Trimec Southern applications.  Differences in turf quality were not  seen among treatments in Indiana or Tennessee  (data not shown).

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Silvery-thread moss is a common putting green weed, especially in close-mowed putting greens that receive frequent irrigation and low fertility.

Spring applications. The experiments were  repeated in May 2012 to determine if more injury  might be expected from late spring and  summer applications during warmer temperatures.  At both locations, more injury was  observed from May 2012 applications than  October 2011 applications. Applications at  label rates did not cause unacceptable injury  when applied in Indiana in May, but 2× rates  of 4-Speed XT, Banvel and Trimec Southern  did cause unacceptable injury two weeks after  application (Table 3). That injury was acceptable  by three weeks after application (data not  shown). Results were similar in Tennessee  with 4-Speed XT, Banvel and Trimec Southern  applied at the 2× rate also causing the most  injury (11%-19%) (Table 2), but with injury  decreasing to <4% three weeks after application  (data not shown). While a labeled application  rate of Banvel caused 10% injury two  weeks after application in Tennessee, other  products such as Mecomec 2.5, QuickSilver  T&O, Trimec Bentgrass, Trimec Classic and  Trimec Encore had <2% injury when applied  at the labeled rate in May, similar to responses  observed in Indiana. These data are supported  by reports on the safe use of carfentrazone  on creeping bentgrass for silvery thread moss  (Bryum argenteum) control (15) and the use of  Trimec Bentgrass for lesser swinecress (Croronopus  didymus) control (14).

Findings of this research were that broadleaf  herbicides labeled for putting green use  can be safely applied at labeled rates in the  spring and fall; injury is more likely to occur  from May herbicide applications than from  October applications; some herbicides are safer than others with high rates of dicamba,  triclopyr and 2,4-D causing injury; and unacceptable  injury can occur from higherthan-  labeled herbicide rates such as from spot  applications.

Conclusions

Although most golf course superintendents  have few weed problems other than annual  bluegrass in their putting greens, weeds  do occasionally invade. If only a handful of  weeds are present within a single green, mechanically  removing these weeds is the most  efficient method of control. Herbicide applications  are only warranted when weed pressure  is significant. In these cases, research has  confirmed that several herbicides labeled for  use on putting greens can be used safely and  successfully to control weeds when label directions  are followed.

More herbicides are registered for use on  fairways and tees than on putting greens.  Considering the scope of efficacy and tolerance  testing required across a wide geographic  region before a herbicide receives labeling,  there is likely good reason a particular product  is not labeled for putting green use — it could  result in undesirable injury. Herbicide labels  that neither restrict nor allow putting green  use place all liability on the end user, so use  caution with these products. For these reasons,  it is best to use only products with specific label  instructions for putting greens.

Acknowledgments

The authors would like to thank Drs.  Lambert McCarty and Travis Gannon for  their assistance with this manuscript.

This article is a compilation of previously  published University of Tennessee and Purdue  University Extension publications and a  research article authored by the same authors  in Applied Turfgrass Science.

  • Brosnan, J.T., and G.K. Breeden. 2011.  Herbicides for Use on Golf Course Putting  Greens. University of Tennessee Extension  Publication W268. Knoxville, Tenn.
  • Patton, A.J., and D.V. Weisenberger. 2014.  Turfgrass Weed Control for Professionals.  AY-336. Purdue University Extension Publication,  West Lafayette, Ind.
  • Patton, A.J., D.V. Weisenberger, J.T. Brosnan  and G.K. Breeden. 2013. Safety of labeled  herbicides for broadleaf weed control  in creeping bentgrass putting greens. Applied  Turfgrass Science doi:10.1094/ATS-  2013-0523-01-BR.

Literature cited

  1. 1.Anonymous. 1946. Fall care of bentgrass putting  greens. Timely Turf Topics. USGA Green Section  Record October/November. p. 1.
  2. Bingham, S.W. 1969. Herbicides and putting green  turfgrasses. Proceedings International Turfgrass  Research Conference 1:374-379.
  3. Borst, S.M., J.S. McElroy and G.K. Breeden. 2010.  Silvery thread moss control in creeping bentgrass  putting greens with mancozeb plus copper hydroxide  and carfentrazone applied in conjunction with cultural  practices. HortTechnology 20:574-578.
  4. Busey, P. 2003. Cultural management of weeds: a  review. Crop Science 1899-1911.
  5. Cross, R., L.B. McCarty, N. Tharayil et al. 2013.  Detecting annual bluegrass resistance to ALSinhibiting  herbicides using a rapid diagnostic assay.  Weed Science 61:384–389. doi:10.1614/WS-D-12-  00172.1
  6. Dernoeden, P. 2013. Creeping Bentgrass Management.  CRC Press, Boca Raton, Fla.
  7. Haguewood, J.B., and X. Xiong. 2012. Control of  crabgrass on creeping bentgrass (Agrostis stolonifera  L.) putting greens using preemergence herbicide. Proceedings  North Central Weed Science Society 67:39.
  8. Jeffries, M.D., F.H. Yelverton and T.W. Gannon 2013.  Annual bluegrass control in creeping bentgrass putting  greens with amicarbazone and paclobutrazol.  Weed Technology 27:520-526.
  9. Kaminski, J.E., and P.H. Dernoeden. 2007. Seasonal  Poa annua L. emergence patterns in Maryland. Crop  Science 47:775-781
  10. McElroy, S. 2012. Herbicide-resistant weeds: A  21st century problem. Golf Course Management  80(11):84-86, 88.
  11. McElroy, J.S., R.H. Walker, G.R. Wehtje and E. van  Santen. 2004 Annual bluegrass (Poa annua) populations  exhibit variation in germination response to temperature,  photoperiod, and fenarimol. Weed Science  52:47-52.
  12. Reicher, Z. 2014. Controlling moss or goosegrass in  new creeping bentgrass seedlings. Online. http://turf.  unl.edu/pdfctarticles/June9_CBG_Seedlings_moss_  goosegrass.pdf
  13. Reicher, Z., M. Sousek, R. Calhoun et al. 2013.  Controlling Poa annua on putting green height turf  in Indiana, Michigan, and Nebraska: 2012 Research  Update. 2012 Annual Report–Purdue University Turfgrass  Science Program, p. 32-34. Online. www.agry.  purdue.edu/turf/report/2012/PDF/2012_Purdue  TurfResearchSummary.pdf
  14. Straw, C., G. Henry, T. Williams et al. 2012. Postemergence  control of lesser swinecress in creeping  bentgrass putting greens. ASA, CSSA, and SSSA  Annual Meetings, Cincinnati, Ohio. Oct. 21-24, 2012.  Paper 105-7.
  15. Thompson, C., J. Fry and M. Kennelly. 2011. Evaluation  of conventional and alternative products for  silvery-thread moss control in creeping bentgrass.  Online. Applied Turfgrass Science doi:10.1094/ATS-  2011-1018-01-RS

Jim Brosnan (Twitter: @UTTurf  weeds) is an associate professor of turfgrass weed science  and Greg Breeden is an Extension specialist at the  University of Tennessee, Knoxville, Tenn. Aaron Patton is  an associate professor at Purdue University, West Lafayette,  Ind.