Kill off bermudagrass with one less spraying - GCSAA

GCM - May 2000 - Research - Kill off bermudagrass with one less sprayingR E S E A R C HKill off bermudagrasswith one less sprayingReplacing obsolete turf requires freedom from old bermudagrass.John Boyd, Ph.D.KEY POINTS■ Tank mixing Fusilade II withRoundup Pro will reduce thenumber of applicationsneeded for completebermudagrass control.■ Tank mixing a burn-down herbicidesuch as Finale or Rewardwith a systemic herbicide suchas Roundup will reduce controlof perennial weeds.■ Repeat herbicide applicationsat moderate rates provide bettercontrol of tough perennialsthan a single application atthe maximum rate.68 Golf Course Management ■ May 2000Weed experts often warn golf coursesuperintendents in warmer climatesto control bermudagrass (Cynodonspecies) turf completely before replacingit. A proven program is three applicationsof glyphosate (Roundup Pro)during the current growing season, followedby spot spraying the followingspring to clean up the inevitable 1 to 2percent of missed bermudagrass.Unfortunately, turfgrass managersrarely feel they have the luxury of settingaside an entire growing season for preplantweed control. Most regret it later.What usually happensTypically, when a transition-zone golfcourse converts bermudagrass fairwaysto zoysiagrass (Zoysia japonica), thesuperintendent is under pressure tocomplete the job as soon as possible.Sprayers dispense four to five quarts ofglyphosate per acre, then crews planttwo to four weeks later with no additionalattempts at bermudagrass control.A follow-up treatment might beapplied seven to 10 days after the firstspraying to cover missed areas — sometimeseven though no regrowth isvisible yet. These treatments are oflittle value because glyphosate only killsgrowing plants.It is possible to get lucky and be suc-cessful with such an abbreviated program,but the odds are against it. One ortwo applications of glyphosate will notcontrol bermudagrass.The severity of future bermudagrassencroachment following incompletecontrol will vary from site to site.Bermudagrass is slower to appear onareas planted with sod compared withthose established from sprigs or seeds.Big-roll sod may further hinder thereappearance of an unwanted bermudagrassbecause there are fewer gaps thatbermudagrass can emerge through thanwith smaller rolls.Problems might not show up untilstress weakens the desirable turfgrass.Bermudagrass will readily invade thinspots. One of the first places we see bermudagrassappear is in areas of zoysiagrassor tall fescue (Festuca arundinacea)that have been weakened by brown patch(Rhizoctonia solani). Traffic, drought andother stresses also may open the door forbermudagrass encroachment.Bermudagrass to bermudagrassWhen converting a commonbermudagrass golf course to hybridbermudagrass, complete eradication ofthe undesirable bermudagrass is imperative.No herbicide can selectivelyremove one bermudagrass from

R E S E A R C HPhotos courtesy of John BoydJust two applications (top) of a mixture of Roundup Pro with Fusilade II were as effective atkilling bermudagrass as three applications of straight Roundup Pro (bottom).another. After establishment, all thatworks is mechanical removal and spotspraying with nonselective herbicides.Contamination from off the siteWhen buying sprigs or sod inbermudagrass country, inspect the farm.That is the best way to be reasonably surethat hybrid bermudagrasses are not contaminatedby off-types and that otherturfgrasses are free of bermudagrass.The best time to search a zoysiagrassfield for bermudagrass contaminationis in the early morning when bermudagrasspatches are very obvious becausetheir leaves retain dew more readilythan zoysiagrass leaves do.Sod farmsManaging bermudagrass invasion isGolf Course Management ■ May 2000 69

R E S E A R C Hmore difficult on sod farms than on golfcourses. Sod harvest creates an idealopening for bermudagrass encroachment.The rapid regrowth of bermudagrassgives it an advantage against lessaggressivespecies and allows it tospread before the desired grass coversthe open area. Many growers of zoysiagrassand centipedegrass have eliminatedbermudagrass production fromtheir farms to reduce the potentialfor contamination.A common sight on sod farms,where pre-plant bermudagrass controlfailed, is a skirmish line of workersadvancing across a field armed withbackpack sprayers. They are spot sprayingbermudagrass with glyphosate. Thedifficulty in achieving complete coverageand consistent follow-up applicationsunder these conditions makes thisa less-than-perfect method. Spot controlof bermudagrass is a job that rarelyends until the field is taken out of productionand cleaned up.Current recommendationsIn 1988, B.J. Johnson published thedefinitive research on preplantbermudagrass control. At Griffin, Ga.,Johnson demonstrated that three applicationsof Roundup Pro over a growingseason (May, June, August) wererequired for acceptable control ofbermudagrass.After countless calls from golf coursesuperintendents and sod farmers, wesought enhancements to this approach.Generally following Johnson’s methods,we combined some grass-specific herbicideswith glyphosate. Fusilade II (fluazifop-P-butyl)and Envoy (clethodim)Bermudagrass control9696■ 1 application■ 2 applications■ 3 applications70664615221712Various mixtures of Roundup with other herbicides provide very different results in the control of bermudagrass.70 Golf Course Management ■ May 2000

were selected based on past performancein bermudagrass controlstudies. We also included the nonselectiveherbicide Finale (glufosinate). Repeatapplications of the grass-specific herbicidesalone were not included because thebroadleaf and sedge control provided byRoundup is usually an important part ofturfgrass renovation programs.We initiated trials in May 1998 atsites about 50 miles apart in centralArkansas. One study was in a Tifwayhybrid bermudagrass field on a sodfarm. The other site used establishedplots of Tifway and Midlawn hybridbermudagrass located at the Universityof Arkansas research station at Lonoke.The herbicide treatments at eachlocation were identical, but theapplication timings varied slightlybecause the research station plotsreceived irrigation, whereas the sod farmplots relied solely on rainfall. Follow-upherbicide applications were not madeuntil regrowth appeared.At the sod farm, applicationsoccurred a few days after significant rainfallsto coincide with favorable growingconditions. The trial was repeated in1999 on Tifway at the sod farm.The experimental design was a randomizedblock design. Plots were 6 feetby 10 feet with four replications.Herbicides were applied with a carbondioxide pressurized backpack sprayer.The carrier volume was 20 gallons peracre. Application dates at Lonoke in1998 were May, July and September. In1998, the spray dates at the sod farmwere May, July and October. Applicationtimings on the sod farm site in 1999were May, June and September.ResultsResults were straightforward andeasy to interpret. Only two treatmentsprovided acceptable control:• The standard recommendation ofthree applications of Roundup Pro at2 quarts of product per acre• Two applications of a herbicide combination:2 quarts of Roundup Proplus 24 fluid ounces Fusilade II productper acreThe results from these two treatmentswere consistent across the threetrials at one year after treatment.Compared with Roundup Pro alone,the tank mix with Fusilade II allowsturfgrass managers to achieve the samelevel of control with two applicationsrather than three.Glufosinate, a contact herbicide,mixed with glyphosate severely reducedbermudagrass control during bothyears across all locations. Apparently,the rapid tissue destruction caused byglufosinate prevented translocation ofRoundup Pro within the plant, thereforereducing long-term control.Overall, herbicides applied in 1999were less effective than the same treatmentsapplied in 1998. The most logicalexplanation for the drop in control wasthe hot, dry conditions that persistedduring the summer of 1999.Our results support two basic tenetsof perennial weed control:• Tank mixing a fast-acting herbicidesuch as glufosinate with a slow-actingsystemic herbicide such as glyphosatewill reduce overall control. Threeapplications of Roundup Pro andFinale produced less than 50 percentcontrol in 1998 and 1999.• Repeat applications over time withpostemergence, systemic herbicidesare superior to a single applicationusing the maximum label rate of theherbicide. We included a glyphosatetreatment at 10 quarts per acre in our1999 trials. Five months after spraying,a single 10-quart application wasproviding zero control compared with98 percent control for three applicationsat 2 quarts per acre.■References1. Johnson, B.J. 1988. Glyphosate and SC-0224for bermudagrass (Cynodon) cultivar control.Weed Technology 2:20-23.John Boyd, Ph.D., is a weed scientist with Universityof Arkansas division of agriculture’s CooperativeExtension Service.Golf Course Management ■ May 2000 71R E S E A R C H