SmutgrassManagementinBermudagrassandBahiagrassPastures

Smutgrass(Sporobolusindicus)isatuftformingnon-native perennial weed that affects manyimproved perennial grass pastures in Texas,Florida,Georgiaandothersouthernstates.Asawarm season perennial, smutgrass remainsdormant in the winter, begins growing in thespring, and can produce seed from July toSeptember. InFlorida,smutgrass isconsideredthe third most troublesome weed in pastures(Crawford2007)likelyduetoitsabilitytoadaptto almost all soil types and to its competitivenature in pastures. While some grazing ofsmaller more tender smutgrass may occur,cattle will not preferentially consume maturesmutgrasspossiblyduetoareductioninforagequality as the grass matures (McCaleb et al.1963; Smith and Cole 1972; Mullahey 2000).Therefore, if left untreated, smutgrasspopulations can dominate grazing lands toexclusion of the desirable species (Simon andJacobs1999).

Control of smutgrass throughmowing, fertilitymanagement, and intensive rotational grazinghas traditionally been difficult to achieve.Whileithasbeenshownthatsmutgrassgrowthwill decline with intense grazing management

(Ahmad1979),maintainingtheneededlevelofgrazing pressure without overgrazing desirablespeciescanbeverychallenging.

Moreconsistentmanagementofsmutgrasshasbeen achieved through use of herbicides, andfrom the 1950’s through the 1980’s the onlyselective herbicide availablewas Dalapon (2,2-Dichloropropionic acid). In the late 1980’s anew product called Velpar (hexazinone) waslabeled for use in established stands ofbermudagrassandbahiagrassforthecontrolofsmutgrass.Currently,Velpar®LVUismarketedandsoldbyBayerandistheprimarychemistryrecommendation for the control of smutgrassacross the southern US. Research has shownVelpartoprovidegoodcontrolwhenappliedinlate spring/early summer to actively growingsmutgrass,whenrainfallistypicallysufficienttomove the herbicide into the root zone foruptake. More consistent long-term control istypicallyachievedwhenasequentialapplicationis made in the following year (Mislevy et al.1999; Rana et al. 2015). Current pricing forVelpar would typically be around $40/acdepending on the rate utilized. Based onresearch conducted by B. J. Brecke (1981),

SCS-2017-18

ScottNolte,Professor & StateExtensionWeedSpecialistTexasA&MAgriLifeExtensionService,TexasA&MUniversity

hexazinone the active ingredient in Velpar,providedslightlybettercontrolof smutgrass inbahiagrass pastures and with lowerphytotoxicity.WhenapplyingVelpar,caremustbe taken to maintain a buffer of 100 feetbetween the area of application and anydesirabletreesordeathofthetreemayoccur.Application rates are 2¾ to 4½ pints per acre.Usethelowerrateonsandysoilsandthehigherrate on heavier textured clay soils. Livestockmay be grazed immediately following abroadcastapplicationofVelpar®LVUHerbicideatratesof4.5pintsperacreorless,andtreatedvegetationmaybe cut, dried, and fed after 38days.

Anon-selectiveherbicideoptionwouldbeusingglyphosate (Roundup) in a rope-wick, rotarywiperorspottreatmentmethod.Forrope-wickorrotarywiperapplications,therecommendedmixture isa1:2 (1galofglyphosate in2galofwater) rateduringactiveweedgrowthand forperennials, at seedhead formation. Livestockmustberemovedafterapplicationanda14daywait before grazing and harvesting. No morethanone-tenthofanyacreshouldbetreatedata time. For spot treatments, a 1.5 to 2.0%solutionofa4.5lb/gallonglyphosateproductisrecommended (2.0 to 2.5 fl oz per gallon ofwater). Livestockorhayharvest can return tospot-treatedpastures7daysafterapplication.

ReferencesAhmad,I.B.1979.Effectsofnitrogenandgrazingon

asmutgrass–bahiagrass–whitecloverpasture.Master’sthesis.Gainesville,FL:UniversityofFlorida.93p.

Brecke,B.J.1981.Smutgrass(Sporoboluspoiretii)controlinbahiagrass(Paspalumnotatum)pastures.WeedSci.29:553–555.

Crawford,S.C.andL.F.Wiggins.2007.BeefForageRangePracticesinSouthFlorida.UniversityofFloridaInstituteofFoodandAgriculturalSciencesCooperativeExtensionService.6P.

McCaleb,J.E.,E.M.Hodges,andW.G.Kirk.1963.Smutgrasscontrol.FloridaAgriculturalExperimentStation,Ona.CircularS-149.10p.

Mislevy,P.,D.G.Shilling,F.G.Martin,andS.L.Hatch.1999.Smutgrass(Sporobolusindicus)controlinbahiagrass(Paspalumnotatum)pastures.WeedTechnology.13:571–575.

Mullahey,J.J.2000.Evaluatinggrazingmanagementsystemstocontrolgiantsmutgrass(Sporobolusindicusvar.pyramidalis).Pages59–60inProceedingsofthe53rdSouthernWeedScienceSociety,Tulsa,OK:SouthernWeedScienceSociety.

Rana,N.,B.A.Sellers,J.A.Ferrell,G.E.MacDonald,M.L.Silveira,andJ.M.Verdramini.2015.Integratedmanagementtechniquesforlong-termcontrolofgiantsmutgrass(Sporobolusindicusvar.pyramidalis)inbahiagrasspastureinFlorida.WeedTechnology.29:570-577.

Simon,B.K.andS.W.L.Jacobs.1999.RevisionofthegenusSporobolus(Poaceae,Chloridoideae)inAustralia.Aust.Syst.Bot.12:375–448.

Smith,J.E.andA.W.Cole.1972.Selectivecontrolofsmutgrassinpermanentpastures.Page194inproceedingsofthe25thSouthernWeedScienceSociety:SouthernWeedScienceSociety.

ProducedbytheDepartmentofSoilandCropSciences

soilcrop.tamu.edu

Theinformationgivenhereinisforeducationalpurposesonly.Referencetocommercialproductsortradenamesismadewiththe

understandingthatnodiscriminationisintendedandnoendorsementbytheTexasA&MAgriLifeExtensionServiceisimplied.

TexasA&MAgriLifeExtensionisanEqualopportunityemployerandprogramprovider.

TheTexasA&MUniversitySystem,U.S.DepartmentofAgriculture,andtheCountyCommissionersCourtsofTexasCooperating.