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Research You Can Use

FieldTesting Plant GrowthRegulators and Wetting Agents forAnnual Bluegrass Seedhead SuppressionResearchers use Chicago-area golf courses to exploresuppressing annual bluegrass flowering.BY RANDY KANE AND LEE MILLER

Left:Research supported by the Chicago District Golf Associationtested the ability of plant growth regulators and wetting agents tosuppress annual bluegrass seed head formation.Above: Heavy Poaannua seedhead formation on Midwest putting greens is typical inmid to late May in most years.

Many of the annual bluegrassbiotypes inhabiting the golfcourses of Illinois have a winter

annual life cycle. That is, these biotypesgerminate from seed in auturrm, over-winter in a vegetative state, flower andset seed in the spring, and then declineor completely die out during the heatof summer.

Where annual bluegrass is a signifi-cant component in a turf, profuse seed-ing may occur in late April throughMay and can become objectionable forseveral reasons. First, profuse seedingcan turn an annual bluegrass-contami-nated green or fairway almost white incolor, prompting questions about grasshealth. Second, putting greens with

significant annual bluegrass populationsprovide very poor putting surfacesduring spring flowering. Seedheadsadversely affect ball roll, causing greensto become slower and more bumpy.Third, heavy seeding of annual blue-grass contributes to the seedbank insurface soil and thatch layers, thus pro-moting the long-term survival andspread of the species.

There is a growing body of evidencethat suggests heavy seeding may not bebeneficial for the near-term survival offlowering annual bluegrass. Seed pro-duction may divert photosynthate awayfrom vegetative tissues Oeaves and roots)to the flowers, resulting in reduced rootdepth and shoot growth after seeding.

Annual bluegrass that hasn't set seed(e.g., in treated plots) is usually betterable to survive summer stresses thanplants that have flowered and set seed(2). It is interesting to note that most ofthe plants identified as perennial biotypesof annual bluegrass produce less seedthan annual biotypes, which may con-tribute to their longer-term, perennialhabit.

Chemical seedhead suppression canhelp maintain the color and playabilityof fairways, as well as the speed andtrueness of putting greens. Also, manysuperintendents feel that by reducingseed set and the annual contributionsto the seedbank, other chemical andmanagement programs used to reduce

JULY-AUGUST 2003 21

Embark Turf & Ornamental can cause discoloration and thinning of creeping bentgrass mowed atgreens height-of-cut (below pen).

or eliminate annual bluegrass fromcool-season turf may become moreeffective.There also is a great deal ofinterest in trying to preserve the purityof newly renovated turf by keepingnearby annual bluegrass from contami-nating the renovated site (e.g., a resur-faced putting green).

TECHNIQUESTO INHIBITANNUAL BLUEGRASSFLOWERINGHow do you reduce or suppress annualbluegrass seed set in the spring? Severalherbicides and plant growth regulatorsare known to inhibit seeding of Foaspecies and other grasses,includingolder products like maleic hydrazide,mefluidide, and endothal (Table 1).However, most products used in annualbluegrass programs have problems withconsistency of seedhead suppression,length of time seedheads are suppressed,or phytotoxicity. Also,application timingand proper stage of plant growth arecritical for best seed inhibition, andcalendar dates for application may varywidely from year to year. Note thatthere is a "base-50" growing-degree-dayprediction model for timing of the firstspray for seedhead suppression (3),butthis model seems to be as unpredictableas the annual bluegrass itself (Table 2).

Historically, the best results forseedhead suppression on annual blue-grass fairways have been found usingmefluidide ("Embark") (1,5). However,timing and phytotoxicity problems havelimited its use, especially on greens-height turf. Many superintendents havetried early spring applications ofgibberellin inhibitor plant growth regu-lators (PGRs) such as paclobutrazole("Trimmit") or flurprimidol ("Cut-less") to try to slow the encroachmentof annual bluegrass into bentgrass turf.They reported some seedhead suppres-sion following early season treatments,but seedhead suppression usually is notthe primary goal of these applications.

A few adventurous superintendentshave also used the wetting agent Aqua-Gro L (5) to limit spring flowering of

22 G R E ENS E C TI 0 N R E COR D

annual bluegrass, and they have foundthat Aqua-Gro is lessphytotoxic thanEmbark, but it provides more variableresults. (Aqua-Gro L is no longermanufactured. )

Preliminary field tests have suggestedthe ethephon ("Proxy") has goodactivity for annual bluegrass seedheadsuppression (4).Proxy is a new PGRfor the turf market, but it has beenavailablein agricultural applications foryears.Proxy may be safer and havemore timing flexibility than Embark,and it could be a potential substitute forAqua-Gro L. Proxy reportedly has thetendency to make treated turf lightergreen to yellow-green, but this can becounteracted to some extent with ironapplications.Also, tank-mixes of Proxyplus trinexepac-ethyl (primo) haveshown good results with less turfdiscoloration.

PRODUCTS TESTED ANDAPPLICATION TECHNIQUESThree golf course sites were treatedwith PGRs and wetting agents in Apriland May of 2000-02, including bothgreens- and fairway-height turf. Initialtreatments were timed to coincide withflowering of the earliest annual blue-grassbiotypes. Individual plots were 40-50 sq. ft. in size and were replicated twoor three times, depending on spaceavailable.Treatments were applied witha CO2-powered backpack sprayer (35psi, flat fan nozzles).

Proxy was tested alone and in tankmixes with Primo and Trimmit. Singleand multiple applications of Proxy weremade at 5-7.5 fl. oz. per 1,000 sq. ft.rates. Primo was applied alone and intank mixes at 5-10 fl. oz. per acre.Trimmit was applied at rates rangingfrom 6-8 fl. oz. per acre.Aqua-Gro L

has been tested for a number of yearson putting greens at 8 fl. oz. per 1,000sq. ft., usually with follow-up applica-tions at 4-8 fl. oz. per 1,000 sq. ft. oneweek later.

The wetting agent Cascade was alsoincluded in the study to see if a differenttype of wetting agent chemistry couldinhibit seedheads (note that the manu-facturer makes no claims of seedheadcontrol). Embark (Turf & OrnamentalGrowth Regulator formulation) at 1.3fl. oz. per 1,000 sq. ft. was included as astandard, and to test for phytosafety ongreens-height turf

SUMMARY OF RESULTSFROM EARLY STUDIESA general overview of field test datafrom Chicago area trials in 2000-01 ongreens-height turf can be found inTable 3. Note that the percent seedhead

J U L Y - AU GUS T 2003 23

90Figure I

Proxy tank mixes for Poa annua seedhead suppression on fairway-height turf

May 10,2002

• Check • Proxy (5 oz.) alone

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May 31,2002

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inhibition is an average of several tests,and results can vary greatly withweather conditions, application timing,and annual bluegrass biotypes present intreated areas. Embark is consistently thebest flower suppressor, but phytotoxicity(primarily on creeping bentgrass) re-mains a major concern in northernIllinois. Phytotoxicity of Embark treat-ments was expressed as a dark blue-green to brown color, with some thin-ning of the stand. Once warmerweather arrived, turf color and densityrecovered.

Proxy and Proxy + Primo treat-ments provided seedhead suppressionapproaching that of Embark in ourtrials in 2000 and 2001. In some cases,suppression with split applications of

24 GREEN SECTION RECORD

Proxy lasted longer than single Embarkapplications. However, higher rates orrepeat applications of Proxy causedyellowing and thinning of treated turf,especially at greens height. Note thatrepeat Proxy applications were madeonly 7 to 10 days apart; less discolorationhas been observed in other tests if theinterval between applications is 28-35days (4).Tank mixing Proxy with Primoappeared to reduce the discolorationand thinning of turf, although furthertesting will be required to confirm theeffect.

Of the other products/rates tested,only Aqua-Gro L exhibited significantseedhead suppression, and the effect wasshort-lived and inconsistent from site tosite and season to season. The anti-gib-

berellin growth regulators Primo andTrimmit did not appear to inhibit seed-head formation, and in some situations,these treatments appeared to have moreseedheads than check plots. This effectcould be due to stunting of the seedstalk to the point where the seedheadsremained below the cutting height andwere not removed by mowing.

OBSERVATIONS FROM2002 STUDIESFor 2002 greens-height trials, we con-centrated on Proxy alone or in tankmixes with Primo or Trimmit (Table 4).We also began a second set of treat-ments a week later to see if a laterapplication was as effective as a well-targeted first application. The Proxy and

bluegrass/creeping bentgrass fairway(Table 5 and Figure 1).Taking theProxy rate up to 7.5 fl. oz. per 1,000 sq.ft. improved the seedhead suppression,and no noticeable phytotoxicity wasobserved at this rate when tank mixedwith Primo at 10 fl. oz. per acre. Proxydoes not have a separate label rate forfairway treatments or a recommendedrate for putting greens on the 2002pesticide label. It is likely that somebroader uses and application rates willappear on future labels.

CONCLUSIONS AFTERTHREEYEARS OFTESTINGAfter three years of testing products forannual bluegrass seedhead suppression,some conclusions can be reached.

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Proxy+ tank mixes did not perform aswell as in the previous two years. Oncertain rating dates, the level of seed-head suppression was hovering around50 percent, with the best levels around70% suppression. Previous tests providedabout 90% suppression.Variability inseedhead suppression with PGRs iscommon (3, 5) and may be due to dif-fering weather and application timingparameters, as well as to the inherentvariability of annual bluegrass biotypes.Proxy treatments applied a week laterthan the supposed target date still per-formed well once the time lag wastaken into account.

Finally, we took a look at some Proxytank mixes sprayed on a mixed annual

Shade patternsinfluencePoa annuagrowth andits competitionwith bentgrass.

• Seedhead production in annual blue-grass is detrimental for various reasons,including poor playability, aesthetics,and reduced plant vigor.• The most consistent seedheadsuppression follows treatments withmefluidide or ethephon, although bothchemicals have limitations regardingapplication timing or possiblephytotoxicity.• Embark can cause discoloration andthinning of bent grass following coldweather, but it remains the best productfor seedhead suppression, especially on

, Table 5 ,Percent annual bluegrass seedhead ~uppression on fairway; turf,-: 2002*

, ~,!' .• , % $eed~,ead Suppressie>p:,* "Rate~r . "': . ''''... I"

) ,000 sq. ft. "MayJO May 24 " May 31'" '1M I '

rrfuPOO~ p, ' 5 fl.&<?~~~~! ':~+" ."" ,"HI

Pro,- : Pnmo;. 5 + .25fLoz. 75

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proxy +Trimmit 5 + .28 fl. ~z. 3~, *Application tlate for all treatments was Ap~k2.~; 2002 .. "

I ." ullitr " .' '. ,\~I ~~; l>j, ',w . ". 'f II'::"**Oatashow percent~uction in's~heads,.corrtpareCI to,untteat~d plots.

J U L Y - A U GUS T 2003 25

Visible seedheads were evident inuntreated plots when comparedto surrounding treatments that

demonstrated varying abilities tosuppress seedheads.

Higher rates of Proxy (withoutPrimo or chelated iron) causedsome discoloration of treated turfmow"edat putting green height.Patchy seedhead development isevident in the check plot at left.

fairways, where some phytotoxicity istolerable.• Proxy can be nearly as effective asEmbark for seedhead suppression, butresults are variable from year to year andfrom site to site.

• Proxy can cause some objectionablecolor and growth effects, but tank mixeswith Primo or other PGRs may allevi-ate some of these problems.• If Proxy (+Primo) applications aremade early in spring, a follow-up appli-cation 4-5 weeks after the first may bebeneficial to maintain the seedheadsuppression into June.• Wetting agents gave inconsistentresults and were approximately 50% aseffective as mefluidide or ethephon,at best.• Anti-gibberellin PGRs such aspaclobutrazole and trinexepac-ethyl didnot significantly reduce seedheads inour studies.

26 GREEN SECTION RECORD

• Seedhead suppression can be highlyvariable from year to year or site to sitebecause of weather fluctuations, appli-cation timing, and annual bluegrassvariability.

ACKNOWLEDGEMENTSThanks to our on-site cooperatorsand supporters for these studies:John Gurke, Superintendent, AuroraC.C.; Dan Anderson, former Super-intendent, FoxValley C.C.;Jim McNair,Superintendent, OrchardValley G.C.;Jon Jennings, Superintendent, ChicagoG.C.; Bruce Branham, Ph.D., AssociateProfessor, University of Illinois, Depart-ment of Natural Resources and Envi-ronmental Sciences; Paul Vermeulen,Director, Mid-Continent Region,USGA Green Section .

REFERENCES1. Cooper, R.]., P. R. Henderlong,J. R. Street,

and K.J. Karnok. 1987.Root growth, seedhead

production, and quality of annual bluegrass asaffected by mefluidide and a wetting agent.Agron.J,79(5):929-934.

2. Cooper, R.J., P. R. Henderlong, andJ. R.Street. 1984.Annual bluegrass management:getting to the root of the problem. Golf CourseManagement, 52(3):39-43.

3. Danneberger, T. K., B. E. Branham, and J. M.Vargas,Jr. 1987.Mefluidide applications forannual bluegrass seedhead suppression basedon degree-day accumulation. Agron. J,79(1):69-71.

4. Gelertner,W, and L.J. Stowell. 2001. Advancesin Poa seedhead management. Golf CourseManagement, 69(10):49-53.

5. Petrovic, A. M., R. H.White, and M.Kligerman. 1985.Annual bluegrass growth andquality as influenced by treatments of growthretardants and wetting agents. Agron.J,77(5):670-674.

DR. RANDy KANE is director of TuifgrassPrograms and Lee Miller is manager ofTuifgrass Research for the Chicago DistrictGolf Association.