A historical perspective ofannual bluegrass control

Fighting Paa annua has kept researchersand superintendentsgainfully employed through more than eight decades.

Nick Christians, Ph.D.

It's not a joke anymore: Annual bluegrass can invade artificial turf.

Over the past 85 years, annualbluegrass has endured andthrived on golf courses

despite one attempt after another toconquer this weedy turfgrass. Eachtime a new weapon has come along,word has spread quickly that Poaannua has finally been defeated.Unfortunately, these dispatches fromthe war zone are always premature.

Golf -courses the world over aretheaters of operations in this war. Theonly areas where annual bluegrassisn't a problem are some warm,remote tropical island courses wherePoa annua hasn't thrived and somecool-region golf courses where super-intendents have nearly achievedpeaceful coexistence with the intruder.

The weapons against Poa annuahave included herbicides, growth reg-ulators, management practices andeven natural biological controls. Butsome of the most effective weaponsagainst Poa annua have proven toohazardous to the human combatantsand have been banned. Otherweapons have inhibited or killed onlycertain types of Poa annua, and leftalive surviving types thp.t producedlegions of seeds to replace the weak-ened troops.

Annual bluegrass is such an aggres-sive invader of turf, I used to jokingly

tell students that it could infest artifi-cial turf. Then I found an artificial-turfpractice tee on a Rorida driving rangethat had annual bluegrass growing infibers where sand had accumulated.Of course, selective control in artifi-cial turf would be no problem, buthistory tells us that selective removalof annual bluegrass from living peren-nial turf is difficult indeed.

Winter annualPoa annua readily produces solid

stands of turf. But it generates profuse

seed heads in spring that create anuntidy playing surface, particularly ongolf greens. And in the heat of summer,the species typicallydies off completely,leaving gaps in the turf until it growsback from seed weeks later.

No superintendent appreciatesdead greens or fairways in midsum-mer, but when annual bluegrass dieson the golf course during heat stress,it's doing exactly what it's supposedto do as a winter annual. -Winter

Continued

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Golf Course Management / November 1996 49

annuals' seeds germinate in late sum-mer and fall. The plants mature in thefall and live through the winter. In thespring, winter annuals produce theirseed crops and die soon thereafter.

Poa annua's winter-annual lifecycle is a natural survival mechanismthat allows this seemingly fragilespecies to simply avoid the stress ofsummer by producing a seed cropand dying. Unfortunately, this is a bigproblem for the game of golf, and thismechanism of survival is one of thereasons this species has been so hardto control.

Some researchers have arguedthat annual bluegrass, with a reputa-tion for weakness because it dies soeasily in stress periods, is actually amuch better competitor than creepingbentgrass in many situations (25). Infact, if an area is seeded to creepingbentgrass and everything possible isdone to maintain that species, annualbluegrass still finds a way to infest thearea. It may be susceptible to stress,but it's one of the most competitivespecies golf course superintendentsdeal with when conditions are rightfor its growth. Even so, annual blue-grass also is quite susceptible towinter damage and may be killed bydirect freezing of the crown (2) and byextended periods under ice cover.

Annual bluegrass invades anyopening in the turf. Although classi-fied as a winter annual, its seed maygerminate almost anytime soil tem-peratures and moisture levels areright. Dormant seed can remainviable in the soil for six years orlonger (18). Whenever a divot, ballmark or similar opportunity presentsitself, annual bluegrass seed is thereto fill in the open area. Althoughmost seed heads are formed in thespring, some seed heads can usuallybe found anytime annual bluegrass isactively growing. This species is alsoknown for its ability to produce seedat very low mowing heights - as lowas lho inch.

While other golf course grasses rarely grow tall enough to produce play-disrupting seed heads, annualbluegrass cannot be mowed short enough to eliminate its seed heads. Here, Poa annua's light-coloredseed heads mar a putting green.

BLUEGRASS from p. 49

Not just one Poa annuaThe grass that is known as annual

bluegrass is really a highly diversegroup of different biotypes with vary-ing characteristics. There are annualbluegrasses that act as true winterannuals. They live through the falland winter, produce a seed crop inthe spring and die no matter howthey are managed. These types aretermed Poa annua annua (3).

There are also types that act asweak perennials. After they producea flush of seed heads in the spring,these "annual" bluegrass plants canbe kept alive through summer byminimizing stress conditions. Thesetypes are known as Poa annua rep-tans (22). Between these twoextremes are hundreds or perhapsthousands of biotypes, some closerto the annua types and some closerto the reptans. In the United States,perennial types are most commonin northern regions, and the annualtypes are more common in south-ern regions. It's typical to find amixture of biotypes on the samegolf course. Superintendents oftenreport variations in color, texture,date of seed-head production and

other visual characteristics amongannual bluegrass patches found ontheir course.

Over the past 17 years, it hasbecome clear that certain biotypeswill segregate based on the conditionsunder which they are managed. Onolder courses, it is not unusual to finddistinct biotypes that are common tofairways, others that are common togreens, and yet other to tees. It is alsopossible to find variable types withineach area (17, 27). This helps explainthe variations in response to chemicalapplications that are often observedfrom one location to another on thesame course.

Mechanical controlOne of the earliest references to

control of annual bluegrass was pub-lished in 1922, before selectiveherbicides had been developed. Pub-lished in Bulletin of the GreenSection of the USGA (1), the articlerecommends mechanical control byremoving annual bluegrass with aknife whenever it begins to invadethe turf.

This article reports that W.A.Alexander, superintendent at Old Elm

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50 Golf Course Management / November 1996

Annual bluegrass easily dies of summer heat stress, then vigorously regrows from seed, only to dieagain the following summer. The result can be large dead patches on the golf course during theplaying season.

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Club, had successfully removedannual bluegrass from his greens overa 10-year period (note that he startedhis control program in 1912). Mr.Alexander said, "Poa annua is allabout us in every direction. All of thegolf courses in our locality have Poaannua on one-half to all of theirgreens. Some of the courses havenothing but Poa annua on theirgreens, and of course have relativelypoor greens for a month or twoat least."

Mechanical control is by no meansoutdated, and it may even be making acomeback in popularity. Many super-intendents who begin with new greens- or who have killed off Poa annuaseeds in their greens through methylbromide fumigation - attempt toremove every invading plant as itappears. While this can be practicedsuccessfully for a time, annual blue-grass usually wins the final battle.

ArsenatesThe first selective controls for

annual weeds, the arsenates, weredeveloped in the late 1920s. Theiruse for annual bluegrass began exper-

Golf Course Management / November 1996

imentally in 1930 (21). These arsenic-containing materials included arsenicpentoxide, lead arsenate and, calciumarsenate. Interestingly, these first her-bicides were some of the mosteffective controls ever developed forannual bluegrass.

Arsenic is chemically very close tophosphorus, an essential nutrient ele-ment known for its immobility in thesoil and for its importance at the timeof establishment. Arsenic is so similarto phosphorus that the root system ofa germinating plant will take it up.Although arsenic is similar to phos-phorus, it cannot function likephosphorus in the plant. Instead it's adeadly poison that quickly kills theseedlings and mature plants at higherrates. Because it's immobile, arsenicremains near the surface after it'sapplied. Established grasses with awell-developed root system, such ascreeping bentgrass on a fairway, willobtain phosphorus from the underly-ing soil, while the germinatingseedlings of annual bluegrass arekilled at the surface by arsenic.

Proper use of arsenic took agreat deal of management skill (9).

The selectivity is based on concen-tration. If the level is too high, it willkill the perennial grasses, as well asthe weeds. The tricalcium arsenatewas particularly phytotoxic in lowareas and in anaerobic conditions.Arsenic is an element and doesn'tbreak down into nontoxic materialsas do modern organic herbicides. Ifmistakes in application were made,damage to the perennial turf wouldlast for years. I visited an Ohio golfcourse in 1975, 10 years after cal-cium .arsenate had been mistakenlyapplied at 10 times the prescribedrate. Damage to the grass could stillbe seen during stress periods oflate summer ..

It wasn't the potential of turf dam-age that eventually removed thesematerials from the market; it was therisk of human exposure. Arsenic isextremely toxic to humans and wasremoved from the market in theearly '70s. It made a brief comebackin the early ,80s (13), but restrictionsmade it difficult to use. Arsenic is nolonger available in the United Statesfor control of annual bluegrass,although a few courses may still havesupplies that were purchased beforethe material was removed from themarket.

Organic preemergenceherbicides

The next answer to the annualbluegrass problem was the organicpreemergence herbicides that beganto reach the market in the '60s (16,23). These materials, such as ben-sulide (sold as Betasan and Pre-San),DCPA (Dacthal) and pronamide(Kerb, for warm-season grasses)would selectively kill germinatingseedlings of annuals while doing littledamage to established perennial turf.They were safer than the arsenicalsfor the turf and were safer for humansto use. The solution seemed simple.This is an annual species. If you could

Continued

51

Growth regulatorsThe '60s also brought the first

appearance of growth regulators tocontrol Poa annua, in which theywere used to inhibit seed formation.These materials made anotherappearance in the '80s when theywere used to selectively phase outannual bluegrass.

selectively kill the germinatingseedling, eventually annual bluegrasswould be eliminated.

Thirty years later, annual bluegrassis with us still, even though thesechemicals are good at killing Poaannua seedlings if levels of activeingredient are high enough. Theproblem is that not all annual blue-grass is a true winter annual. Thereare many perennial types that pro-duce seed but do not have to comeback from seed each year. Preemer-gence herbicides have no affect onmature plants because they killonly atthe time of germination.

A second problem is that theseorganic materials break down in thesoil. Their period of efficacy is 30 to 60days, depending on weather conditions.The primary period for annual blue-grass germination is in late summer, butit may germinate anytime there is anopening in the turf. It's not feasible tokeep the level of these materials highenough throughout the season to pre-vent germination into divots, ball marksand other openings. This was the bigadvantage of the arsenates. Their effi-cacy period could be maintained allseason because they were inorganicand wouldn't break down.

The search for new and better pre-emergence herbicides continuestoday. Dithiopyr (under the brandname Dimension) has recently beenlabeled as an annual bluegrass control,and it has been shown to be effectivein some situations. There will be oth-ers in the future, but it is evident thatpreemergence herbicides will not bethe final answer to the problem.

BLUEGRASS from p. 51 Growth-regulating compounds suchas maleic hydrazide (a component ofPo-San) and mefluidide (sold asEmbark) are good seed-head inhibitors.Theoretically, if seed production couldbe stopped, the seed source would beeliminated and eventually the annualbluegrass would disappear.

It sounded good, but unfortunatelyit didn't work. There were two prob-lems. First, there are many perennialbiotypes of annual bluegrass, and asimple elimination of the seed sourcefor a season or two had little impacton these grasses. The other problemwas the almost inexhaustible supply ofannual bluegrass seed that alreadyexists in the soil beneath older turf-grass stands. This seed can remainalive for years, awaiting an opportu-nity to germinate.

In the '80s, mefluidide made a briefcomeback with a slightly differentapproach. It was promoted as a seed-head inhibitor, but this time the ideawas to nurture the annual bluegrass asturf. The goal was to allow the plant touse the energy that would normally gointo seed-head production to enhanceits likelihood of survival during thestress periods of midsummer. This wasa good idea and showed some promiseof success. The problem was timing.Mefluidide had to be applied at just theright time to be effective. It quicklybecame apparent that the timing wasdifferent for a south-facing slope thanfor a north-facing slope. The differentbiotypes of annual bluegrass also var-ied over several weeks in theirseed-head production.

Mefluidide also has been used inrecent years to prevent seed-head for-mation on annual bluegrass in thespring to improve putting quality ongolf course greens. The label for thisuse is somewhat unclear, however.The label on the product sold asEmbark Lite doesn't restrict its use ongolf greens, unlike the label on otherEmbark formulations. Some turf dis-coloration can occur from mefluidide,and label recommendations should befollowed closely.

Endothal could either be classifiedas a growth regulator or as aherbicide. It has growth-regulatingcharacteristics at low rates of applica-tion. At the higher rates used forannual bluegrass control, it works as aherbicide that kills the living plant. Itwas used as a postemergence controlfor annual bluegrass in both Kentuckybluegrass and creeping bentgrass inthe early '70s (23). At higher tempera-tures endothal tended to kill desirableperennial grasses. Some annual blue-grass biotypes were extremelysensitive to it, while others were toler-ant. Researcher A.J. Turgeon, Ph.D.says it also worked well on sandy soils,but required high levels on organicsoils. Endothal was available in thePacific Northwest for annual bluegrasscontrol into the '90s. While it's nolonger being sold there, remainingstocks can be used, and there aresome golf courses still using it.

Fenarimol, a growth-regulatingcompound that was released as thesystemic fungicide Rubigan, waslabeled as a control for annual blue-grass in the '80s (24). Selectiveinhibition of Poa annua by this chem-ical reportedly allowed perennialgrasses to eventually crowd it out.This phenomenon proved to work ononly certain biotypes, and annualbluegrass control was eventuallydeleted from the label, although fena-rimol is still used in the southernUnited States for selective preemer-gence control of the annual biotypesin dormant warm-season turf.

Gibberellic acid inhibitorsFlurprimidol (Cutless), paclobutra-

zol rrGR) and trinexapac-ethyl (Primo)represent the next step in the use ofgrowth-regulating compounds tophase out annual bluegrass. Thesecompounds suppress growth by inter-rupting the plants' ability to synthesizethe hormone gibberellic acid. Theiruse began in the '80s and continuesto the present. These gibberellic-acidinhibitors slow the growth of annualbluegrass, but have less affect on com-

52 Golf Course Management / November 1996

Continued

biotypes has limited their effective-ness. Research in 1983 revealed thatsome biotypes can tolerate high ratesof triazine applications (10). Triazinesalso affect the success of winter over-seeding with cool-season species.

Glyphosate (sold as Roundup, Hoe-down and Avail) is a nonselective,systemic, postemergence herbicidethat will kill annual bluegrass andalmost any other grass it comes into

Annual bluegrass is a winterannual, cool-season grass. Itsboat-shaped leaf .tip and foldedvernation distinguish it fromcreeping bentgrass, which has apointed leaf tip and rolled verna-tion. It can be distinguished fromKentucky bluegrass - which alsohas a boat-shaped leaf tip <andfolded vernation - by its long,;membranous ligule. Bermuda-grass, with its pointed leaf tip andhairy ligule, is easilydistinguishedfrom annual bluegrass.

Annual bluegrass is generally a bunch grass, but some bio-types may have short stolons. Colonies may have a lighter:color than surrounding turf, although that is not always .thecase. The species generally produces seed heads, althoughsome biotypesproduce few,if any. Manybiotypes per-sist as weakperennials,not true win-ter annuals.

CharacteristicsofRoa annua

,7Osand was used for a period of timewith some success (14). Inconsistencyof plant response led to its removalfrom the market a few years later.

Triazine herbicides are known fortheir ability to selectively kill cool-sea-son grasses in warm-season turf. Thisshould be a perfect mechanism foreliminating the cool-season annualbluegrass from bermudagrass, awarm-season grass. These materialshave been used with some success,but again the old problem of resistant

Postemergence herbicidesOver the past 30 years, several

herbicide labels have promisedannual-bluegrass control on golfcourse turf. Many of those productshave since disappeared from the mar-ket, and others have simply notproven effective on annual bluegrassin perennial turf.

Linuron was labeled in the late

peting cool-season, perennial grassessuch as creeping bentgrass. The netresult is a slow conversion away fromannual bluegrass to the desirablespecies (26).

Trinexapac-ethyl is the newest ofthe three materials. In a 2-year test onfairways on two golf courses in Wis-consin, researcher Frank Rossi, Ph.D,observed a 8.5-percent to 18.7-per-cent reduction in annual bluegrasswith trinexapac-ethyl over a 2-yearperiod (19). Gibberellic-acid inhibitorsdo not-act as herbicides but as growthregulators that slowly phase out theannual bluegrass. They tend to workbetter at fairway height than at greenheight. Management techniques unfa-vorable to Poa annua are animportant part of the process.

The gibberellic-acid inhibitors canplaya role in an integrated programto reduce annual bluegrass, but theyshould be tested first in a side-by-sidetrial with an untreated area to be surethat they are providing the desiredresult on the annual bluegrass bio-types in the environmental conditionsthat exist on your site. Turf responseto growth-regulating compounds canvary with soil type, climatic condi-tions, moisture levels, time ofapplication and a variety of other fac-tors (7). It's also very likely that thedifferent biotypes of annual bluegrassvary in their responses to these mate-rials. They may work on the coursedown the road but not on yourcourse. One other word of caution:Rate of application is extremelyimportant. Follow the label carefully.This is one of those situations wheremore is definitely not better.

Golf Course Management / November 1996 53

contact with. It's often used in renova-tion of areas infested with weedsbefore re-establishment of a newgrass cover. It has no soil activity,however, and will not prevent germi-nation of annual bluegrass seed in thesoil. A common complaint of superin-tendents using this product is thatthey end up with just as much annualbluegrass as they started with.

Glyphosate is quite effective forselectively killingannual bluegrass dur-ing winter in dormant bermudagrassand zoysiagrass, although you mustavoid treatments as the warm-seasongrasses emerge from dormancy.

Ethofumesate (sold as Prograss) islabeled for annual bluegrass controland is getting a lot of attention. It pro-vides excellent postemergence andsome preemergence control. It's par-ticularly useful in perennial ryegrassbecause of the species' tolerance ofethofumesate, even in the seedlingstage. In parts of the country wherethe climate is suitable for perennialryegrass on fairways and tees, theexisting turf can be killed withglyphosate, re-established to rye andthen treated with ethofumesate tokeep the annual bluegrass frombecoming re-established (4).

Ethofumesate is also labeled fordormant bermudagrass overseededwith p'erennial ryegrass (6), although itmay delay the bermudagrass' springgreen-up. Creeping bentgrass andKentucky bluegrass are more sensitiveto ethofumesate, but it can be usedwhere these species are maintained athigher mowing heights, such as fair-ways. Consult the label for warningsabout its use on bentgrass cultivars.It's not labeled for creeping bentgrassgreens, although some superinten-dents have been experimenting withit. Some of our tests on Penncrosscreeping bentgrass greens at theVeenker Memorial golf course here atIowa State University have beenpromising. Other tests have produced

The lighter color on the left side of this practice green reveals a high annual bluegrass population. Theright side has been treated with the growth regulator paclobutrazol.

BLUEGRASS from p. 53

damage to the bentgrass. One thingwe learned the hard way: Never applyethofumesate to bentgrass greens thathave also been treated with thegrowth regulator paclobutrazol. ThePrograss label states that ethofume-sate should not be applied withineight weeks following the applicationof growth regulators. This material isrelatively new, and whether the oldproblem of biotype resistance willrecur is still open to speculation.

Methyl bromide is a nonselectiveherbicide that is applied as a gasunder plastic covers placed over theturf. The covers are left on the turffor a minimum of 48 hours. The gasfilters down into the soil, and thematerial will kill not only maturetissue, but also the seed lying dor-mant in the soil. Methyl bromide, ifused properly, represents the onesure way of killing mature annualbluegrass and of preventing its rein-festation from seed (8).

This material is difficult to use andmust be applied by specialists with theproper equipment and know-how.Special certification is required for itsuse. All grass is killed and completere-establishment is required, which

means that the treated area will likelybe out of play for months.

Methyl bromide is also expensive,with the application of the gas cur-rently running 8 to 14 cents per squarefoot, and total renovation costing up to$1,000 per green. Golf course use hadbeen traditionally limited to greens andtees. As methods have developedfor treating larger areas, however, itsuse has expanded to fairways.Superintendents generally seem quitepleased with the results of methyl bro-mide fumigation. Minor infestations ofannual bluegrass may persist in a fewareas where the gas is not uniformlydistributed, but on most areas the con-trol is usually complete. Vigilance iskey to success following methyl bro-mide fumigation. The process ofreinfestation from surrounding areaswillbegin almost immediately, and youmust remove every invading annualbluegrass plant to prevent the problemfrom returning.

There's political pressure to banthe use of methyl bromide nationwidebecause of suspected damage to theatmosphere's ozone layer. It will beavailable through at least 2001 as theevaluation process continues.

54 Golf Course Management / November 1996

ExperimentationSeveral experimental herbicides

with potential for controlling Paaannua were dropped from considera-tion after they were widely tested. Inthe mid-'80s, I worked with a productthat appeared to have great potentialfor selectively removing annual blue-grass from both Kentucky bluegrassand creeping bentgrass turf. Afterconducting some successful tests on alocal golf course, I moved to anothercourse 50 miles away that had adifferent biotype of annual bluegrass.There, 12 times the effective herbi-cide rate didn't even discolor thelocal biotype.

The perfect herbicideWhat characteristics would define

the perfect herbicide for control ofannual bluegrass? It would have bothpostemergence and preemergenceactivity on annual bluegrass. It wouldbe unIversallyeffective on all biotypes.It would do no damage to creepingbentgrass, Kentucky bluegrass, peren-nial ryegrass, bermudagrass or anyother desirable turfgrass species. Itwould be nontoxic to humans andwould carry no risk to groundwater orsurface-water resources. It's highlyunlikely that such a material will everbe developed. The biggest barrier isthe tremendous genetic diversity thatexists within the species we call Poaannua. If something were developedthat would eliminate 99 percent of it,the remaining 1 percent would reinfestthe area in a few short years, and wewould have to look for a new solution.

Making friends with Poa annuaThe next attempts to deal with

annual bluegrass reflect an "if youcan't beat it, join it" philosophy. The,50s and '60s were times of opti-mism. New discoveries were beingmade every year, and the release ofnew herbicides led to the belief thatthe end of the annual bluegrass prob-lem was just around the corner. Bythe end of the '60s and the early

Golf Course Management / November 1996

'70s, though, some doubts werebeginning to emerge. Country clubmembers were growing a little wearyof the extreme treatments used toeliminate this troublesome grass, suchas these efforts in 1967 at theKnickerbocker Country Club inTenafly, N.J. (20): "The nearly 100percent Poa annua fairways weretreated with MCPP (mecoprop) at thehighest recommended rate, thentreated twice with sodium arsenateand thatched. The fairways were thenscorched and seeded with a bentgrassmixture at 100 pounds per acre."

By the early '70s, strategiesemerged for maintaining annual blue-grass in the best possible conditionfor play (28). Annual bluegrass is nottotally objectionable. At some timesof the year, it can provide a high-qual-ity playing surface. Its biggestproblems are the seed heads, particu-larly in the spring, and the fact that ittends to die in stress periods.

The careful use of growth-regulat-ing compounds can help with theseed-head problem, but keepingannual bluegrass alive can be a littlemore difficult. Climate is the key. Inthe cooler regions of the northernUnited States and in some microcli-mates such as mountain areas, coastalareas and the foothills of the Rockies,this approach can be successful. In theGreat Plains and the transition zone,where heat and drought are common,annual bluegrass management maynot be successful.

The rules of managing annualbluegrass as a turf species are simple:Take everything you know aboutproper management to preventannual-weed infestation and do theopposite. Irrigation frequency, forexample, can either encourage or dis-courage annual species. Annuals relyon germination of seed on the soil'ssurface for survival, while deep-rooted perennials receive theirmoisture from the underlying soil. Toencourage an annual, keep the sur-face wet.

Fertilization can also playa role.Nitrogen levels should be maintainedon the high side, as should phospho-rus, which is particularly important inseedling establishment (5). One man-agement step that discouragesannual weeds is to keep low phos-phorus fertilization levels on thesurface and allow the mature turf totake its phosphorus from the under-lying soil. A soil test will revealwhether the underlying soil has suffi-cient phosphorus.

Spoon feeding should be. used inspring, just after seed heads haveformed, to strengthen the turf for thesummer-stress period. Spoon feedingshould also be used in the summer tojust meet the needs of the turf. Heav-ier fertilization can be used in fallwhen annual bluegrass is thriving.

The timing of cultivation can alsofavor annual bluegrass. To discourage aweed crop, cultivationis timed to avoidpeak seed germination. For crabgrasscontrol, for instance, the spring germi-nation period is avoided, and aerificationis instead timed in late summer or fall.The peak germination period for annualbluegrass in most regions is late summerand fall. If the goal is to encourageannual bluegrass, aerification in mid- tolate August willbring seed to the surfacefor germination.

Some mowing practices canencourage annual bluegrass. light-weight mowing equipment andclipping removal are not helpful tothe species, but lower mowingheights favor Paa annua, particularlythe extremely low mowing heightsused on greens.

The preventive fungicide programrequires materials nontoxic to annualbluegrass. Fenarimol, which is knownto have some activity on annual blue-grass, would not be a good choice forencouraging annual bluegrass sur-vival. Also avoid growth regulatorsthat inhibit gibberellic acid. Insectcontrol will likely be necessary. Black

Continued

55

turfgrass ataneius should be givenclose attention if annual bluegrass isthe primary turf.

Integrating controlsOne of the ultimate challenges for

a superintendent is to combine all theaccumulated knowledge about annualbluegrass into an integrated programto discourage Poa annua and encour-age perennial .turf. While thisapproach began in earnest in the,80s, its origin dates back much ear-lier (9, 12, 16). This requires a greatdeal of knowledge and skill.

Creeping bentgrass fairways arethe primary turf on which this methodis used, but the basic principles wouldapply to any type of perennial turfsystem with an annual bluegrass infes-tation. It has become popular in themidwestern and northeastern regionsof the United States, particularly inareas where the high temperature andhumidity of summer make annualbluegrass maintenance impractical. Inthis case, management practices areused to eliminate the annual blue-grass, not to encourage it.

Irrigation again plays an important

BLUEGRASS from p. 55 role, only this time it's going to be lessfrequent to allow drying on the sur-face. This practice favors the relativelydeep-rooted perennial grasses andhelps select against the annual blue-grass. Syringing - the application ofsmall amounts of water during middayhigh temperatures to cool the grassand wash sugars and amino acidsthat have formed on the cuticle - iscritical in summer. Nitrogen andphosphorus are maintained atmoderate levels to just meet therequirements of the perennial grasswithout promoting competing weeds.

Mowing is a critical part of theprogram. Experience has shown thatlightweight mowers tend to help withthe conversion process by favoringperennials such as creeping bent-grass, whereas heavier mowingequipment tends to favor annual blue-grass. Clipping removal is also animportant part of the process (11,29). This is likely due in part to theremoval of seed produced by theannual bluegrass, although this can'texplain all of the benefits observedwhen clippings are removed ..

Cultivating strategically to discrimi-nate against annual bluegrass is a littlemore difficult. Compaction favors

annual bluegrass, and aerification willallow the perennial turf to be morecompetitive. However, aerificationalso brings annual bluegrass seed tothe surface and can encourage a weedproblem. Trying to avoid the primarytimes of seed germination would bethe obvious solution. That is difficultto do, however, because this also hap-pens to be the l?est time to aerify.Disruption of play may also be a fac-tor, and the timing of aerification tothe best advantage may be difficult.It'sclear that late summer is a time thatfavors winter annuals and should beavoided. There is too much stress inmidsummer. Although annual blue-grass se~d will also germinate in thespring if conditions are right, springand fall aerification with the properuse of pre emergence herbicides areprobably the best alternatives in mostsituations. Spiking may also play animportant role. Spiking severs stolons,resulting in rooting from the nodes.This provides a competitive advantagefor perennial turf.

More and more turf managers areoverseeding per~nnial turf as part oftheir annual bluegrass control pro-gram. Particul<ilrly where creepingbentgrass is the'desired species, seed-

56 Golf Course Management / November 1996

ing can help thicken the turf and mayhelp overcome annual bluegrass' com-petitive advantage in seed production.

Growth regulatorsand herbicidesmayalso be an important part of the process.They must be used in accordance withsound management techniques, but theymay give the perennial turf the edge itneeds to outcompete the Poa annua.

Biological controlThe concept of biological control

is relatively new, but it may welldevelop into a common part of pestmanagement in the future. It mayinvolve biologkal pests that selectivelykill annual bluegrass without damag-ing perennial turf. One such materialis a bacteria named Xanthamanascampestris (30). While early tests onPaa annua annua types are showingsome promise, the bacteria has beenless effective on perennial biotypes.

What the future holdsThere was a time when I had a

great deal of hope that science wouldfind an answer to the annual blue-grass problem. For me, that time haspassed. There will be advances andimprovements in technology, but I ambetting that this aggressive, highlydiverse species will find a way aroundevery one of them.

Years before I was born, golfcourse superintendents were holdingmeetings to discuss this problem. Allthrough my career it has been one ofthe primary focuses, of attention inthe golf industry. If I had to predictthe future, I would bet that 50 yearsafter this generation has passed, Paaannua will still be a problem.

That may not, however, be as badas it sounds. If a country club's mem-bership wants to see playing conditiondeteriorate quickly, it simply needs toreplace an experienced superinten-dent with someone less skilled inannual bluegrass management.

If a "magic bullet" were developedtomorrow that would kill all annualbluegrass, superintendents' liveswould be easier, but their skills and

Golf Course Management / November 1996

knowledge would become less valu-able. This old enemy may be more ofa friend than we realize. D

Literature cited1. Alexander, W.A. 1922. How we con-

trolled Poa annua at Old Elm. Bulletin ofthe Green Section of the USGA2(7):213-214.

2. Beard, J.B., and c.R. alien. 1963. Lowtemperature injury in the lower portionsof Poa annua L. crowns. Crop Sci.3:362-363 ..

3. Beard, J.B., P.E. Rieke, AJ. Turgeon,and J.M. Vargas Jr. 1978. Annual blue-grass (Poa annua L.) description,adaptation, culture and control. In: Res.Reports 352 from the Mich. State Univ.Agric. Exp. Stn., East Lansing, Mich.

4. Christians, N.E. 1990. The annual blue-grass to rye to bentgrass approach. GolfCourse Management 58(8):36-38.

5. Christians, N.E. 1996. Phosphorus nutri-tion of turfgrasses. Golf CourseManagement 64(2):54-57.

6. Dickens, R. 1979. Control of annual blue-grass (Poa annua) in overseededbermudagrass (Cynodon spp.) golfgreens. Weed Sci. 27 :642-644.

7. Diesburg, K.L., and N.E. Christians.1989. Seasonal application of ethephon,flurprimidol, mefluidide, paclobutrazol andamidochlor as they affect Kentucky blue-grass shoot morphogenesis. Crop Sci.29:841-847.

8. Escritt, J.R., and D.C. Legg. 1968. Inves-tigations on annual meadow grass control.J. Sports Turf Res. Inst. 44:5-18.

9. Ferguson, M.H. 1959. Poa annua con-trol. USGA J. and Turf Management12(5):25-28.

10. Gasquez, J., and H. Darmency. 1983.Variations of chloroplast propertiesbetween two triazine resistant biotypes ofPoa annua L. Plant Sci. Letters 30:99-106.

11. Gaussoin, R.E., and B.E. Branham.1989. Influence of cultural factors onspecies dominance in a mixed stand ofannual bluegrass/creeping bentgrass.Crop Sci. 29:480-484.

12. Grau, EV. 1951. Further suggestions forresearch on Poa annua. USGA J. andTurf Management. 4(5):30-32.

13. Hummel, N. 1982. Beware Poa - Thearsenicals are back. Iowa TurfgrassGrower 6(8):2-4.

14. Ingratta, R.G., G.R. Stephenson, andC.M. Switzer. 1979. Selective control ofannual bluegrass in Kentucky bluegrassturf with Unuron. Can. J. Plant Sci.59:469-473.

15. Jagschitz, J. 1979. Annual bluegrass con-trol in Kentucky bluegrass turf withherbicides. In: Proc. of the NorthwesternWeed Sci. Soc. 33:308-312.

16. Juska, F.V., and A.A Hanson. 1967.Factors affecting Poa annua L. control.Weeds 15(2):98-101.

17. Lush, W.M. 1989. Adaptation and differ-

entiation of golf course populations ofannual bluegrass (Poa annua). Weed Sci.37:54-59.

18. Roberts, H.A, and P.A Feast. 1973.Emergence and longevity of seeds ofannual weeds in cultivated and undisturbedsoil. J. Appl. Ecol. 10:133-143.

19. Rossi, F.S. 1995. Evaluation of annualbluegrass population reduction programsfor annual bluegrass/creeping bentgrassfairway turf. The Grass Roots 13(2):34-36.

20. Silvar, R. 1967. Scorched earth at theKnickerbocker. USGA Green SectionRecord 4(6):19.

21. Sprague, H.B., and G.W. Burton. 1937.Annual bluegrass (Poa annua L.) and itsrequirements for growth. N.J. Agric. Exp.Bull. 630.

22. Timm, G. 1965. Biology and systematicsof Poa annua. Feitschrift fur AckerundPflanzenbau. 122(3):267-294.

23. Turgeon, A.J. 1974. Annual bluegrasscontrol with herbicides in cool-season turf-grasses. p. 382-389. In: E.C. Roberts(ed.). Proc. 2nd Int. Turfgrass Res. Conf.Soc. Agron., Madison, Wis.

24. Environmental Protection Agency. Rubi-gan product information bulletin on Poaannua. USEPA experimental-use permitNo. 1471-EUP-50. U.S. Gov. Print.Office, Washington, D.C.

25. Vargas, J.M. 1996. Annual bluegrass: Afierce competitor. Golf Course Manage-ment 64(2):49-50.

26. Watschke, T.L. 1996. Growth regulatorsand Poa annua. Turfgrass Trends5(3):1-4.

27. Wu, Un. 1991. Turf management effectson genetic structure and adaptation of golfcourse Poa annua populations. HortSci.26(6): 716.

28. Zhou, T., and J.C. Neal. 1995. Annualbluegrass (Poa annua) control withXanthomonas campestris pv. poannuain New York State. Weed Tech.9(1):173-177.

29. Zontek, S.J. 1973. A positive approach toPoa annua management. USGA GreenSection Record 11(4): 1-5.

30. Zontek, S.J. 1983. They are mowing fair-ways with triplex mowers and picking upthe clippings, too! USGA Greens SectionRecord 21(1): 1-5.

AcknowledgmentsStan Zontek of the USGA provided useful

information for preparation of this article.

Nick Christians specializes in turfgrass sci-ence in the Horticulture Department at IowaState University. He has worked as a golfcourse superintendent, assistant superinten-dent and grounds manager. He has a Ph.Dand master's degree in agronomy from OhioState University, and a bachelor's degreefrom Colorado State University's Schoolof Forestry.

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