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In the real world, these grasses aren't so tolerant of low mowing after all.

These varieties have greater shoot den-sities (compared with the old standby,Tifdwarf), a perceived ability to allowfaster putting speeds and tolerance oflow mowing heights (7). These newvarieties have also helped alleviate con-cerns about Tifdwarf, as producers havefocused on delivering the new cultivarsin contaminant-free plant material ofknown origin.

Considering these merits and thefact that a new putting green bermuda-

Diseases and heat besiegeultradwarf bermudagrasses

J. Bryan Unruh, Ph.D., and Steve Davis

Over the past decade, several newbermudagrass (Cynodon species andhybrids) varieties have been developedfor putting greens in the southeasternUnited States. Most notable are the newhybrid "ultradwarf" bermudagrass vari-eties, including Champion, FloraDwarfand TifEagle.

These new varieties were developed,in part, to provide superior bermuda-grass putting greens, rivaling those ofcreeping bentgrass (Agrostis palustris).

More Info: www.gcsaa.org

• Although ultradwarfbermudagrasses weredeveloped for lowermowing heights, theycan better endure stressif mowing heights areabove the minimum .

• With ultradwarfs, fixingone problem often leadsto another problem .

• All ultradwarfs appearequally susceptible tostress-related decline.

Spring--.dead spot on an ultradwarf putting green during the spring ..........\

Golf Course Management • April 2001 49

grass variety had not been releasedin more than 30 years, the new ultra-dwarf bermudagrasses enjoyed wideacceptance with many "success" storiespublished (1,10,11). However, lesshas been written on the many unsuc-cessful experiences superintendentshave had with these ultradwarfbermudagrasses.

The golf course superintendent,general manager and green committeemust seriously consider the re-quirements of growing an ultradwarfbermudagrass before the new variety issprigged into the putting surfaces.Champion, FloraDwarf and TifEagledemand complex management prac-tices that are not fully understood andthat sometimes seem directly in conflictwith each other.

This article is based on observationsof the past several years, but mostparticularly on the results of a scout-ing program sponsored by AventisEnvironmental Sciences during thesummer of 2000 on more than 70 golfcourses across the panhandle of Florida,into Mississippi and Louisiana andnorth to Montgomery, Ala.

All of the monitored courses hadultradwarf putting greens, mostlyChampion, FloraDwarf or TifEagle,that were experiencing some level ofdecline in quality. The age of the turf on

Close-up of spring dead spot on an ultradwarf putting green during the spring.

the monitored putting surfaces rangedfrom newly sprigged to 4 years old, andthey were being mowed at heights rang-ing from 0.110 to 0.130 inch.

Low-mowing fatigue?Although the ultradwarfs can toler-

ate low mowing heights, they do sufferstress under aggressive mowing,although this is not a widely acceptedunderstanding. Ultradwarf canopy tem-peratures during the hottest months of2000 reached 142 F. Although bermuda-grass is a warm -season species, it cannotmaintain good quality at this canopytemperature. Our observations haveshown that raising the height of cutfrom 0.115 to 0.130 lowered canopytemperatures as much as 30 F.

Therefore, the main recommenda-tion for ultradwarf greens under thestress of the summer heat is to increasethe height of cut.

But here is a paradox: Superintendentsand architects choose an ultradwarfbecause it is supposed to tolerate lowmowing heights and thus support supe-rior putting surfaces. As unfavorablegrowing conditions require raisingmowing heights, the desired attributesof the ultradwarf varieties diminishor disappear.

Diseases inflict damageBermudagrass requires full sunlight

to produce the best-quality turf.During the rainy season in Florida orwhen cloudy conditions dominatesoutheastern U.S. weather patterns,bermudagrass quality dramaticallydeclines. The disease known asbermudagrass decline (Gaeumannomycesgraminis var. gram inis) tends to flourishunder these stressful conditions.

Although the morphology of theultradwarfs features one to two timesthe number of shoots per square inch ofTifdwarf (6), they can't always outgrowGaeumannomyces infection (4). As withTifdwarf, little relief is gained fromfungicide applications. Again, inc~eaS:'ing the mowing height provides)hebestrelief. Again, that practice negates the

50 Golf Course Management • April 200 1

Curvularia blight on an ultradwarf putting green during early summer.

varieties' most -desired attributes.During the very hot summer

drought of 2000, two additional diseasesinflicted widespread damage on ultra-dwarf bermudagrass putting greens.

Spring dead spot (Ophiosphaerellaherpotricha) and curvularia blight(Curvularia species) - alone and incombination - depleted maintenancebudgets and decreased putting greenquality on more than 70 golf courses,say two experienced pathologists. LarryStowell, Ph.D. (Pace Consulting,San Diego), and Phil Colbaugh,Ph.D. (Texas A&M University), pro-vided expert diagnoses for the monitor-mg program.

On the greens monitored, springdead spot was the most prevalent dis-ease early in the growing season,whereas curvularia blight was the dom-inant pathogen from late springthrough late fall. Both of thesepathogens had the greatest impact onlower-mowed ultradwarf greens (withmowing heights of 0.130 inch), result-ing in a major loss of turfgrass vigor anddensity, while creating sunken patternsand patches in the putting greens. Inaddition, Pythium blight was seen latein the season.

Curvularia blight is known as dog

footprint in Japan. Its typical symptomsare brown, circular patches with a diam-eter of 2-8 inches, about the size of adog footprint (9). As the diseasespreads, the spots coalesce to formirregular patches. These pathogensaffect the oldest leaves, causing yellow-ing of the mat under new leaves.

The fungus grows at cut tips or sur-face wounds caused by aerification, ver-ticutting and mowing (managementpractices that are essential to properultra dwarf thatch management). Underthe monitoring program, curvulariablight was the pathogen most oftendiagnosed as the primary concern,according to Stowell.

Many would say that Curvulariaspecies are secondary pathogens thatwill only invade stress-weakenedturf grass damaged by salinity, low mow-ing heights, traffic, root pathogens ordysfunctions, nematodes, drought, her-bicide injury or growth-regulatingfungicides. Others continue to debatewhich pathogens are truly present.Although this is mostly an academicdebate, the problem in the field stillexists, and turfgrass managers must stilldeal with the problem.

Spring dead spot is caused by thepathogen Ophiosphaerella herpotricha

Golf Course Management • April 200 1 51

in regions where bermudagrassbecomes dormant annually under coldtemperatures (2). Although spring deadspot reportedly does not occur inFlorida, the courses in the Aventis mon-itoring program frequently experiencethe temperatures necessary for dor-mancy in bermudagrass, and thispathogen has caused severe problems.

As with Gaeumannomyces, raisingthe mowing height - a practiceunpopular with many golf professionalsand club members - may be theonly acceptable answer to these dis-eases. Research is under way to under-stand how to manage these new dis-eases, but definitive results are not yetavailable. Turf managers experiencingthese problems have tried, with somesuccess, syringing during periods ofextremely high canopy temperatures ifa breeze or wind is present to providesurface cooling.

Fungicide programs involvingazoxystrobin (Heritage) have alsoreduced the impact of spring dead spot.Vinclozolin (Vorlan, Curalan, Touche)or iprodione (Chipco 26GT) mayreduce secondary invasion of curvu-laria blight. In replicated trials con-ducted on four of the courses in theAventis monitoring program, no differ-

Curvularia blight on an ultradwart putting green during midsummer.

52 Golf Course Management • April 2001

ences were seen between the fungicidesevaluated when the height of cut wasraised. Others have found thatincreased levels of ammonium sulfatehave improved turfgrass vigor, which isalso vital to reducing the impact of dis-ease symptoms. Raising the height ofcut of the turf appears to provide themost relief and greatest turfgrassimprovement.

Although the ultradwarf varietiesoffer many advantages over conven-tional putting green varieties, severesummer climatic conditions and thesetwo fungi seem to affect the ultradwarfsmuch more than the Tifdwarf puttinggreens. The lower-mowed ultradwarfvarieties appear more susceptible, butlower mowing heights alone may becausing the problem because most vari-eties of bermudagrass have been diag-nosed with these pathogens.

Increased thatch accumulationPerhaps the most notable negative

attribute of these new bermudagrassultradwarf varieties is their profusethatch production. The deleteriouseffects of thatch - such as blockedmovement of nutrients and pesticides,inhibition of drainage, increasedoccurrence of localized dry spot andthe harboring of insects and diseases -are no secret to superintendents.Mandatory cultural practices such asverticutting, topdressing and aerifica-tion rid the turf of this nuisance.Research at Texas A&M showed that theultradwarfs responded differently toverticutting depth and frequency andtopdressing amount and frequency (6).This mirrors what is found in the field,where frequent and light verticuttingand topdressing appear to keep thatchin check (4).

But then there's black layer. Light,frequent topdressing can damage root-zone composition. Black layer occurswhen water infiltration becomesimpeded by different layers within thesoil profile or when sand topdressing islayered over thatch. It appears that thedense growth habit of the ultradwarfs

Curvularia blight on an ultradwart putting green during late summer.

may act as a filter, allowing the finesttopdressed sand particles to passthrough and thereby creating a particlesize differential and subsequent blacklayer (8).

Another management interaction tobe considered is the effect of theincreased ammonium sulfate levels onblack layer formation because sulfurexacerbates black layer problems.Without question, black layer will be amajor problem on ultradwarf bermuda-grass putting greens.

Things to considerAlthough some may disagree, the

ultradwarfs clearly require attentivemanagement. John Foy, director of theUSGA Green Section's Florida Region,summed up an excellent review ofbermudagrass management by statingthat ultradwarfs do require intensivemanagement and thus may not be suitedfor all courses (4). Other researchershave drawn similar conclusions (5).

When considering an ultradwarf toreplace existing turf, one must look atthe budget. Was it adequate for main-taining Tifdwarf or Tifgreen? Did youhave enough trained staff to maintain

the golf course with the "old" grass? Doyou have the equipment and equipmentmanagement staff to support the cur-rent operation adequately? Can (orwill) the club provide the additionalresources needed to properly managethe ultradwarfs?

Managing ultradwarfs requires addi-tionallabor from both the maintenancecrew and the shop. Turf equipmentmanagers must maintain equipmentmore precisely for ultradwarfs. If theequipment manager cannot get amower with multiple cutting units tocut true at 0.125 inch, the results will benoticeable, and there will be trouble.

Because of increased topdressingfrequency, frequent reel grindingand back-lapping will ensue. Thiswill obviously result in increased costsassociated with purchasing reels andbedknives and the needed hardware.Furthermore, golf courses withoutreel-grinding capability must obtainit or avoid using these new varietiesaltogether.

Those wishing to grow ultradwarfswill find that some additional equip-ment may be needed as well. Experiencehas shown that the spinner-type top-

Golf Course Management • April 2001 53

dressers capable of applying smallamounts of sand are best suited forthe routine frequent topdressings.Machines that can adjust the angle ofthrow can propel the sand into theturf canopy. Another piece of equip-ment for managing ultradwarfs is theGraden verticutter, which cuts throughthatch, leaving 'l4-inch-wide grooveswith minimal collateral surface disrup-tion. To date, researchers have not eval-uated the merits of either of these piecesof equipment.

Ultradwarf researchExperience has shown that ultra-

dwarfs require additional and differentmanagement practices comparedwith the industry standards. ManyU.S. researchers are trying to betterunderstand the management needs ofthe ultradwarfs. Because few golfcourse superintendents can afford tokeep a checkerboard of research plotson their putting greens, most ofthis research is conducted on un-stressed turf at research facilities oron practice greens that don't haveenough play to create the stresses foundon golf greens.

Many consumers are driven to havethe latest model of automobile or the

Black layer formation on an ultradwarf putting green.

54 Golf Course Management • April 200 1

fastest, most up-to-date computer. Theultradwarfs are not merely the newmodel year of an old standby. Tradingup to an ultradwarf is like trading theold Chevy for a Formula One race car orthe old Commodore 64 computer for amain frame. When considering anultradwarf, superintendents must beprepared to go the distance to producean acceptable outcome .•

AcknowledgmentsDisease diagnosis for the Aventis monitoring

program was provided by Larry Stowell, Ph.D., ofPace Consulting. Phil Colbaugh, Ph.D., TexasA&M, also provided expert diagnosis.

Literature cited1. Beard, J.B. 1996. Bermudagrass breakthrough:

New cultivars for Southern putting greens.Golf Course Management 64( 12):58-62.

2. Elliott, M.L. 1995. Disease response ofbermudagrass to Gaeumannomyces graminisvar. graminis. Plant Disease 79:699-702.

3. Elliott, M.L. 1999. Disease management.p. 143-156. In: J.B. Unruh and M.L. Elliott(eds.), Best management practices for Floridagolf courses, 2nd ed. University ofFlorida Institute of Food and AgricultutralScience Cooperative Extension Service,Gainesville, Fla.

4. Foy, J.H. 2000. Going for the gold withbermudagrass greens: Part II. USGA GreenSection Record 38(6): 1-5.

5. Guertal, B., and R.H. White. 1998. Dwarfbermudagrasses demand unique care. GolfCourse Management 66(7):58-60.

6. Gray, J.L., and R.H. White. 1999. Maintainingthe new dwarf greens-type bermudagrasses.Golf Course Management 67(3):52-55.

7. Hanna, W. 1998. The future of bermudagrass.Golf Course Management 66(9):49-52.

8. Overbeck, A. 1999. Tests reveal good andbad of ultradwarfs. Golf Course News11(7):1,19,33.

9. Toshikazu, T., and J.B. Beard. 1997. Color atlasof turfgrass diseases: Disease characteristicsand control. Ann Arbor Press, Chelsea, Mich.

10. Westmoreland, J.W. 1998. Another option forSouthern greens. Golf Course Management66(3):64-67.

11. Williams, S. 2000. TifEagle in the real world.Golf Course Management 68(12):78-88.

]. Bryan Unruh, Ph.D., is an assistant professor andExtension turfgrass specialist in the Institute of Foodand Agricultural Sciences at the University ofFlorida. Steve Davis is a senior sales representativewith Aventis Environmental Science.