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UnderstandingBentgrass Dead SpotImportant new information helps managethis recently discovered putting green disease.BY JOHN E. KAMINSKI and PETER H. DERNOEDEN

Bentgrass dead spot (BDS) is arelatively new disease of creepingbentgrass (Agrostis stoloniftra) that

is incited by the fungal pathogenOphiosphaerella agrostis (1). In creepingbentgrass grown on golf course puttinggreens, BDS appears initially as small,

dime-sized spots that may increase upto three to four inches in diameter (2).

DISEASE DESCRIPTIONDuring early stages of disease develop-ment, the spots are reddish-brown orcopper-colored and mimic ball-mark

injury. As the disease progresses, grass inthe center of the spots becomes tan,while leaves on the outer edge appearreddish-brown. Frog-eye patches occur,but they are uncommon. Patches maybe distributed throughout the puttinggreen or they may be localized. Except

Table IBentgrass dead spot infection centers for 20 field-grown Agrostis spp. selections, College Park, Maryland, between 2000 and 2002.

Infection centers per plotX

2000 2001 2002YBentgrass

Cultivar Species 6 Sept. 29 Nov. IS May 16Aug. 18July 16Aug.

AB"f-CRB-1 creeping 27 a-dz II b-e 9 bcd 3 ab 6 abc 22 abcBackspin creeping 18 cde 6fgh 6 cde 2 bcd 2 ef 12 c-fBARAS 8US3 creeping 21 b-e 7 d-h 7 bcd 2 bcd 5 a-f 18 a-dBAR CB8FUS2 creeping 22 b-e 10 b-e II ab 2 bcd 3 c-f 12 c-fBardot colonial 32 ab 6 e-h 4 ef I cd 2 def 9 defBavaria velvet 8f 4h 2f Od 2 def 4fCentury creeping 27 a-d 14bc II ab 3 ab 6 abc 22 abcCrenshaw creeping 17 def 5 gh 6 de I bcd 2 ef 6 efImperial creeping 33 ab 9 c-g 8 bcd I cd 4 b-f 15 b-e

, L-93 creeping 37 a II bcd 10 abc 2 abc 8 ab 26 aPennA-I creeping 33 ab 15 bc II ab 3 ab 9a 25 abPennA-2 creeping 23 b-e 8 d-h 8 bcd 2 bcd 5 a-f 17 a-dPennA-4 creeping 29 a-d 15 b 12ab 3 abc 5 a-e 15 b-ePenn G-I creeping 25 a-e 10 b-f 8 bcd 2 abc 3 c-f 10 defPenn G-6 creeping 29 abc 8 d-h 9 bcd I bcd 4 b-f 23 abPenncross creeping 14 ef 6 e-h 7 bcd I cd 2 ef 7 efPennlinks creeping 17 def 7 d-h 5 de 2 bcd I f 5 efProvidence creeping 24 a-e II b-e II ab 3 abc 4 c-f 9 defSRII19 creeping 22 b-e 10 b-f II ab 2 bcd 3 c-f 18 a-d !SR7200 velvet 32 ab 24a 14a Sa 6 a-d 12 c-f IXDatawere transformed (y + 0.5f'. but pre-transformed means are shown.

IYBentgrassdead spot fully recovered in the autumn of 200 I and data from 2002 represent new infection centers.I

zMeans in a column followed by the same letter are not significantlydifferent (P ~ 0.05) based on the protected least significant IIdifference multiple mean comparison test.

--~---~..._--~_..~_ .......... -_ ....------ -

20 GREEN SECTION RECORD

in severe cases, the patches generally donot coalesce. Sometimes the spots formdepressions or pits in the puttingsurface.

Disease recovery is slow, and in severecases BDS spots will not fully recoverprior to winter. Foliar mycelium (i.e.,microscopic strands of the fungus) isnot observed in the field, but whendiseased plants are incubated underhigh humidity for three to five days, awhite to pale pink foliar myceliummay develop. Unlike other species ofOphiosphaerella that are turf pathogens,pseudothecia (i.e., sexual fruiting bodiesof the fungus) often are found in thefield on dying leaf, sheath, and stolontissues.

NEED FOR RESEARCHThere is little information regarding thebiology of O. agrostis or the relativesusceptibility of bent grass cultivars tothe pathogen, geographic distributionof the disease, or cultural factors associ-ated with BDS outbreaks. Hence, theprimary objectives of this researchwere: 1) to determine the susceptibilityof various field-grown bentgrass culti-vars to O. agrostis; 2) elucidate culturalfactors associated with BDS outbreaks;3) determine the distribution of thedisease in the U.S.; and 4) investigatepseudothecia production, ascosporerelease and germination, and other

Locations ofcreeping bentgrassand bermudagrassconfirmed to beinfected byOphiosphaerellaagrostis between1998 and 2002.

more basic biological properties of thefungal pathogen.

Bentgrass cultivar susceptibility toO. agrostis was assessed on a USGA-specified research green between 2000and 2002 at the University of MarylandPaint Branch Turfgrass Research Facilityin College Park, Maryland. Seventeencultivars and experimental selections ofcreeping bentgrass, two cultivars ofvelvet bentgrass, and Bardot colonialbentgrass (Table 1) were seeded onSeptember 20, 1999.The area was sub-jected to routine cultural practicesthroughout the study (i.e., fertilization,vertical mowing, aeration, and top-dressing). On June 12,2000, all plotswere inoculated with an isolate ofO. agrostis.

Disease progress at numerous golfcourses also was monitored between1999 and 2001 (map above and Table 2).In addition, a mail survey intended tocollect information regarding the soilcharacteristics, cultivar(s) used, and anychemical or fertilizer applications thatmay have influenced BDS incidenceand severity was sent to 21 golf courses.A timeline ofBDS incidence andseverity was developed based on theinitial outbreak of BDS and the severityof the disease in consecutive years.

BIOLOGY OF THE PATHOGENWinter-dormant creeping bentgrassfield samples showing symptoms of

BDS were incubated at temperaturesranging from 59°F to 86°F (15°C to30°C). Between 12 and 28 days ofincubation, reactivation ofBDS symp-toms occurred at temperatures;::: 68°F(20°C), but the greatest expansion inBDS patch diameter occurred at 77°F(25°C) and 86°F (30°C). The optimumtemperatures for growth of hyphaeamong ten O. agrostis isolates rangedfrom 77°F to 86°F (25°C to 30°C), andgrowth was suppressed at 95°F (35°C).

Pseudothecia of O. agrostis was pro-duced in the lab on a mixture ofsterilized tall fescue seed and wheatbran. Pseudothecia developed underconstant fluorescent light at 55°F to82°F (13°C to 28°C), but no pseudo-the cia developed in darkness at anytemperature. Pseudothecia developed inas few as four days, and mature asco-spores were forcefully discharged orexuded en masse in the presence ofwater after a week of incubation.

Ascospores (fungal spores producedin pseudothecia) germination wasrapid. Ascospores incubated at 86°F(30°C) germinated in as little as twohours. Germination during the firstfour hours of incubation was enhancedby both light and the presence of bent-grass leaves or roots. Mter 18 hours ofincubation, however, there were fewdifferences in the percentage of asco-spores germinated, regardless of lighttreatment or presence of plant tissue.Ascospores were observed to eitherdirectly penetrate leaves and stems, or toenter leaves through open stomates (i.e.,pores in the leaves of all higher plantsused for gas exchange and evaporativecooling). Hence, O. agrostis can rapidlyproduce enormous numbers of sporesthat are capable of infecting new plantswithin a few hours.

CULTIVAR EVALUATIONData from this study revealed thatO. agrostis attacks all of the commonAgrostis species and cultivars grown ongolf courses. Individual cultivars withina species showed varying levels ofsusceptibility. The velvet bentgrass

JANUARY-FEBRUARY 2003 21

Table 2Location, cultivar, date samples were received, and date of planting of 19 creeping bentgrass and

hybrid bermudagrass greens confirmed to be infected by Ophiosphaerella agrostis, 1998-2001.

Date

SampleGolf Course/State Cultivar(s )/Blend Received Planted"P. B.Dye G.C., MD Penn G-2 Aug. 1998 Apr.-June 1998 (se)ZLowe's Island Club,VAv Pennlinks Sept. 1998 Autumn 1997 (se)Beechtree G.C., MD L-93+Crenshaw Oct. 1998 Aug.-Sept. 1997 (se)Ocean City G. &Y:C.,MD Penncross Oct. 1998 June 1997 (se)Hayfields C.C., MD L-93+Crenshaw Oct. 1998 Autumn 1997 (se)Sand Ridge C.C.,OH L-93 Oct. 1998 Summer 1997 (se)Marlton G.C., MD L-93+Crenshaw Oct. 1998 Oct. 1997 (se)Hampshire Greens G.C., MD Providence Nov. 1998 Oct. 1996 (se)Skokie G.C., ILw,x SRII19 Dec. 1998 Sept. 1996 (se)Hartefeld National G.C., PA Crenshaw+Southshore Dec. 1998 Sept.-Nov. 1994 (se)Texas A&M University,TX Champion June 1999 Summer 1997 (sp)Trenton C.C., NJ L-93 June 1999 Nov. 1998 (sd)Scotch Meadows G.C., NCw'Y Penncross June 1999 Aug. 1998 (se)Persimmon Woods G.C., MO Penn G-2 July 1999 Sept. 1997 (se)Rutgers University, NJ L-93 July 1999 Nov. 1998 (se)River Bend G.C., MA L-93 July 1999 June 1997 (se)Bulle Rock G.C., MD L-93 Aug. 1999 June 1997 (se)The Bridges G.C., PA Penncross Aug. 1999 Summer 1994 (se)Honeybrook G.C., PA L-93 Nov. 1999 Apr.-June 1999 (se)Inniscrone C.C., PA L-93+SR1020+Providence Mar.2000 Autumn 1997 (se)Orchard Creek G.C., NY L-93 Aug. 2000 Sept. 1998 (se)Red Hawk G.C., MI Providence Sept. 2000 Autumn 1998 (se)Atlantic City C.C., NJ PennA-4 Sept. 2000 Sept. 1999 (se)Glen View Club, ILwx SR1119+L-93+Providence Dec. 2000 Sept. 1999 (se)Olympia Fields C.C., ILw,x L-93 Dec. 2000 Sept. 1999 (se)KellyPlantation G.C., FL TifDwarf Apr. 2001 July-Sept. 1998 (sp)Mountain Branch G.C., MD L-93 July 2001 Sept. 2000 (se)Blue Mash G.C., MD PennA-4 Aug. 2001 Sept. 2000 (se)

v Disease also found on Penncross tees seeded in 1997 and 1998.W Area fumigated with methyl bromide prior to seeding.x Isolated by Dr. Randy Kane, University of Illinois.YIsolated by Dr. Henry Wetzel, North Carolina State University.ZSeeded (se), sodded (sd), sprigged (sp).

cultivars SR 7200 and Bavaria generallywere the most and least susceptiblecultivars, respectively. Bardot colonialbentgrass was highly susceptible toBDS, but it exhibited the greatestamount of recovery prior to winter.

The creeping bentgrass cultivarsexhibited varying levels of susceptibilityand recovery. Among the creepingbentgrass cultivars, L-93 had thegreatest number of infection centersduring the period of highest diseasepressure (September 6,2000), but thenumber of infection centers was not

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

significandy different from many othercreeping bentgrass cultivars, includingPennA-l,A-4, G-l, G-6, Imperial,ABT-CRB-l, and Providence. Penn-links, Penncross, and Crenshaw hadBDS levels that were not significandydifferent from the least susceptible culti-var (Bavaria) on September 6,2000, andgenerally were the least susceptiblecreeping bentgrass cultivars over thecourse of the study.

Recovery ofBDS patches was slowand did not begin to occur until afterSeptember 6,2000. Once bentgrass

growth decreased in late autumn, litderecovery occurred and spots remainedevident until growth resumed in latespring. Recovery was most apparentduring late spring and early summer.Recovery of all cultivars from BDSprobably was enhanced by fertilizerapplications in September andNovember. In 2001, BDS levels wereconsiderably less and new infectionswere minimal. Most infection centersfrom 2000 continued to recover, butnew disease activity was observed inseveral previously infected spots

may reduce the defense capabilities ofbentgras~ plants.

Bentgrass dead spot activity wasobserved as early as May but generallywas most active during the summer andearly autumn months. Recovery ofBDS patches was slo~ and active spotsoften remained evident until the firsthard frost. Soil pH at construction andduring periods of disease activityranged from 4.9 to 7.8.Various nitrogen(N) sources were applied at differentgolf courses throughout the year.Although no association between anysingle N source and disease outbreakcould be made, applying small amountsof water-soluble N (0.1 to 0.125 lb. Nper 1,000 sq. ft.) with each fungicideapplication may help to reduce BDSseverity and speed bentgrass recovery.

between June and September, 2001. Allbentgrass cultivars fully recovered byNovember, 2001.

In 2002, the disease reappeared in Julyfollowing a prolonged period of heatstress. Disease levels were moderatelysevere and BDS infection centers weregreatest in ABT-CRB-1, BAR AS8US3, Century, L-93, PennA-1, PennG-6, and SR1119. The reason fordecreased BDS activity by 2001 isunknown. A similar decline occurs withtake-all patch (Gaeumannomyces graminisvar. avenae) in Agrostis turf in response toa buildup of bacterial antagonists (6,7).Decline in BDS activity may be attrib-uted to the buildup of antagonistic soilmicroorganisms, maturation of the turf,variable environmental conditions, orthe cultural practices and the chemicalsemployed. Data collection in 2002,however, revealed that the disease canreactivate in older turf under conditionsof high temperature stress.

FIELD OBSERVATIONSAND SURVEY RESULTSBentgrass dead spot was found only onnewly constructed greens or whereolder greens were fumigated withmethyl bromide. The disease generallydeveloped between one and two yearsfollowing bentgrass establishment.However, outbreaks also were observedin creeping bentgrass greens that wereless than one year old and as old as sixyears. With few exceptions, BDS wasmost severe during the first or secondyear of symptom expression anddeclined as the greens aged. The declinephase generally lasted anywhere fromone to three years after the first year ofdisease expression, with the number ofinfection centers per green normallydecreasing in subsequent years.

All newly constructed greens affectedby BDS consisted of at least 80% sandas the primary soil medium. In addition,two older golf courses were renovatedusing methyl bromide but had a sand-based medium from several years of top-dressing. Although BDS was observedprimarily on the putting surfaces,

occasionally it was found on sand-basedbentgrass collars and tees, indicatingthat O. agrostis can attack creepingbentgrass maintained at higher mowingheights. Bentgrass dead spot was notfound in fairways or other sites wherebentgrass turf was grown on native soil.

Active BDS infection centersgenerally appeared in areas with full sunand good air circulation, and diseaseseverity varied from a few spots toseveral hundred per green. In addition,O. agrostis infection centers occurredpredominantly along ridges and onmounds and south-facing slopes ofgreens. These areas are particularlyprone to higher soil temperatures andoften are the first to exhibit droughtsymptoms. These conditions generallyresult in higher levels of plant stress and

During early stagesof disease develop-ment, the spots arereddish brown orcopper colored andmimic ball-markinjury. Except insevere cases, thepatches generallydo not coalesce,but recovery ofbentgrass dead spotpatches is slow andspots may not fullyrecover prior towinter.

During the earlystage of bentgrassdead spot develop-ment, new spotsappear reddishbrown or bronze.As diseased spotsincrease indiameter, theperiphery of activespots maintains areddish-brownappearance, whiledead tissue in thecenter appears tan.

J A N U A R Y - FE B R U A R Y 2003 23

According to Wetzel (9), weekly appli-cations of urea in conjunction with aneffective fungicide reduced BDSseverity. When applied weekly, however,urea alone did not significantly reduceBDS severity when compared to theuntreated control (9). Field fungicideevaluation trials reported by Wetzel (9)and Towers (8) showed that propicona-zole (Banner), chlorothalonil (Daconil),thiophanate methyl (Cleary's 3336),tludioxonil (Medallion), and iprodione(Chipco 26GT) effectively controlledBDS.

Unlike otherturfgrass pathogens

within the genusOphiosphaerella,

O. agrostiscommonly

produces f1ask-shaped fruiting

bodies known aspseudothecia on

necrotic leaf,sheath, and

stolon tissue.

Bentgrass dead spot can be foundin creeping bentgrass as far north asMichigan, as far west as Missouri, andalong the eastern seaboard of theUnited States from Massachusetts toNorth Carolina. In addition, O. agrostiswas found in Texas and Florida, causingdead spots in hybrid bermudagrass(Cynodon dactylon x C. transvaalensis)greens that had been overseeded withroughstalk bluegrass (Poa trivialis). Theoccurrence of O. agrostis infection ofbermudagrass in Texas subsequently wasreported by Krausz et al. (5). The role ofPoa trivia lis in the introduction of thepathogen and spread of the disease isunknown.

IN SUMMARYSurvey reports an~ cultivar evaluationtrials revealed that creeping, colonial,and velvet bentgrasses are susceptible to

24 GREEN SECTION RECORD

BDS. Of the 28 different golf coursesfrom which O. agrostis was isolated,however, 14 had grown L-93 in mono-stands or in blends. It is worth notingthat only a single isolate was used in thisstudy, and that varying races of thepathogen may exist in nature.Variationamong O. agrostis isolates could result invarying levels of disease severity amongbentgrass cultivars.

The fungus rapidly produces fruitingbodies in the absence of fungicide use,and the pathogen is rapidly dispersed byascospores. Under suitable conditions,

ascospores can germinate in as little astwo hours. The disease was most com-monly found on greens within twoyears following the seeding of newgreens or on older greens that had beenfumigated with methyl bromide.

Field observations confirm that thedisease normally declines dramaticallywithin one to three years. The oldestgreens where BDS was found weresix years old. However, disease mayreappear during periods of prolongedheat stress. Thus far, BDS appears to berestricted to sand-based greens, collars,and tees, and it has not been found inbentgrass or bermudagrass grown onnative soil.

Results of the survey and otherobservations confirmed that the diseaseis most prevalent in July and August, butit may appear in May and can remainactive in bentgrass as late as December.

In a bermudagrass green in Florida,however, the disease appeared as early asMarch.

ACKNOWLEDGMENTSWe thank the United States Golf Associationfor providing fmancial support for this study,R. Kane and H. Wetzel for providing isolates,and all of the golf course superintendents whocontributed information.

LITERATURE CITED1. Camara, M.P.S., N. R. O'Neill, P. van Berkum,

P. H. Dernoeden, and M. E. Palm. 2000.Ophiosphaerella agrostis sp. noVoand its relation-ship to other species of Ophiosphaerella.Mycologia 92:317-325.

2. Dernoeden, P. H., N. R. O'Neill, M.P.S.Camara, andY. Feng. 1999.A new disease ofAgrostis palustris incited by an undescribedspecies of Ophiosphaerella. Plant Disease 83:397.

3. Krausz,]. P., R. H.White,W Foerster, N.A.Tisserat, and P. H. Dernoeden. 2001. Bermuda-grass dead spot: A new disease of bermuda grasscaused by Ophiosphaerella agrostis. Plant Disease85:1286.

4. Kaminski,]. E., P. H. Dernoeden, N. R.O'Neill, and B. Momen. 2002. Reactivation ofbentgrass dead spot and growth, pseudo the ciaproduction and ascospore germination ofOphiosphaerella agrostis. Plant Disease 86:(InPress).

5. Kaminski,]. E., and P. H. Dernoeden. 2002.Geographic distribution, cultivar susceptibility,and field observations on bentgrass dead spot.Plant Disease 86:(In Press).

6. Smiley, R.W, P. H. Dernoeden, and B. B.Clarke. 1992. Diseases of roots. Pages 57-58.In: Compendium of Turfgrass Diseases. TheAmerican Phytopathological Society Press,St. Paul, Minn.

7. Smith,]. D., NJackson, and A. R.Woolhouse.1989. Fungal Diseases of Amenity Turf Grasses.E. & F. N. Spon, New York, NY.

8.Towers, G.W, P. R. Majumdar,E. N.Weibel,C. L. Frasier,]. NVaiciunas, M. Peacos, andB. Clarke. 2000. Evaluation of chemical andbiological fungicides for the control of bent-grass dead spot in creeping bentgrass. 2000Rutgers Turfgrass Proceedings 32:211-215.

9. Wetzel, H. C. 2000. Evaluation of fungicidesand urea for the control of bent grass dead spotin an "L-93" putting green in Raleigh, NC.,1999. Fungicide and Nematicide Tests 55:510.

JOHN E. KAMINSKI is a graduate researchassistant, and PETER H. DERNOEDEN isa prifessor in the Department of NaturalResource Sciences and LAndscape Archi-tecture at the University of Maryland.