defining the nature of creeping bentgrass root diseases defining the nature of creeping bentgrass...

Defining the Nature of CreepingBentgrass Root DiseasesResearch directed toward accurate diagnosis andmanagement of putting green diseases.BY LANE P. TREDWAY AND J A M E S P. KERNS

any golf course superinten-dents in the southeasternUnited States have recently

experienced unusual disease problemsin creeping bentgrass putting greens.The problems have been mainly limitedto newly constructed greens, builtwithin the past six years. Disease symp-toms typically appear during the latespring and summer in circular patchesranging from three inches to several feetin diameter. In these patches, the turfinitially exhibits signs of wilt or nutrientdeficiency, but the foliage continues todecline and turns yellow to orange incolor. Examination of affected plantsduring the summer reveals a tan, brown,or black rotting of the crown and roots.These characteristics, combined withthe young age of affected greens, wereconsistent with take-all patch, whichwas the diagnosis provided by severalpathologists across the country.

Take-all patch has historically beenlimited to the northern United States,but it also occurs in mountainous areasof the western Carolinas and northGeorgia. Take-all patch is not known tooccur at lower elevations in the South-east. We examined the problem moreclosely and found that the take-all patchpathogen, Gauemannomyces graminis, var.avenae, was not present in these regions.This led to the conclusion that anundescribed disease was responsible. Infact, we now know that there are atleast two previously unknown diseasesoccurring on creeping bentgrass in thesoutheastern United States.

Summer patch, caused by Magnaporthepoae, is one of the new creeping bent-

grass diseases discovered in NorthCarolina.4 This disease is a well-knownproblem in bluegrass species across theUnited States. In 1993, M. L. Elliottidentified M. poae as a pathogen ofcreeping bentgrass in Orlando andPalm Beach, Fla.1 However, summerpatch was not known to be a problemon creeping bentgrass within its normalgrowing regions. Thus far, summerpatch appears to be very isolated inNorth Carolina and has only beenobserved in areas with high soil pH(>7.0). Based on our observations,reduction of soil pH to 6.5 or less is avery effective means for managementof summer patch in creeping bentgrass.

Another undescribed disease hasbeen more widely distributed in thesoutheastern United States. This diseasehas been observed as early as fourmonths after seeding of newly con-structed greens and has been observedon most of the new-generation creep-ing bentgrass varieties. In contrast tosummer patch, soil pH does not appearto influence this disease, as it has been

Typical disease

symptoms observed

during the summer

in newly constructed

creeping bentgrass

putting greens in thesoutheastern United

States.

observed in soils with pH ranging from4 to more than 7.

Unfortunately, this particular diseasehas been very difficult to characterize.In fact, we have been unable to con-sistently isolate any pathogens from theaffected turf during the summer months,when the symptoms are most common.The tan to light brown rotting ofcrown and root tissues appears to becaused by secondary pathogens, such asCurvularia spp., that are attacking thealready weakened plants.

A major breakthrough occurred inNovember 2003 and March 2004 whenmild symptoms of this unknown diseasereoccurred in several locations, inducedby unusually warm and dry weather.At that time, several unusual symptomswere observed in the actively growingbentgrass roots: dead root tips, lack ofroot hairs, and loose organization ofcortical tissues. A significant amount ofPythium hyphae was also observed inthe affected roots.

These symptoms are consistent witha disease called Pythium root dysfunc-

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Figure IDistribution of Pythium species isolated from roots exhibiting dysfunction symptoms in North Carolina and Virginia.9

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tion, which was described in 1985 as adisease of newly constructed bentgrassputting greens in Iowa.3 C. F. Hodgesconsistently isolated P. arrhenomenes andP. aristosporum from the roots of affectedbentgrass plants and demonstratedthe pathogenicity of these species ingrowth-chamber experiments. How-ever, the disease was not reproduced inthe field through inoculations, andcontrol practices were notinvestigated.

In North Carolina and Virginia,P. volutum and P torulosum were con-sistently isolated from roots exhibitingsymptoms of Pythium root dysfunctionin fall 2003 and spring 2004. Pythiumvolutum was dominant in every location,and P. torulosum was present in only halfof the locations. Previous research con-ducted by Feng and Dernoeden inMaryland demonstrated that P. volutumis very aggressive toward creeping bent-grass seedlings at cool temperatures(64°F), whereas P. torulosum is onlyweakly pathogenic.2

Based on these results, we suspectthat this more widely distributed diseaseis Pythium root dysfunction caused byP volutum. The majority of pathogengrowth and root damage appears tooccur during the fall and spring whencreeping bentgrass roots are activelygrowing. This activity may reduce theroots' ability to absorb water and nutri-ents. As a result, the bentgrass plants aremore susceptible to heat and droughtstress during the summer. The effect ofP volutum on creeping bentgrass rootfunction is currently being studied infield and growth-chamber experiments.Additional isolates from other south-eastern states reporting similar diseaseproblems also are being obtained forcomparison.

Based on our observations, culturalmanagement practices have a majorimpact on the development and severityof this disease. Any source of stress,including nitrogen and other nutrientdeficiencies, drought stress, and closemowing, appear to encourage the

disease. Regular hollow-tine aerificationand topdressing also appear to be im-portant tools for managing this disease.In fact, when symptoms of the diseaseappear, the most recent aerificationholes often remain completely healthy.Golf course superintendents whoexperience problems with this diseaseshould conduct a comprehensiveanalysis of their management programto identify potential sources of stress.Regular tissue testing for nutrient con-tent can be particularly helpful, andnematode populations also should bequantified in regions where theseparasites are common.

Considerable progress has been madein the development of effective fungi-cide programs for control of this sus-pected Pythium disease. Surprisingly, thestandard Pythium fungicides, such asmefanoxam (Subdue Maxx),propamo-carb (Banol),and fosetyl-Al (Signa-ture), have provided poor to moderatecontrol of the disease in our researchtrials. In 2003, we developed a curative

C i R E E N S E C T I O N R E C O R D

program that involved applications ofHeritage + 3336,Terrazole, and SubdueMaxx within the course of a week. Thisintensive program provided up to threeweeks of disease suppression in our trials.

In 2004, we applied the new Qolfungicide pyraclostrobin (Insignia20WG) for the first time and found itto be more effective than individualfungicides or the 2003 curative pro-gram. Insignia has provided up to 28days of curative control when appliedat 0.9 oz. per 1,000 sq. ft. and wateredin with % in. of water immediately afterapplication. The vast majority of golfcourse superintendents who haveapplied Insignia for control of this dis-ease have reported similar results. Golfcourse superintendents are stronglyencouraged to submit samples to adiagnostic lab before initiating this type

of control program so as to avoidunnecessary fungicide applications.

At this point, we still have far morequestions than answers related to thissuspected Pythium root disease. What isthe effect of rootzone infiltration rateand other construction practices? Whatis the source of pathogen inoculum innewly constructed greens? Why are thestandard Pythium fungicides not provid-ing adequate control? Why is pyraclos-trobin more effective than the otherQoI fungicides? What is the appropriatetiming for preventative fungicide appli-cations? Research is continuing atNorth Carolina State University toanswer these important questions andprovide golf course superintendentswith accurate methods for diagnosingand managing root diseases in creepingbentgrass.

LITERATURE CITED1. Elliott, M. L. 1993. Association of Magnaporthepoae with a patch disease of creeping bentgrass inFlorida. Plant Disease 77:429.

2. Feng,Y, and P. H. Dernoeden. 1999. Pythiumspecies associated with root dysfunction ofcreeping bentgrass in Maryland. Plant Disease83:516-520.

3. Hodges, C. F. 1985. Pythium-induced rootdysfunction of secondary roots of Agrostispalustris. Plant Disease 69:336-340.

4.Tredway L. P. 2005. First report of summerpatch of creeping bentgrass caused by Magna-porthe poae in North Carolina. Plant Disease89:204.

DR. LANE TREDWAY is an assistantprofessor and extension specialist in theDepartment of Plant Pathology at NorthCarolina State University;]AMES KERNSis a graduate research assistant and Ph.D.student in plant pathology at NorthCarolina State University.

Figure 2Curative control of suspected Pythium root dysfunction in A-1 creeping bentgrass at Myers Park Country Club in Charlotte, N.C.

Treatments were applied on July 20,2004, in 2 gal. H2O per 1,000 sq. ft., then watered in immediately with % in. of irrigation.Values repre-sent average of four replications. Insignia provided significantly better curative control using the Waller-Duncan K-ratio t-test (k= 100).

X 5-M 3

=• 3

2003 Curative Subdue MaxxProgram (I fl.oz.)

Terrazole Terrazole- Heritage Insignia(3.5 oz.) Subdue Program (0.4 oz.) (0.9 oz.)

Untreated

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