FIELD SCIENCE

Fight springdead spot

Ifirst encountered spring deadspot (50S) in 2000 on a Tifway419 berrnudagraes fairway inVirginia Beach, VA while travelingwith a USGA agronomist. I remem-

ber the agony on the superintendent's face as wediscussed potential chemical control optionsand cultural practices to help reduce the damagefrom 50S the following spring. Finally the con-versation turned to complete renovation and wecontemplated a conversion to another speciessuch as creeping bentgrass, or a more resistantcultivar of bermudagrass. At the time, options forthis turf manager seemed bleak to say the least.Researchers understood less back then

about environmental and cultural practicesimpacting the life cycle of 50S, and there was nocommercially acceptable chemical control. Whilea 30-40% reduction in disease severity wasattainable, fungicide programs were costlybecause they typically required two or more applications. In addition,we understood less about the number. method, and timing of chemi-cal applications necessary to provide an effective fungicide programfor improved 50S control. Unfortunately, turt managers had very fewoptions other than getting through the season with some turf recov-ery and hope for the best the following year.Currently, more insight and information exists on how to fight 50S.

Scientists now understand more about the life cycle of the causalpathogens, cultural and environmental factors that influence 50Sdevelopment and breeding programs designed to select for moreresistant oermuoegrass cumvars. Also, chemical control options,including the timing and method of application of specific fungicides.are currently being assessed to develop more effective and improved

8 March 2006

By Gordon L. Kauffman, Ph.D.

fungicide programs to combat SDS. While my experiences with SOShave been primarily on golf courses, the disease can be problematicfor sports turf managers. Athletic field managers often have, or arelikely to deal with this disease if they are managing commonbermudagrass (Cynodon dactylon) and germuoagrass hybrids in thetransition zone, and primarily in the northern most range of bermuda-grass growth in the United States.

Symptoms and causal pathogenSDS is a particularly devastating perennial disease to Bermudagrassbecause the pathogen begins its colonization by infecting turtgressroots, stolons, and rhizomes. After visual diagnosis, control optionsare limited and likely too late. SOS infects bermudagrass of all ages,

www.greenmediaonline.com

FIELD SCIENCE

One difficulty in

interpreting SDS

fungicide trial data

is that test plots are

often not uniformly

infested. resulting in

plot rather than

treatment effects.

but most often occurs on established, 2-4year old, intensely managed turtgrassstands. SOS kills aermuoagrass down to thesoil surface while destroying roots, rhizomes,stolons, and shoots, leaving well defined,sunken, circular patches. Patches range insize from an inch up to a few feet in diame-ter and usually form as the bermuoagressbreaks winter dormancy, although the infec-tion likely occurs the previous fall If leftuntreated, the patches begin to coalesce anddevastate large turf areas.The causal pathogens of SDS are three

different root-infecting fungi calledOphiosphaerella herpotricha, O. korrae. andO. narman. These pathogens are classifiedas ectotrophic root-infecting fungi (ERIF)based upon the site of primary infections.Species of these fungi are soil borne andgrow over living turtgrass roots, rhizomes,and stolons similar to summer patch(Magnaporthe poae), which infects prim-arily bluegrasses, and take-all-patch(Gaeumannomyces gramtnts) of creepingbentgrass (Agrostis stoloniferous). Infectedroots and stolons typically become rottedand covered with dark brown or black hyphae.O. korrae also causes necrotic ring spot dis-ease of annual bluegrass (poa annual andKentucky bluegrass (pea pratensis).

10 March 2006

EnVironmental, cultural factorsSeveral key environmental factors increasethe chances of SDS infection and subse-quent colonization. SOS is most active whentemperatures and soil moisture favor fungalgrowth. Bermudagrass becomes most sus-ceptible when growth slows in the early falland spring during periods of cool, wet weath-er. Scientists believe, however, that much ofthe damage caused by SOS results from win-ter desiccation, making the initiation of falldormancy, severity of the winter, andbermudagrass cold hardiness important fac-tors for disease development. It appears thatduring the winter, SOS kills roots and crownsdirectly by infection, or indirectly by predis-posing the aermuoegrass to winter injury andsubsequent desiccation. bermudagrass cum-vars with increased cold hardiness tend toexhibit greater resistance to SOS.Cultural practices that promote increased

winter hardiness can minimize SOS damage.For example. excessive fall nitrogen applica-tions are not recommend in SOS proneareas. Avoid more than 4-5 lb. N/M/year, butmost importantly, discontinue nitrogen appli-cations at least six weeks before expectedbermudagrass dormancy. Additional culturalpractices used by turf managers to reducethe damage from SOS include routine corecultivation as an integral part of a thatchmanagement program, improving soildrainage and compaction, maintaining ade-quate potassium fertility, and the use of acid-ifying fertiiizers. Implementing these culturalsolutions can be an effective first step whendesigning an SOS management program.

Chemical controlControl of SOS with fungicides has beenspotty at best in the field and in control stud-ies at turtgrass research plots throughout theUnited States. In order to suppress diseasedevelopment, a systemic fungicide should beapplied in the fall, when the pathogen beginsto infect root tissue. The major factors influ-encing the control of SOS with fungicidesinclude the timing and dilution rate of theapplication. When targeting a soil bornepathogen like SDS, chemical applicationsshould be made in sufficient volumes of'water so that the fungicide can effectively

www.greenmediaonline.com

�mDSCIENCE

move through the turf canopy and positionedfor absorption by root and crown tissue. Onedifficulty in interpreting SDS fungicide trialdata is that test plots are often not uniform-ly infested, resulting in plot rather than treat-ment effects.Tredway and Butler (2003) studied both

the timing and application method on SDScontrol for two Tifway bermudagrass athleticfields. In general. they found that BannerMaxx (4 oz/M) and Rutngan lAS (6 oz/M)provided the best control of 5DS, improvingcontrol by 41% compared to the control.On one field, the method of applicationsignificantly affected 50S suppression.Applications in 5 or 10 gallons/M were moreeffective than applications in 2.5 gallons/M,ar 2.5 gallonsjM and watered in with one-quarter inch of water. Therefore. in this studyhigher dilution rates led to better controlof SDS. Syngenta's university sponsored re-search trials uncovered similar results.Increasing the spray dilution rate led to bet-ter control of dollar spot and brown patch onturfgrass maintained as a golf course fairway.In the same 50S study, trends were noted

regarding the most effective timing of fungi-cide applications on the control of SDS.Multiple applications were most effective anda single application made in August,September, or October was more effectivethan a one made in November. Fungicideapplications were most effective when soiltemperatures were between 60-80 degrees,prior to soil temperatures falling below 60degrees, when bermuoagrass root grovvthdeclines (Tredway and Butler, 2003). Basedon these and other field trial data, a fungicideprogram should be used as one componentto an integrated 50S management approachrather than as a silver bullet.Biocontrol options are worth mentioning as

an alternative approach to fighting SDS in thefuture. A bacterium was recently discoveredthat suppressed the growth of O. herpotrichain an Oklahoma State University laboratory.Applying bacterium as a soil drench hasthe potential for an effective component to anSOS management program. Research oe-signed to test these bacterium on field plotsstarted a couple of years ago, and the resultswill likely be available in the near future.

Achieving excellencerequires concentration

Too wet, too dry, too hard, too sott-keeping your field in top shape is otten hil ormiss. Stay entrack with Mar·CO's TargetAmendment Program lor ball diamondoptimization. Mar·Co has developed four

concentrated amendments that target the majorcauses ot poor infields. The following quick stepswill add me right amendment into your eXistingmix and create a sunaca mere right on the mark.Talk to your Mar-Co dealer lor details aboutimproving your ball diamond through the

Target Amendment Program.

1. M.A.P. it(sample & test)

2. Send it3. W",* it4. Play it

1-800-950-2555R.R.13 BRIGHT, ON NO.1 1BD

WWW.MARCDClAY.COMMARoCa....-....

Circle 115 on card or www.1II1ers.ims.ca{5905-115

12 March 2006

Breeding and the future researchAccording to turtgrass pathologists, bermuda-grasses with good winter hardiness will bet-ter resist 50S. If feasible, selecting a morecold resistant variety of Bermudagrass likeMidiawn, Midfield, Midiron, Mirage andSundevil is recommended. Some commoncold susceptible cultivars include Princess,Sonesta, Tifton 10, Sunturf, Tifway, Tifgreen,Tropica, and Oasis. Researchers are alsofocusing on specific pathogen-plant interac-tions in an attempt to breed for cultivarsmore directly resistant to the causalpathogens of 50S. The greatest limitation forturtgress breeders remains the lack of aquick screening procedure. Five to six yearsare generally needed to gather meaningfulresults. Therefore, controlled studies havebeen initiated in parallel with breeding todetermine specific plant genes that corte-spond to increased resistance to 50S.50S remains a devastating disease on

bermudagrass turf in transition zone andspecifically in the northernmost range ofbermudagrass adaptation because of thevariation in over-wintering weather conditionsand different levels of bermudagrass resist-ance to cold. These factors largely dictatethe extent of disease severity in the spring.Turf managers currently have more tools tofight the disease now compared to 5 yearsago, but we stiil have a long way to go.Similar to fighting other tough to control dis-eases that affect turtgresses. a multifaceted,integrated approach is essential. A programthat uses every option including speciesselection, advantageous cultural practices,careful monitoring of environmental condi-tions, and both chemical and biocontroloptions remains the current best defenseused to fight SDS.

References:Tredway, L.P. and E.L. Butler. 2003.Developing Effective Fungicide Programs forSpring Dead Spot Control. turtgrass Trends.Dec. 1, 2003.

Gordon Kauffman III, Ph.D., (gordon.kauff-man@syngenta.com),is a contracted field rep-

resentative with Syngenta Crop ProtectionInc., Greensboro. NC. •

www.greenmediaonline.com