Biological Control of Diseases on Golf Course Turf - USGA Green ...

A USGA-SPONSOREDRESEARCH PROJECT<strong>Biological</strong> <strong>Control</strong> <strong>of</strong> <strong>Diseases</strong> on Golf Course Turfby DR. ERIC B. NELSONCornell UniversityONE OF THE more excitingalternative strategies beingdeveloped for turfgrass diseasemanagement is the use <strong>of</strong> biologicalcontrols. Individual or mixtures <strong>of</strong>microorganisms are deployed to reducethe pathogens' activities or enhancethe disease tolerance <strong>of</strong> plants. Thisapproach to disease control has beenused successfully on an experimentaland commercial basis for the control <strong>of</strong>plant pathogens on several crop species,but only recently has it gained interestas an alternative pest managementstrategy for use on turf.The microbiology <strong>of</strong> disease-suppressivecomposts has not been extensivelystudied. A USGA-funded study entitled"Microbial Basis <strong>of</strong> Disease Suppressionin Composts Applied to GolfCourse Turf" is currently being conductedat Cornell University. The goal<strong>of</strong> this project is to understand the microbiology<strong>of</strong> composts in order to predictdisease-suppressive properties andassemble microbial antagonists usefulas inoculants or biological fungicidesfor turfgrass disease control.In addition to disease-causing microorganisms,turfgrass soils harbor avariety <strong>of</strong> non-pathogenic microorganismsthat actually improve plant health.These soil bacteria and fungi are responsiblefor increasing the availability<strong>of</strong> plant nutrients, producing substancesstimulatory to plant growth,and protecting plants against infectionfrom diseases. The practice <strong>of</strong> biologicalcontrol attempts to take advantage <strong>of</strong>these beneficial microbial attributes inorder to minimize damage from plantpathogens. <strong>Biological</strong> control may beachieved either through the application<strong>of</strong> introduced microbial antagonists orthrough the manipulation <strong>of</strong> nativeantagonists present in soils, composts,or on plant parts. In either case, the goalis to reduce or eliminate pathogenactivity by reducing pathogen inoculumin the soil, protecting plant surfacesfrom infection, or inducing naturaldefense mechanisms within the plant.The Use <strong>of</strong> Composts for<strong>Biological</strong> Disease <strong>Control</strong>Although few in-depth studies on thebiological control <strong>of</strong> turfgrass diseaseshave been conducted, promising resultshave been obtained using complex mixtures<strong>of</strong> microorganisms and individualantagonists as tools for managingfungal diseases <strong>of</strong> golf course turf (TableI). While individual organisms isolatedfrom many different environments canbe suitable for use as biological controlagents, compost-based organic fertilizersare perhaps the best sources <strong>of</strong>complex mixtures <strong>of</strong> antagonisticmicroorganisms.Composting has been defined as thebiological decomposition <strong>of</strong> organicconstituents in wastes under controlled605020Phase IPhase IITIMEconditions. Since composting reliesexclusively on microorganisms to decomposethe organic matter, the processhas biological, as well as physical,limitations. During composting, theenvironmental parameters (i.e., moisture,temperature, and aeration) mustbe stringently controlled. This is necessaryto maintain adequate rates <strong>of</strong>decomposition and to avoid the production<strong>of</strong> decomposition by-products thatmay be harmful to plant growth. Inorder to maintain proper temperatures,the composting mass must be largeenough to be self-insulating, but not solarge that compaction results in reducedair exchange. The composting massmust be moist enough to supportmicrobial activity, but not so moist thatair exchange is limited. The particle sizeColonizationByAntagonistsPhase IIII40IIII'j' .30IIIIIII/IFigure 1. During Phase I <strong>of</strong> the composting process, initial heating takes place and readilysoluble components are degraded. During Phase I/, cellulose and hemicellulose are degradedunder high temperature (thermophilic) conditions. This is accompanied by the release <strong>of</strong>water, carbon dioxide, ammonia and heat. Finally, during Phase IIL curing and stabilizationare accompanied by a drop in temperatures and increased humification <strong>of</strong> the material.Recolonization <strong>of</strong> the compost by mesophilic microorganisms occurs during Phase III.Included in these microbial communities are populations <strong>of</strong> antagonists.IIIIIIIZo~::)a..o a..~~ Zo~ ~Z

12 USGA GREEN SECTION RECORDii;, ".:P-: ,ii' ':,,I ~'eli49monal Spp.GaeW71anriomyces Spp.Bhialophora r;adicicolaComplex mixturesTJ(p~u,laphacorrhizalrichoderma spp.COInpl~x rnixtures:ii',,!-';,'i' ,'; ..••:.. ,m:;,; iF: di, '~n LOntario; CanadaN. CarolinaNew York, MarylandNew YorkOntario, CanadaSouth CarolinaNew YorkIllinois, OhioOhioColoradoNew YorkNew York, PennsylvaniaPennsylvaniaNew YorkNew YorkNew YorkN. CarolinaColoradoAustraliaAustraliaAustraliaOntario, CanadaMassach usettsNew YorkTurfgrassesCreeping BentgrassjAnnual BluegrassCreeping Bentgrass jAnnual BluegrassKentuckyPerennialKentuckyRyegrassCreeping BentgrassjAnnual BluegrassPerennialCreepingBluegrassRyegrassBluegrassBentgrassj<strong>of</strong> the material must be small enough toprovide proper insulation, but not sosmall that it limits air exchange.When all <strong>of</strong> the environmental andphysical conditions are optimized, compostingshould proceed through threedistinct phases (Figure 1) involving (1)a rapid rise in temperature, (2) a prolongedhigh-temperature decompositionphase, and (3) a curing phase wheretemperatures and decomposition ratedecrease. These three phases <strong>of</strong> decompositionare accompanied by successions<strong>of</strong> both mesophilic (moderatetemperature)and thermophilic (hightemperature)micr<strong>of</strong>lora. Each <strong>of</strong> thesemicrobial communities makes an importantcontribution to the nature <strong>of</strong> thecomposted material. Failure to maintainenvironmental conditions favorablefor adequate microbial activitycould jeopardize the quality <strong>of</strong> the finalproduct.In general, the longer the curingperiod, the more diverse the colonizingmesophilic micr<strong>of</strong>lora. These micr<strong>of</strong>loraare the most important in suppressingturfgrass diseases. At the presenttime, unfortunately, there is noreliable way to predict the diseasesuppressiveproperties <strong>of</strong> composts,since the nature <strong>of</strong> these colonizingmicrobial antagonists is left to chanceand determined largely by the micr<strong>of</strong>lorapresent at the composting site.Applications <strong>of</strong> composted materialcan suppress turfgrass diseases (Table2). Monthly applications <strong>of</strong> topdressingcontaining as little as 10 pounds <strong>of</strong>suppressive compost per 1,000 squarefeet were effective in suppressingdiseases such as dollar spot, brownpatch, Pythium root rot, Typhulablight, and red thread. Reductions inseverity <strong>of</strong> Pythium blight, summerpatch, and necrotic ringspot also havebeen observed in sites receiving periodicapplications <strong>of</strong> composts. Of particularbenefit is the impact <strong>of</strong> long-term compostapplications on root-rotting pathogensin soil. Populations <strong>of</strong> soil-bornePythium species are generally not suppressedfollowing traditional chemicalfungicide applications, but can bereduced on putting greens receivingcontinuous compost applications in theabsence <strong>of</strong> any chemical fungicideapplications. Also, heavy applications<strong>of</strong> compost (approximately 200 poundsper 1,000 square feet) to putting greensin late fall are effective not only insuppressing winter diseases, such asTyphula blight, but also in protectingputting surfaces from winter ice andfreezing damage.

(Left) Figure 2. Field research plotsimmediately after applying topdressingsamended with various composts andorganic fertilizers.<strong>Biological</strong> suppression <strong>of</strong> dol/ar spot on a creeping bentgrass / annual bluegrass putting green 32 days after application <strong>of</strong> selected compostsand organic fertilizers. (Left photo) The plot on the left was untreated, while the one on the right was treated with approximately 10poundsper 1,000 square feet <strong>of</strong> an organic fertilizer. (Right photo) The plot on the bottom was left untreated, while the one on the top was treatedwith a poultry litter/cow manure compost mixture at the rate <strong>of</strong> approximately 10pounds per 1,000 square feet.Composts prepared from differentstarting materials, as well as those atdifferent stages <strong>of</strong> decomposition, varyin the level <strong>of</strong> disease-suppression andin the spectrum <strong>of</strong> diseases that arecontrolled. This is primarily a result <strong>of</strong>the microbial variability amongdifferent composts and differences inthe quality <strong>of</strong> organic matter present ina compost at various stages <strong>of</strong> decomposition.Although microbial activityis necessary for disease-suppressiveproperties to be expressed in most composts,the specific nature <strong>of</strong> disease suppressivenessis, in general, unknown.In our research, several aspects <strong>of</strong> theecology <strong>of</strong> key compost-inhabitingantagonists are being investigated. Forexample, the ability <strong>of</strong> microbialantagonists to establish and survive inturfgrass ecosystems is necessary forbiological control to occur. The interactions<strong>of</strong> antagonists with other soilorganisms, and the soil or plant factorsaffecting optimum biological controlactivity, will be important in developingstrategies with compost-basedmaterials. In addition, these organismsmay serve as indicators <strong>of</strong> how long tocompost a material before it can becertified to be disease-suppressive.Research aimed at understanding thefate <strong>of</strong> antagonistic organisms in soilsand on plants following compostapplications will aid in understandingwhy composts fail at certain times andlocations. This research also shouldhelp predict the compatibility <strong>of</strong> compostsand their resident antagonistswith other pesticides and culturalpractices commonly used in turfmanagement.Individual microbial antagonistsfound in soils, composts, or in associationwith plants can, in many cases,suppress disease at levels typicallyachieved with composts or from use <strong>of</strong>fungicides (Figure 4). Due to theextremely close link between theirfunction and performance, however,one cannot readily predict antagonisticMARCH/APRIL 1992 13

Effect <strong>of</strong> various strains <strong>of</strong> Enterobacter cloacae and the fungicide metalaxyl on thesuppression <strong>of</strong>Pythium blight <strong>of</strong> perennial ryegrass in growth chamber experiments. <strong>Diseases</strong>everity was rated on a scale <strong>of</strong> 1 to 5, for which 1 equals no foliar blight and 5 equals 100percent foliar blight. A - Nontreated; B - Drenched with metalaxyl (750 pg a.i./ml);C - Treated with E. cloacae strain EcCT-50l; and D - Treated with E. cloacae strain E6.(From Nelson & Craft, 1991).behavior without an understanding <strong>of</strong>the microbial traits important inpathogen or disease suppression. It als<strong>of</strong>ollows that the performance <strong>of</strong>antagonists could be effectively enhancedif their function was clearlyunderstood.The traits necessary for an antagonistto suppress turfgrass disease are unknown;however, a number <strong>of</strong> traitsare currently being investigated. Forexample, these traits include the ability<strong>of</strong> antagonists to produce fungicidalcompounds or compounds that makenutrients unavailable to pathogens.Other traits include the ability <strong>of</strong>antagonists to parasitize pathogens,colonize plant parts, and compete withpathogens for resources in soil and onplants.The use <strong>of</strong> topdressing materialsamended with disease-suppressivecomposts or organic fertilizers hasreceived some acceptance by turfgrassmanagers as. an attractive diseasecontrolalternative. Many compostedmaterials and organic fertilizers arecommercially available from distributorsor municipal waste treatmentfacilities. Preliminary research hasshown that use <strong>of</strong> composts and organicfertilizers for turfgrass disease control iseconomically and technologicallypractical and, in some instances, canprovide reasonable levels <strong>of</strong> diseasecontrol. In the few cases that have beenexamined with some <strong>of</strong> these materials,a reduction in fungicide use has accompaniedthe adoption <strong>of</strong> this biologicalcontrol strategy.Before disease-suppressive compostsbecome widely accepted and used fordisease control, the principal problem<strong>of</strong> a compost not being consistentlysuppressive from year to year, batch tobatch, or from one site to the next mustbe solved. Turfgrass managers andcompost producers agree that the futuresuccess <strong>of</strong> these materials in commercialturfgrass management depends uponthe ability <strong>of</strong> producers to providematerials with predictable levels <strong>of</strong> diseasecontrol. Gross variation in diseasesuppressivequalities <strong>of</strong> composts cannotbe tolerated because end-users needto be assured that every batch <strong>of</strong>compost used specifically for diseasecontrol will work every time.Unfortunately, we do not yet knowhow to predict the suppressive activity<strong>of</strong> certain composts without actuallytesting them in field situations. Anumber <strong>of</strong> tests have been developed todetermine compost maturity and degree<strong>of</strong> stabilization for the purpose <strong>of</strong>reducing the variability in physical andchemical properties. Very little <strong>of</strong> theresearch, however, has been designed todirectly' assess microbiological aspects<strong>of</strong> maturity and disease suppressiveness.Currently, predictive tests basedon levels <strong>of</strong> microbial activity andorganic matter quality are beingexplored through this research projectas potential tools for predicting composts'disease-suppressive properties.Back to the Basics for Golf and the Environmentby GEORGE B. MANUELAgronomist, Mid-Continent Region, USGA Green SectionUOKING ahead into this decade<strong>of</strong> environmental concerns, it is adistinct possibility that superintendentsthroughout the country willexperience restrictions in the applicationor availability <strong>of</strong> pesticides. To preparefor these future reductions, thereis a need to search for alternatives tomake grasses healthier and less chemicallydependent. The successful superintendentin the 1990s will be one whois able to combine proven agronomicpractices <strong>of</strong> the past with some <strong>of</strong>14 USGA GREEN SECTION RECORDtoday's technology. A "back to basics"approach will help you meet theenvironmental challenges at yourdoorstep.Three <strong>of</strong> the most important factorsin maintaining healthy turf are propernutrition, reasonable cutting heights,and regular aeration. In order to preparea fertilization program, the soilfrom a portion <strong>of</strong> the greens, tees, andfairways should be tested annually. Forbest results, it is preferable to continuewith the same testing laboratory toachieve a consistent evaluation yearafter year.When test results are received, theyshould be examined closely and comparedto the previous year's analysis.Adjustments can then be made toprovide optimum growing conditionsfor the turf. In particular, potassiumand phosphorous levels should beclosely monitored. Soil potassium canbe depleted due to rapid uptake by theturf as well as its tendency to be leachedthrough the soil pr<strong>of</strong>ile. This results in