A USGA-SPONSORED RESEARCH PROJECT

Biological Control of Diseases on Golf Course Turfby DR. ERIC B. NELSONCornell University

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Antagonists

conditions. Since composting reliesexclusively on microorganisms to de-compose the organic matter, the processhas biological, as well as physical,limitations. During composting, theenvironmental parameters (i.e., mois-ture, temperature, and aeration) mustbe stringently controlled. This is neces-sary to maintain adequate rates ofdecomposition and to avoid the produc-tion of 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 size

TIME

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The Use of Composts forBiological Disease Control

Figure 1. During Phase I of 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 ofwater, carbon dioxide, ammonia and heat. Finally, during Phase IIL curing and stabilizationare accompanied by a drop in temperatures and increased humification of the material.Recolonization of the compost by mesophilic microorganisms occurs during Phase III.Included in these microbial communities are populations of antagonists.

Although few in-depth studies on thebiological control of turfgrass diseaseshave been conducted, promising resultshave been obtained using complex mix-tures of microorganisms and individualantagonists as tools for managingfungal diseases of golf course turf (TableI). While individual organisms isolatedfrom many different environments canbe suitable for use as biological controlagents, compost-based organic fer-tilizers are perhaps the best sources ofcomplex mixtures of antagonisticmicroorganisms.

Composting has been defined as thebiological decomposition of organicconstituents in wastes under controlled

ONE OF THE more excitingalternative strategies beingdeveloped for turfgrass disease

management is the use of biologicalcontrols. Individual or mixtures ofmicroorganisms are deployed to reducethe pathogens' activities or enhancethe disease tolerance of plants. Thisapproach to disease control has beenused successfully on an experimentaland commercial basis for the control ofplant pathogens on several crop species,but only recently has it gained interestas an alternative pest managementstrategy for use on turf.

The microbiology of disease-suppres-sive composts has not been extensivelystudied. A USGA-funded study entitled"Microbial Basis of Disease Suppres-sion in Composts Applied to GolfCourse Turf" is currently being con-ducted at Cornell University. The goalof this project is to understand the micro-biology of composts in order to pre-dict disease-suppressive properties andassemble microbial antagonists usefulas inoculants or biological fungicidesfor turfgrass disease control.

In addition to disease-causing micro-organisms, turfgrass soils harbor avariety of non-pathogenic microorgan-isms that actually improve plant health.These soil bacteria and fungi are re-sponsible for increasing the availabilityof plant nutrients, producing sub-stances stimulatory to plant growth,and protecting plants against infectionfrom diseases. The practice of biologicalcontrol attempts to take advantage ofthese beneficial microbial attributes inorder to minimize damage from plantpathogens. Biological control may beachieved either through the applicationof introduced microbial antagonists orthrough the manipulation of 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.

MARCH/APRIL 1992 11

of the material must be small enough toprovide proper insulation, but not sosmall that it limits air exchange.

When all of the environmental andphysical conditions are optimized, com-posting should proceed through threedistinct phases (Figure 1) involving (1)a rapid rise in temperature, (2) a pro-longed high-temperature decomposi-tion phase, and (3) a curing phase wheretemperatures and decomposition ratedecrease. These three phases of decom-position are accompanied by succes-sions of both mesophilic (moderate-temperature) and thermophilic (high-temperature) microflora. Each of thesemicrobial communities makes an im-portant contribution to the nature of thecomposted material. Failure to main-tain environmental conditions favor-able for adequate microbial activitycould jeopardize the quality of the finalproduct.

In general, the longer the curingperiod, the more diverse the colonizingmesophilic microflora. These micro-flora are the most important in sup-pressing turfgrass diseases. At the pres-ent time, unfortunately, there is noreliable way to predict the disease-suppressive properties of composts,since the nature of these colonizingmicrobial antagonists is left to chanceand determined largely by the micro-flora present at the composting site.

Applications of composted materialcan suppress turfgrass diseases (Table2). Monthly applications of topdressingcontaining as little as 10 pounds ofsuppressive compost per 1,000 squarefeet were effective in suppressingdiseases such as dollar spot, brownpatch, Pythium root rot, Typhulablight, and red thread. Reductions inseverity of Pythium blight, summerpatch, and necrotic ringspot also havebeen observed in sites receiving periodicapplications of composts. Of particularbenefit is the impact of long-term com-post applications on root-rotting patho-gens in soil. Populations of soil-bornePythium species are generally not sup-pressed following traditional chemicalfungicide applications, but can bereduced on putting greens receivingcontinuous compost applications in theabsence of any chemical fungicideapplications. Also, heavy applicationsof 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.

Perennial Ryegrass

Kentucky Bluegrass

Creeping BentgrassjAnnual Bluegrass

Perennial Ryegrass

Creeping BentgrassjAnnual Bluegrass

Creeping Bentgrass jAnnual Bluegrass

Kentucky Bluegrass

Turfgrasses

Creeping Bentgrassj

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12 USGA GREEN SECTION RECORD

(Left) Figure 2. Field research plotsimmediately after applying topdressingsamended with various composts andorganic fertilizers.

Biological suppression of dol/ar spot on a creeping bentgrass / annual bluegrass putting green 32 days after application of 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 of 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 of approximately 10pounds per 1,000square feet.

Composts prepared from differentstarting materials, as well as those atdifferent stages of decomposition, varyin the level of disease-suppression andin the spectrum of diseases that arecontrolled. This is primarily a result ofthe microbial variability amongdifferent composts and differences inthe quality of organic matter present ina compost at various stages of decom-position. Although microbial activityis necessary for disease-suppressiveproperties to be expressed in most com-posts, the specific nature of disease sup-pressiveness is, in general, unknown.

In our research, several aspects of theecology of key compost-inhabiting

antagonists are being investigated. Forexample, the ability of microbialantagonists to establish and survive inturfgrass ecosystems is necessary forbiological control to occur. The inter-actions of antagonists with other soilorganisms, and the soil or plant factorsaffecting optimum biological controlactivity, will be important in develop-ing strategies with compost-basedmaterials. In addition, these organismsmay serve as indicators of how long tocompost a material before it can becertified to be disease-suppressive.Research aimed at understanding thefate of antagonistic organisms in soilsand on plants following compost

applications will aid in understandingwhy composts fail at certain times andlocations. This research also shouldhelp predict the compatibility of com-posts and their resident antagonistswith other pesticides and culturalpractices commonly used in turfmanagement.

Individual microbial antagonistsfound in soils, composts, or in associ-ation with plants can, in many cases,suppress disease at levels typicallyachieved with composts or from use offungicides (Figure 4). Due to theextremely close link between theirfunction and performance, however,one cannot readily predict antagonistic

MARCH/APRIL 1992 13

Effect of various strains of Enterobacter cloacae and the fungicide metalaxyl on thesuppression ofPythium blight of perennial ryegrass in growth chamber experiments. Diseaseseverity was rated on a scale of 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 ofthe microbial traits important inpathogen or disease suppression. It alsofollows that the performance ofantagonists could be effectively en-hanced if their function was clearlyunderstood.

The traits necessary for an antagonistto suppress turfgrass disease are un-known; however, a number of traitsare currently being investigated. Forexample, these traits include the abilityof antagonists to produce fungicidalcompounds or compounds that makenutrients unavailable to pathogens.Other traits include the ability ofantagonists to parasitize pathogens,

colonize plant parts, and compete withpathogens for resources in soil and onplants.

The use of topdressing materialsamended with disease-suppressivecomposts or organic fertilizers hasreceived some acceptance by turfgrassmanagers as. an attractive disease-control alternative. Many compostedmaterials and organic fertilizers arecommercially available from distribu-tors or municipal waste treatmentfacilities. Preliminary research hasshown that use of composts and organicfertilizers for turfgrass disease control iseconomically and technologicallypractical and, in some instances, can

provide reasonable levels of diseasecontrol. In the few cases that have beenexamined with some of these materials,a reduction in fungicide use has accom-panied the adoption of this biologicalcontrol strategy.

Before disease-suppressive compostsbecome widely accepted and used fordisease control, the principal problemof 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 of these materials in commercialturfgrass management depends uponthe ability of producers to providematerials with predictable levels of dis-ease control. Gross variation in disease-suppressive qualities of composts can-not be tolerated because end-users needto be assured that every batch ofcompost used specifically for diseasecontrol will work every time.

Unfortunately, we do not yet knowhow to predict the suppressive activityof certain composts without actuallytesting them in field situations. Anumber of tests have been developed todetermine compost maturity and degreeof stabilization for the purpose ofreducing the variability in physical andchemical properties. Very little of theresearch, however, has been designed todirectly' assess microbiological aspectsof maturity and disease suppressive-ness. Currently, predictive tests basedon levels of microbial activity andorganic matter quality are beingexplored through this research projectas potential tools for predicting com-posts' disease-suppressive properties.

Back to the Basics for Golf and the Environmentby GEORGE B. MANUELAgronomist, Mid-Continent Region, USGA Green Section

UOKING ahead into this decadeof environmental concerns, it is a

distinct possibility that superin-tendents throughout the country willexperience restrictions in the applica-tion or availability of pesticides. To pre-pare for these future reductions, thereis a need to search for alternatives tomake grasses healthier and less chemi-cally dependent. The successful super-intendent in the 1990s will be one whois able to combine proven agronomicpractices of the past with some of

14 USGA GREEN SECTION RECORD

today's technology. A "back to basics"approach will help you meet theenvironmental challenges at yourdoorstep.

Three of the most important factorsin maintaining healthy turf are propernutrition, reasonable cutting heights,and regular aeration. In order to pre-pare a fertilization program, the soilfrom a portion of the greens, tees, andfairways should be tested annually. Forbest results, it is preferable to continuewith the same testing laboratory to

achieve a consistent evaluation yearafter year.

When test results are received, theyshould be examined closely and com-pared to 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 profile. This results in