Strategies from the Fieldto Delay Fungal ResistanceTaking a holistic approach to diseasecontrol and managing fungal resistance. BY STANLEY ZONTEK

FUNGAL RESISTANCE! Thethought that your golf course mayone day develop a disease that is

resistant to the chemicals you know andrely upon causes most turf managersmore than a passing concern. It is a realworry, especially in the Transition Zoneareas of the country where the normalweather patterns each year includeextended periods of oppressive heatand humidity and are punctuated bythunderstorms. These are perfect con-ditions for fungal diseases to developand cause damage to turfgrasses. As ageneral rule, more disease problemsoccur in this region of the country thanthe more temperate northern regionsor in the South, where the moredisease-tolerant bermudagrasses aregrown. Suggestions on ways to controlturfgrass diseases without inducingfungal resistance are the subjects of thisarticle.

Currendy there is a debate amongturfgrass pathologists about whichfungicide use concept is the best. For-tunately, fungal resistance problems arenot yet rampant in the Mid-Adanticregion of the country, where diseasepressure is high and fungicide usage isheavier than in other regions. A fewcases of fungal resistance have occurred,associated primarily with gray leaf spotresistance to strobilurin fungicides, suchas Heritage, and with pythium blightresistance to Subdue. However, whenyou consider how many differentdiseases are a problem and how manyfungicide sprays are made during theyear, the superintendents in this regionof the country generally are doing avery good job of controlling disease

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The first line of defense for disease control is togrow a healthy stand of grass. Maintaining planthealth and improving the growing environmentare essential aspects of managing putting greenturf.

while managing, or at least delaying,fungal resistance problems.

Suggesting ways to manage diseaseproblems in a tough grass-growingregion of the country is the purpose ofthis article. Additionally, the practicesoudined in this paper are not a theo-retical approach to disease control. Theyare in routine use throughout the Mid-Adantic region and other areas of thecountry. Several turfgrass pathologistswere contacted in preparing this paper,and there was enthusiastic agreementthat a holistic approach to disease con-trol is the best method for managing orat least delaying fungal resistance tocurrendy available fungicides.

THE HOLISTIC APPROACHWhat is meant by a holistic approach?The definition of holism suggests a"functional relationship between parts

that make a whole." In this case, it couldinclude various management programsand techniques working together fordisease control and managing resistance.Call it what you like: Best ManagementPractices (BMPs), Integrated Pest Man-agement (IPM), or common sense andexperience, etc. Effective disease control,as it is commonly practiced in manyareas of the country, involves muchmore than simply spraying a fungicideevery 7-14 days. This holistic approachincludes:

PLANT HEALTHWeak, stressed grass is more prone todisease, and if disease occurs, unhealthygrass is slower to recover. Fungicides,even the best ones,just do not seem towork as effectively when grass is un-healthy. In my opinion, the cause formany a fungicide failure is unhealthygrass, rather than fungicide failure orfungal resistance. Simply put, healthygrass on putting greens is:• Free of Undue EnvironmentalStress. That is, a turf growing in agood grass-growing environment, freeof shade problems and enjoying goodair circulation and soil drainage.• Free of Undue Mechanical Stress.The grass should not be too heavilytopdressed, aggressively brushed,groomed, aerated, verticut, dethatched,or otherwise mechanically damagedduring periods of hot weather in thesummer. Spores of pathogens that causeanthracnose and other diseases enter thegrass plant more easily through woundscaused by mechanical damage.• Free of Mower Stress. Grass shouldnot be cut too closely during periods of

Streaking Pythium on a perennial ryegrass fairway will put fear into a golf course superintendent. A holistic approach to disease control is the best methodfor managing, or at least delaying, fungal resistance to currently available fungicides.

weather stress. This includes increasingmowing heights and not mowing grasswhen conditions are too wet. If freewater exists on the surface of a green,skip mowing that day, or mow later inthe day when the green is drier. Also,switch from grooved to solid rollers toreduce wounding and mower stress inthe summer.• Free of Chemical Stress. Inter-actions among growth regulators andfungicides can be an element of plantstress, especially during a hot andhumid summer. Heavy use of growthregulators also can slow recovery. Somepre emergence herbicides have beenlinked to chemically stressing the turf,too. In many situations, superintendentsin the Mid-Atlantic region avoid apply-ing pre emergence herbicides to greens(unless absolutely necessary) and relyupon postemergence control programsor the old standby, hand weeding. Thisis IPM using a EMP at its best!

These are some of the elements ofstress management over which a turf

manager has some control. Weakened,stressed grass ultimately can result indifficult-to-control disease problems,especially anthracnose and summerpatch, even though a sound fungicidespray program is in place. In fact, whenwe visit a golf course with a goodfungicide spray program and wheredisease problems are still occurring, welook beyond the chemicals beingapplied. We consider other stress factorsthat may be reducing the health of theturf and reducing the effectiveness ofthe chemical applications. Plant healthis the key factor in complementing afungicide spray program. Other healthfactors include:

FERTILITYPutting greens need fertilizer. As prac-ticed in the Mid-Atlantic region, mostgreens are fertilized on a light and fre-quent basis - not too much nitrogen,but not too little. This program involvesweekly to biweekly applications ofsoluble fertilizers at rates ranging from

0.10 to 0.20 lb. of actual nitrogen per1,000 sq. ft. per application. Micro-nutrients such as iron also are added.The goal is to keep the grass plantgreen, healthy, and growing during thesummer. In using this program, alwayscheck compatibilities between fertilizersand fungicides. Most soluble fertilizerscan be tankmixed with most fungicides,but read the label. In my opinion, theseapplications of soluble fertilizers improveturf health and make fungicides workbetter. Dr. Peter Landschoot, of PennState University, makes the point thatanthracnose is a low-nitrogen disease.Keep this in mind.

SPRAY VOLUMESRe-read the labels on the fungicidesyou use. I'll wager that you may not beusing enough water as a carrier whenfungicides are applied. If too 'little wateris used, fungicide sprays can becomeconcentrated in the upper canopy ofthe turf. The fungicide can be morerapidly mowed off than if the entire

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grass plant were to be thoroughlywetted with the spray solution. Thislack of water as a carrier can diminishcontrol and ultimately waste money.Also, penetrant fungicides enter thegrass plant and are translocated from thepoint of contact upward, and they seemto need this extra water.

How much water? While a contactfungicide alone may require only 1-2gallons of water per 1,000 sq. ft., mostfungicide combinations seem to need2-3 gallons per 1,000 sq. ft. as a mini-mum. For penetrants on fairways, 100gallons/acre is a standard recommenda-tion.Yes, this extra water may involvemore time to spray greens (or fairways),but higher spray volumes may improvecontrol, reduce the number of chemicalapplications, manage resistance, and savemoney.

Note: Fosethyl aluminum (Signatureand Prodigy) is the only true systemicfungicide - it can move upwards ordownwards in plants. These productsmay be the one exception to the sprayvolume guidelines.

NOZZLE TYPEThe nozzle you use should be of a typethat provides good coverage and thecorrect spray volume as per the fungi-cide label. All too often, one nozzleis used for fungicides and herbicides.This may not be the best procedure.Similarly, sprayers should be calibratedon a regular basis, and worn nozzles,regardless of their type, should be re-placed on a regular basis, but at leastonce per season. Increasingly, there is atrend to use flat fan or similar typenozzles to drive the fungicide spraydeeper into the grass canopy, usinghigher (but not too high) spray pressure.This seems to make good sense. Dr.Peter Dernoeden from the Universityof Maryland and Dr. Houston Couchof VPI, both state, "Flat fan typenozzles are preferred for disease controlapplications."

Here is the bottom line. All nozzletypes can be used to provide goodcoverage and disease control, although

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PHOTO BY JEFFREY GREGOS, UNIVERSITY OF WISCONSIN

This image compares nozzle spray patterns usingwater-sensitive paper. More yellow color repre-sents less coverage. Good coverage helps ensurebetter disease control. From top: XR Tee Jet.TwinJet.Turbo Tee Jet. Flood Jet, and RARaindrop.

some engineering is involved to achievethe proper sprayer configuration,including boom height, partial to 100percent overlap, proper nozzle angle,etc. There is an absolute need to havethe proper nozzle, calibration, pressure,and water to provide the best coverageand the best disease control.

FUNGICIDE SELECTIONWhy are fungicides finally mentionednear the end of this article? In reality, ifyou view disease control and the man-agement of resistance using a holisticapproach, fungicides are but one part ofthe disease control equation. Planthealth is first, followed by managingthose stress factors that can be con-trolled, followed by using the best spraytechniques to complement the mode ofaction of the fungicides being applied.

All too often, superintendents seemto use fungicides as a crutch. That is,they rely upon chemicals as their pri-mary means of disease control, and dis-count factors like maintaining planthealth and reducing stress. This is an all

too common mistake. When a fungicidespray does not seem to provide effectivecontrol, the common curse is that thefungicide is not working or that fungalresistance has occurred. Could it be thatthe grass is so weak that even the bestfungi-cides won't revive dying grass?

Fungicides are an important part ofan effective disease management pro-gram in the Mid-Atlantic region. Mostputting greens in this region are sprayedon a preventive basis beginning in thespring and continuing into the fall. Fora long list of reasons, most golf greens(except on new golf courses or thosewith rebuilt or regrassed greens) have acombination of bent grass and Foaannua. This mix of grass species is onecurse of older courses in the TransitionZone. There always seems to be somedisease that needs to be preventivelytreated, like anthracnose and dollar spot,leaf spots, pythium blight, brown patch,and those pesky root diseases likesummer patch and take-all patch. Thenthere are snow molds, yellow tuft, ete.See what I mean? There always is adisease problem to be managed. Whenfungicides are applied, the followingguidelines are offered.

TANK-MIX ANDROTATE CHEMISTRIESThis technique is first choice for manysuperintendents in the Mid-Atlanticregion. They tank-mix a contact fungi-cide with a penetrant fungicide. For thenext spray, they again include a contactfungicide with another penetrant thathas a different chemistry and mode ofaction. Part of this spray rotation in-cludes our industry's only true systemicfungicide, fosethyl-aluminum (Signatureor Prodigy), tank-mixed with a contactfungicide. This is a continual processthroughout the spray season, i.e., alwaysrotating between penetrant fungicides(acropetal or local), while normallyincluding a contact fungicide in eachspray mixture. There is now researchsupport for this technique.

In a disease epidemiology modeldeveloped by Dr. Paul Vincellli of the

University of Kentucky, research sug-gests that "fungal resistance was delayedbest with a tank-mix of contact andsystemic fungicides or contact andpenetrant fungicides."

Yes, this program is more expensive,but it seems to work best. This modelalso is supported by what superinten-

dents and other plant pathologists in theMid-Atlantic region have experienced.In an article of this type, it is difficultto recommend specific products forspecific diseases. Contact your statecooperative extension specialists oryour regional USGA agronomists foranswers to disease control questions youmay have. In the final analysis, tank-mixing of fungicides along with solublenitrogen (when compatible) seems tomake a wonderful fungicide spray blendto promote plant health, control disease,and manage (delay) fungal resistance.

ALTERNATE CHEMISTRIESThis seems to be a second choiceapproach to disease control, but it stillis an effective program. An individualfungicide chemistry is applied, thenalternated to another chemistry for thenext spray.This approach seems to workbest in a preventive spray program. Theaddition of soluble fertilizers (whencompatible) also works well using thisprogram.

Note: If a curative fungicide applica-tion is needed with either approach,

spray intervals should be compressed,rates increased from preventive to cura-tive rates, and a tank-mix programusing a contact with a penetrant fungi-cide should be scheduled until diseasecontrol has been achieved.

YOUR EXPERIENCEThis choice should never be discounted.Individual golf course superintendentsknow their courses better than anyone.If you are satisfied with the results fromyour existing green management and

Reductions in mowing heightto achieve green speed haveagronomic consequences.Superintendent Rhys Arthurfrom Indian Spring CountryClub (Silver Springs. Md.) hasa sign that says it all.

fungicide spray program, why change asuccessful program for the sake ofchange?You could be one of the fortu-nate courses that has yet to experiencedifficult-to-control disease problems ongreens. In the long run, however, one ofthe previous choices most likely will bemore effective in delaying fungalresistance.

LUCKOne last aspect of resistance manage-ment and disease control should bementioned. It is luck, both good andbad.Yes, luck enters into this issue.Here's why. All fungi are not exactly thesame. There are individual races or bio-types of each pathogen, each of whichexhibits different levels of virulence.Golf courses don't necessarily share thesame pathogen biotypes. That is, onegolf course may have certain biotypesof the same disease while other golfcourses may have different biotypes.There is no way of knowing for surewhich race or biotypes you have onyour golf course. Dr. Peter Landschootof Penn State University, when referringto anthracnose, states, "There are benignraces of anthracnose and there areweapons-grade types."

Dr. Paul Vincelli, from the Universityof Kentucky, in studying gray leaf spotresistance to strobilurin fungicides,seems convinced that the resistancegene in the fungus pre-existed on thecourse before the first fungicide wasever applied! Perhaps this fact helpsto explain why one golf course mayexperience a disease problem and an-other golf course does not ... why onesuperintendent's fungicide spray pro-gram works and a similar program onanother course does not ... why onefungicide may provide an excellent levelof control on one golf course while ona neighboring course the same productdoes not work as well. The realizationthat not all of our pathogens are neces-sarily the same may help explain whyone course may be luckier or less luckyin its disease control efforts thananother course.

SUMMARYTo effectively control disease and delayfungal resistance, turf managers shouldtake a holistic approach to disease con-trol. Controlling disease while delayingfungal resistance involves much morethan using chemicals alone. Maintainingplant health and improving the growingenvironment are essential aspects ofmanaging putting green turf. Then,when chemicals are needed, theyshould be correctly applied. In the finalanalysis, which product to use and howto use it ultimately comes down to adecision that individual golf coursesuperintendents must make.

Our industry is light years away fromthe old days when the most commonlyused fungicide spray was a mix ofPMA(phenyl mercuric acetate) and Thiram,sprayed weekly, beginning in the springand continuing into the fall. Come tothink of it, wasn't this a tank-mix?

STANLEY J. ZONTEK,

directoroj the Mid-Atlantic Region} has beenwith the USGA GreenSection for 32 years.

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