S C I E N C E F O R T H E G O L F C O U R S E

d e d i c a t e d to e n r i c h i n g t h e e n v i r o n m e n t o f g o l f

Mixing fungicides controls disease on bentgrass greens Some tank mixes are more effective than others.

Paul Vincelli, Ph.D.

Fungicides with different modes of action may offer superior turfgrass dis­ease control when mixed, perhaps allowing lower rates of chemical use. Reduced fungicide use means reduced costs, reduced exposure of workers and golfers, and reduced risk of environ­mental contamination.

In addition, a tank mix may control more turfgrass diseases than one prod­uct alone. And tank mixes of fungicides can reduce the likelihood that resistant diseases will develop on the golf course.

Two common types of fungicides used in mixtures are:

• Contact fungicides, such as chlorothalonil

• Systemic "demethylization inhibi­tors" (DMIs)

DMI fungicides interfere with a chem­ical in fungi called ergosterol, which is an important component of cellular mem­branes. The DMI fungicides are mar­keted as Banner, Bayleton, Eagle, Rubigan and Sentinel. Chlorothalonil is the active ingredient in Daconil, Thalonil and other products.

DMI-chlorothalonil tank mixes are generally effective against several

^ ^ ^ ^ ^ ^ ^ ^ ^ Brown patch can be controlled more effectively with tank mixes of fungicides than B Q QQ w ' t n single-product spraying.

Golf Course Management • September 1997

continued from p. 49

important diseases of creeping bent-grass greens during summer, but thetank mixes described here control onlycertain foliar and crown diseases. Root-rot diseases such as take-all patch oncreeping bentgrass or summer patch onPoa annua, while controlled at higherrates of DMIs, will not be affected bylow rates of DMIs nor by a contactfungicide such as Daconil. Also, super-intendents will still need a separate pro-gram for Pythium control where condi-tions favor cottony blight.

Diseases controlledDollar spot

More money is spent to control dol-lar spot in the United States than anyother turfgrass disease (10). In centralKentucky, dollar spot often becomesvery aggressive from late spring throughmidsummer and again in autumn.

Sprayed at two-week intervals, DMI-chlorothalonil mixtures have providedexcellent control of dollar spot(5,11,12,13,15,18). This is not surpris-ing given the excellent activity of DMIfungicides against this disease.

Chlorothalonil alone often controlsdollar spot as well as the tank mix does.However, in some instances, preventivecontrol of dollar spot on a two-weekspray interval is superior with the DMI-chlorothalonil tank mix than withchlorothalonil alone, even when thechlorothalonil is used at the highlabeled rate (12,15).

Waiting four weeks between DMI-chlorothalonil applications is too longunder moderate-to-high disease pres-sure, even if the rate of the DMI isincreased. Also, stretching the sprayinterval to as long as four weeks mayincrease the risk of developing a DMI-resistant strain of Sclerotinia homoeo-carpa, the fungus that causes dollar spot.Such strains have been documented on anumber of golf courses (3,6).Anthracnose

In research on Penn cross creepmg

bentgrass with moderate-to-highanthracnose disease pressure, we havefound that DMI-chlorothalonil combi-nations applied biweekly have providedexcellent preventive control of anthrac-nose (12,14,16,19).

The combination provides moreconsistent control of anthracnose thandoes a labeled use of one of the prod-ucts by itself. Although generally effec-tive against anthracnose, chlorothalonilalone at labeled rates has not alwaysperformed as well against anthracnoseas has a DMI-chlorothalonil combina-tion (16,19).

Frequency of application is impor-tant. In one series of tests, we found thatpreventive applications of a Sentinel-Daconil mixture at three-week intervalsgave acceptable results against anthrac-nose. As with dollar spot, stretching thespray interval to four weeks sometimesresulted in some loss of anthracnosecontrol (16). Four weeks between treat-ments may open the door for selectionof DMI-resistant strains ofColletotrichum gramincola, the fungusthat causes anthracnose.

Preventive control of anthracnose isessential. It's difficult to promote recov-ery of creeping bentgrass from anthrac-nose during the heat of summer (21). Infact, curative control of anthracnoseisn't even an option on the labels forDaconil fungicide products. InKentucky, on anthracnose-threatenedgreens, we recommend beginning theDMI-chlorothalonil tank mix aroundMemorial Day; optimal starting dateslikely are different elsewhere.Brown patch

As a group, the DMI fungicides arenot highly effective against severebrown patch outbreaks; although some,such as Sentinel, are better than others.The contact fungicides chlorothaloniland iprodione (Chipco 26019 and otherproducts) are among the few that holdup well under most circumstances, atleast when used at high labeled ratesand frequent labeled intervals.

50 Golf Course Management • September 1997

When DMI fungicides and cWoro-thalonil have been tank mixedat low-to-moderate rates and appliedbiweekly, brown patch control variesfrom very good to excellent (9,11,16,19,20,22). However, less than completecontrol of brown patch was sometimesobtained with these mixtures using lowrates of both products under high dis-ease pressure (8,14,20).

As noted for dollar spot and anthrac-nose, the tank mix sometimes outper-forms the DMI alone against brownpatch, even when the DMI was used attwice the rate as in the tank mix (14).Stretching the spray interval of theDMI-chlorothalonil tank mix to threeto four weeks may result in some loss ofbrown patch control (2,4).

For sites with consistently highbrown patch pressure and low anthrac-nose pressure, the DMI-chlorothaloniltank mix at low rates should not berelied upon for the entire summer. Forthose sites, consider higher rates ofproducts with the strongest activityagainst brown patch, such aschlorothalonil, iprodione (Chipco26019 and other products), flutolanil(Prostar), or azoxystrobin (Heritage).Copper spot

Destructive outbreaks of copper spotoccasionally develop on creeping bent-grass greens during extended periods ofhot, humid weather. Biweekly tankmixes of several DMls withchlorothalonil at low rates of bothfungicide have provided complete con-trol during a destructive outbreak thatoccurred during sustained hot weather(unpublished data).

Growth regulationWhen applied at sufficiently high

levels, all DMI fungicides interfere with.the formation of the plant hormonegibberellic acid (7), much like some ofthe commercial turf grass growth regula-tors. Growth regulation is sometimesdesirable, of course, as it reduces theneed for mowing and maintains faster

putting speeds. Even so, concern ariseswhen unexpected growth regulationoccurs on greens that are subjected to avariety of stressful conditions. By tankmixing DMI fungicides at low-to-mod-erate rates, superintendents should .beable to maintain adequate levels offoliar disease control without causingany undesirable turf growth regulation.

AlgaeUse of DMI fungicides at moderate-

to- high rates has sometimes been asso-ciated with an increase in algae oncreeping bentgrass greens (1). DaconilUltrex is labeled for preventive controlof algal scums caused by certain blue-green algae, in combination with man-agement practices that promote surfacedrying of the green. A tank mix of aDMI fungicide at a low rate withDaconil Ultrex should minimize con-cern over algae blooms.

Disease managementPreventive applications of a DMI

plus chlorothalonil, with both fungi-cides at low-to-moderate rates, have a

COil I i 11 II C d

More fungicide is spent for control of dollar spot than for any other turfgrass disease.

Golf Course Management • September 1997 51

continued from p. 51

significant place in management ofsummertime foliar and crown diseaseson creeping bentgrass putting greens.Once diseases develop on greens duringsummer, conditions are often too stress-ful to promote rapid recovery. Thus,preventive use of DMI-chlorothaloniltank mixes is probably the best strategyfor many sites where high qualityis expected.

Rates, frequencies and restrictionswill be dictated by the products selectedand past disease problems. Recognizethat durations of disease control arevariable from one application to the

next. Important factors include diseasepressure, amount and frequency ofrainfall and irrigation and rate of turf-grass growth (which results in fungicideloss by mowing and exposure of new,untreated foliage).

Take care to monitor turf growthregulation effects when applying DMIfungicides to putting greens treatedwith plant growth regulators (PGRs).This is particularly important whenDMls are used at high labeled rates ongreens treated with "early GA synthesisinhibitors" such as flurprimidol(Cutless) and paclobutrazol (Scott'sTGR). Mild growth regulator effects

Disease control on a Penncross putting green in Lexington, Ky.,during 1994. Propiconazole alone(Banner) at a labeled rate and timing for anthracnose was not as effective as the combination (15,16).

Treatment and amount Spray No. dollar spot Percent plot Turfgrass qualityper 1,000 ft2 interval infection centers surface with rating on Aug. 2,

(weeks) per 16 sq. ft. plot anthracnose/ brown 1994. Scored 1-9,on July 18, 1994 patch complex* 9=excellent quality

on Aug.17,1994

Banner 1.1EC 0.5 fl oz + 2 Oa Oa 9.0 aDaconil 2787 4. 17F 4 fl oz 2

Banner 1.1EC 1.0 fl oz + 4 10 b 13b 7.7 bDaconil 2787 4. 17F 4 fl oz 4

Banner 1.1EC 1 fl oz 2 Oa 15 b 8.3 ab

Daconil 2787 4.17F 6 fl oz 2 7b Oa 7.3 b

Control (water spray) 2 59 c 78 c 5.5 c

Within each column, numbers followed by the same letter are not statistically different from each other.

*Turf damage was caused almost exclusively by anthracnose. No brown patch activitywas observed for eight weeks prior to this assessment date.

52 Golf Course Management • September 1997

include slightly darker and wider leafblades and shortening of internodes.When severely affected, creeping bent-grass can exhibit bronzing or bluish-yel-low discoloration.

Tests at the University of Kentuckyused 2.5 gallons per 1,000 square feetto ensure full coverage of leaf andcrown surfaces. Equivalent results maybe possible with lower spray rates.Some product labels specify how lowthe rate may be without sacrificing dis-ease control.

Formulations of several fungicideshave changed since we began testingtank mixes. For example, Banner 1.1EChas evolved to Banner Maxx. Anotherexample: Daconil 2787 has evolved toDaconil Ultrex, which as of this yearis available as WeatherStik formulation.Notwithstanding formulation changes,some generalizations in terms of ex-pected performance are possible.

Consider the following examples ofspecific tank mixes, with all rates refer-ring to amounts of product per thou-sand square feet:Banner-Daconil tank mixes

Probably the most thoroughly testedamong the DMI-contact mixes is a tankmix of propiconazole (Banner) andchlorothalonil (Daconil). A preventive,biweekly mixture of Banner Maxx at 0.5ounce and Daconil Ultrex at 1.8 to 3.6ounces can provide excellent protectionagainst dollar spot, anthracnose andcopper spot. In sites where anthracnoseis the primary target disease, a rate of2.75 ounces Daconil Ultrex would berecommended based on the label,although we often have achieved excel-lent control using the lower rate in thetank mix.

Control of brown patch should alsobe acceptable in most circumstances,especially if the higher rate of DaconilUltrex is used. Even higher, curativerates of Daconil may be required if an

outbreak develops in a site with unusu-ally high brown patch pressure .. Therates suggested should minimize brownpatch damage in most circumstances ifapplied biweekly and preventively.

It may be possible to stretch theapplication interval to as long as threeweeks in some instances, althoughbrown patch control can be expected toslip under moderate-to-high diseasepressure. Don't expect good results witha four-week spray interval. If brownpatch is active and the superintendentwishes to use a Banner product, thelabel requires application at a rategreater than 0.5 ounce and that it betank mixed with a contact fungicidesuch as chlorothalonil.Sentinel-Daconil tank mixes

Based on the tests published thus far,a three-week schedule of Sentinel(active ingredient cyproconazole) at 1/6

ounce Sentinel 40WG combined withDaconil Ultrex at 3.6 ounces may have aslight edge against brown patch over thebiweekly Banner- Daconil tank mix, andit should give about equal performanceagainst the other diseases mentioned.Don't expect this tank mix to hold upover a four-week interval, since theDaconil component is long gone bythen. Also, be aware of the restrictionthat no more than two applications ofSentinel 40WG at Yt, ounce be made ongreens within a 42-day period to avoidexcessive growth regulation. Copperspot control is likely to be quite accept-able, since both products are effectiveagainst this disease.Bayleton-Daconil tank mixes

Based on published tests withBayleton (active ingredient triadime-fon), biweekly applications of Bayleton25 at 0.5 ounce plus Daconil Ultrex at1.84 ounce have been excellent againstdollar spot and anthracnose, but only

continued

Golf Course Management. September 1997 53

Foliar infections of anthracnose (top) reduce turfgrass quality but have onlya temporary effect on the health of creeping bentgrass. Basal infections(center) can kill individual tillers, resulting in significant turf loss (bottom).

continued froll1 p. 53

moderate against brown patch. Higherrates of Daconil probably wouldenhance the level of brown patch con-trol for sites with high pressure fromthis disease. Copper spot control wasexcellent when a severe outbreak devel-oped in one test.Lynx-Daconil tank mixes

The DMI fungicide Lynx (activeingredient tebuconazole) is not yetlabeled. If and when this product doesreceive a federal label for turf, tests indi-cate it will provide excellent resultswhen tank mixed with chlorothalonil.Biweekly applications at relatively lowrates - Lynx 25DF at 0.5 ounce plusDaconil Ultrex at 1.84 ounces - pro-vided excellent control of brown patch,dollar spot, anthracnose and copperspot under very high disease pressure(18,19,20).Other products

Other fungicide tank mIxes havetheir own merits. For example, anumber of studies have looked at tankmixes of Eagle 40WP (active ingredi-ent mydobutanil) with mancozeb(the active ingredient in Fore andother products). This combinationgenerally has performed as well as aDMI-chlorothalonil tank mix, exceptunder high brown patch pressure.Here's another example: Our datawith a tank mix of iprodione andDMI fungicides are limited to a singletest, but we found it performed simi-larly to a DMI-chlorothalonil tankmix against dollar spot, brown patchand anthracnose (11).

Published results on tank mixingfenarimol (Rubigan products) ormydobutanil with chlorothalonil onputting greens have been limited. Thosestudies published in journals suggestthat either tank mix provides excellentefficacy against dollar spot but onlymoderate efficacy against brown patch.Additional field tests will help deter-mine how to best employ a DMI-chlorothalonil tank mix strategy using

54 Golf Course Management • September 1997

either fenarimol or myclobutanil.A fungicide with a new mode of

action, Heritage SOWG (active ingredi-ent azoxystrobin), has recently receiveda federal label for control of a numberof turfgrass diseases. This product willadd a new dimension to summertimedisease control on putting greens. Whileit does not control - and sometimescan increase - dollar spot (18), azoxy-strobin appears to be outstanding forcontrolling brown patch and anthrac-nose, two summertime diseases that areoften difficult to control consistentlywith any single product.

In testing to date, we have achievedexcellent results by applying a DMI-chlorothalonil tank mix, followed byHeritage two weeks later, then alternat-ing back to the DMI-chlorothalonil tankmix two weeks later, etc. This approachneeds further evaluation, but it mayoffer excellent control of a broad spec-trum of diseases as well as a possiblestrategy for reducing the risk of fungi-cide resistance to the systemic fungicidesused in that spray program .•

Literature cited1. Burpee, L.L., and S.L. Stephens. 1995. Effects

of DMI fungicides on summer and fall qualityof creeping bentgrass. University of GeorgiaTurfgrass Pathology Research Report. GeorgiaExp. Stn., Griffin, Ga.

2. Dernoeden, P.H., and M.A. Fidanza. 1995.Brown patch control with Prostar combina-tions, 1994. Fung. & Nemat. Tests 50:336.

3. Doney, J.e., and P. Vincelli. 1994. Control ofSclerotinia homoeocarpa with reduced sensi-tivity to DMI fungicides on two greens, 1993.Fung. & Nemat. Tests 49:327.

4. Gleason, M.L., N.e. Christians and J.P.Newton. 1994. Evaluation of fungicides forcontrol of brown patch in creeping bentgrass,1994. Fung. & Nemat. Tests 50:330.

5. Grogan, J.E., and D.H. Scott. 1995. Evaluationof fungicides for control of dollar spot increeping bentgrass, 1994. Fung. & Nemat.Tests 50:332.

6. Golembiewski, R.e., J.M. Vargas, A.L. Jonesand A.R. Detweiler. 1995. Detection ofdemethylization inhibitor (DMI) resistance inSclerotinia homoeocarpa populations. PlantDis. 79:491-493.

7. Koller, W. 1988. Sterol demethylizationinhibitors: mechanism of action and resis-tance. p. 79-88. In: e. Delp (ed.), FungicideResistance in North America. APS Press,St. Paul.

8. Rimelspach, J.W. 1996. Evaluation of fungi-cides for the control of brown patch, 1995.Fung. & Nemat. Tests 51:345-6.

9. Soika, M.D., and P.L. Sanders. 1995.Evaluation of fungicides for control of brownpatch, 1994. Fung. & Nemat. Tests 50:337.

10. Vargas, J.M., Jr. 1994. Management ofTurfgrass Diseases. 2nd ed. CRC Press, BocaRaton, Fla.

11. Vincelli, P.e., J.e. Doney and A.J. Powell.1992. Control of dollar spot and brown patchof creeping bentgrass, 1991. Fung. & Nemat.Tests 47:291.

12. Vincelli, P.e., J.e. Doney and A.J. Powell.1993. Control of dollar spot, brown patch,and anthracnose on creeping bentgrass, 1992.Fung. & Nemat. Tests 48:357.

13. Vincelli, P., J.e. Doney and A.J. Powell. 1994.Evaluation of fungicides for control of dollarspot, 1993. Fung. & Nemat. Tests 49:339.

14. Vincelli, P., J.e. Doney and A.J. Powell. 1994.Evaluation of fungicides for control of brownpatch and anthracnose/brown patch complex,1993. Fung. & Nemat. Tests 49:340.

15. Vincelli, P., J.e. Doney and A.J. Powell. 1995.Evaluation of fungicides for control of dollarspot, 1994. Fung. & Nemat. Tests 50:35.

16. Vincelli, P., J.e. Doney and A.J. Powell. 1995.Evaluation of fungicides for control ofanthracnose/brown patch complex, 1994.Fung. & Nemat. Tests 50:355.

17. Vincelli, P., J.e. Doney and A.J. Powell. 1995.Evaluation of fungicides for control of brownpatch, 1994. Fung. & Nemat. Tests 50:379.

18. Vincelli, P., J.e. Doney and A.J. Powell. 1996.Evaluation of fungicides for control of dollarspot, 1995. Fung. & Nemat. Tests 51:363.

19. Vincelli, P., J.e. Doney and A.J. Powell. 1996.Evaluation of fungicides for control of brownpatch and anthracnose, 1995. Fung. & Nemat.Tests 51:362.

20. Vincelli, P., J.e. Doney and A.J. Powell. 1996.Evaluation of fungicides for control of brownpatch, 1995. Fung. & Nemat. Tests 51: 365.

21. Vincelli, P., and J.e. Doney. 1997. Evaluationof fungicides for control of anthracnose, 1996.Fung. & Nemat. Tests. 52: (in press).

22. Vincelli, P., and J.e. Doney. 1997. Evaluationof fungicides for control of brown patch,1996. Fung. & Nemat. Tests. 52: (in press).

Paul Vincelli is a plant pathologist with theUniversity of Kentucky.

Golf Course Management. September 1997 55