Controlling moss in putting greens - GCSAA

This work was partly funded by the Oregon GCSA.RESEARCHS C I E N C E F O R T H E G O L F C O U R S Ed e d i c a t e d t o 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 fControlling mossin putting greensExtensive testing shows that some products control moss infestation tosome degree, but a dense stand of turf is still the best defense.Tom Cook, M.S.; Brian McDonald;and Kathy Merrifield, M.S.The virtual epidemic of moss onputting greens has prompted four years ofresearch on a wide range of chemicalcontrol strategies. Although this researchremains a work in progress, it hasrevealed a great deal about what worksand what doesn’t and about moss growthin putting greens. Here we outline currentcontrol strategies and point out areas offuture research.Biology and ecologyof putting green mossOf approximately 20 species of mossfound in association with turf in temperateclimates, Bryum argenteum, or silverythread moss, is the species most commonlyassociated with putting greens. Innature, B. argenteum is found from sealevel to timberline and from the Arctic toAntarctica. It is common in cold and temperateclimates but rare in tropical ones.Cosmopolitan and ubiquitous, it colonizesdisturbed, often dry sites and generally isconsidered a pioneering species. It isoften part of the early succession on sanddunes, bare rock and gravelly soil. Alongwith a small number of other mosses, it iswell adapted to human-altered environments,including sand-based puttinggreens and push-up greens that havebeen topdressed regularly with sand.Unlike many mosses, it grows well in bothwet, shady environments and hot, drysites in full sun.Like most bryophytes, B. argenteum isB ryum argenteum, the moss most commonly associated with putting gr e e n s ,d i fers in appearance from common lawn mosses.KEY pointsMore Info: www.gcsaa.orgBryum argenteum, or silvery threadmoss,has become a common peston putting greens.Products containing copper hydroxide,iron and fatty acids have allshown some ability to control mossin putting greens.A drastic change in cultural practicesmay be the best defense againstmoss infestations.not a vascular plant and has no roots. It isanchored by rhizoids, which resembleroots but do not appear to function inuptake of water or nutrients. Wi t h o u txylem and phloem, it has no means totranslocate foliar-absorbed nutrients. Likeother mosses associated with turf, B.argenteum reproduces via spores producedin distinctive capsules and by plantfragments likely spread during mowingand other cultural practices such as coring.To date, we have not observed sporecapsules on moss growing in putting turf.The current prevalence of moss inGCM

RESEARCHputting greens probably reflects recenttrends in putting green culture, includingextremely low mowing, minimal nitrogenf e r t i l i z e r, increased use of sand growingmediums, intense sand topdressing andloss of mercury fungicides, which werehighly toxic to moss. It occurs on bothbentgrass and Poa annua greens but isby far a bigger problem on sand-basedbentgrass greens. We have found significantpopulations on first-year greenson new golf courses. It often shows upfirst in weak areas such as ridges andmounds where grass is thin because ofscalping or drought stress. It aggressivelycolonizes low, wet areas andthrives on soil-based greens with shallowlayers of sand built up by topdressing.Research strategiesOur research, conducted at OregonState University, primarily concerns mossgrowing in creeping bentgrass greens,and the following results are from workdone entirely on Providence creepingbentgrass in sand-based growing mediumsand SR 7200 velvet bentgrass growingon soil and topdressed with sand. Todate we have concentrated on large-scalebroadcast treatments rather than spottreatments directed at localized infestations.Most of the chemical treatmentshave been applied during fall and winterwhen temperatures range from 40 to 65 Fand moisture from precipitation is common.Soil pH in the area is typically 5.5 to6.5, and salt levels are very low.Early screening trialsAfter unsuccessful attempts by superintendentsto try iron products at normalputting green rates, we screened a widerange of products by applying each at avariety of rates from low to very high.Products included in our experimentswere selected because reports in the literatureindicated that they controlled moss orthat they were being applied on puttinggreens in an attempt to control moss. Weeliminated products that caused turf damageand others that had no effect on themoss. The following products were testedand eliminated from consideration.Copper sulfate. Copper sulfate is notlabeled for moss control. In our tests, itRelative residual moss control in plots treated the previous winter with junction ( Copper Hydroxide + Mancozeb),No-Mas(fatty acid soas),daconil fungicide,and an untreated check plot.caused severe turf injury at rates necessaryfor moss kill. Caused root stunting int u r f .Copper soaps. Copper soaps are notlabeled for moss control. We found themto be highly effective moss killers but toxicto turf, even at moderate rates.Zinc sulfate. These products are notlabeled for moss control in putting greens,although some retail products are labeledfor moss control in lawns. A c c e p t a b l emoss control but caused significant turfinjury at marginally high rates.Daconil Zn and Daconil Ultrex. Bothproducts are labeled as fungicides andnot for moss control. They were ineff e c-tive in controlling moss under low-temperatureconditions. Some reportsindicate control at higher summer temperatures.No undesirable side effects onturf even after 15 repeat treatments.Dawn Ultra. Dawn Ultra was ineff e c-tive on moss at rates ranging from 2 to 8ounces of product/1,000 square feetwhen applied during cool, wet conditions.Dawn Ultra is marketed as a dishwashingliquid, and certified commercial pesticideapplicatorscannotlegally apply Dawn Ultra for moss control.Doing so would be the same as applyingan unregistered pesticide.Advanced screeningThe next phase involved further testingof products that showed promise formoss control and caused little or no turfi n j u r y. Products included ferrous and ferricsulfate, fatty acid soaps and copperhydroxide products. All of these havebeen tested repeatedly at several ratesand with varying numbers of repeat applications.Research results for these productsare summarized below.Iron productsNormal rates of iron for turf colorenhancement are about 0.03 poundiron/1,000 square feet. Under cool, wetconditions, rates of 0.15 to 0.20 poundiron/1,000 square feet controlled mossmarginally without injury or blackening ofProvidence creeping bentgrass turf.Ferric sulfate is more effective at killingmoss than ferrous sulfate, but bothrequire a series of five to seven treatmentsapplied at two-week intervals. Tu r fis exceptionally dark green during treatment.We achieved up to 90 percentmoss control with both ferrous and ferricsulfate, which is encouraging but not aseffective as we would like. Annual applicationsmay be necessary, and control isnot always consistent. Field test resultshave been mixed, with most tests usingferrous sulfate and reporting fair to goodGCM

RESEARCHcontrol.Copper hydroxide productsMost of our research has used Kocide2000, which is straight copper hydroxide,and Junction, which contains both copperhydroxide and mancozeb fungicide. Bothproducts show similar activity and areregistered for moss control.In western Oregon, we achieved eff e c-tive moss control with five to seven treatmentsapplied at two-week intervals atrates of 0.1 to 0.15 pound copper/1,000square feet during cool wet weatherbetween October and March. Moss injuryoccurs gradually and is progressivelygreater with each application. Am i n i m u mof five treatments is needed to prevent themoss from growing back. We normallyplan on six to seven treatments. Duringtreatment turf darkens slightly but not asdramatically as with iron products.Darkening continues into the spring evenafter treatments have been completed. Asingle treatment series of seven applicationshas provided one to two years ofacceptable moss control in our locala r e a .Potential problemsUsing copper hydroxide for mosscontrol raises several concerns. One isthe potential buildup of copper in the rootzone, which may stunt root growth. Inearly screening trials, applying the equivalentof 6 pounds of copper/1,000square feet over a one-year periodstunted root growth. Although this is fourto seven times the amount that would beapplied in a normal treatment sequence,it is still cause for concern. We nowadvise applying copper treatments nomore than two years in a row at a totalrate of 1.0 pound copper/1,000 squaref e e t / y e a r. However, surface soil levels ofcopper as high as 42 ppm have beennoted without any apparent root stuntingunder our climate conditions.Copper-induced iron chlorosis isanother concern with copper hydroxideproducts. The problem was firstobserved where copper treatments hadbeen applied on golf courses for twoconsecutive years. No problemsoccurred the first year, but severe chlorosisdeveloped the second year.Symptoms were worse on weak orshaded greens. Greens in full sun werenot affected. We concluded that thesymptoms were not phytotoxicity but ironchlorosis. Further experiments in whichwe alternated copper treatments with0.05 pound iron/1,000 square feet duringa sequence eliminated signs of chlorosis.Current recommendationsCurrent recommendations are toapply copper hydroxide products duringcool weather at 0.10-0.15 pound copper/1,000square feet at two-week intervalsfor a total of five to sevenapplications. If signs of iron chlorosisoccur during or after treatment with copperhydroxide, apply iron at 0.05 poundiron/1,000 square feet as needed toeliminate chlorosis. Iron can be tankmixedwith copper hydroxide if constantagitation is maintained in the spray solution.A minimum spray volume of 2 gallons/1,000square feet is suggested.Please note: In areas with hot, stressfulsummers where summer root loss iscommon, conduct thorough on-site testingon nursery turf to make sure coppertreatments do not cause root stuntingand thus increase the chance of turfloss during the summer.Superintendents who have usedcopper hydroxide products havereported mixed field results. In westernOregon and Washington and parts ofCalifornia, superintendents havereported excellent and fairly long-lastingcontrol without deleterious effects toturf. Other superintendents havereported short-term or partial control,and in parts of California, some havereported no control at all. Factors thatmay affect control are lack of extendedperiods of cool temperatures, lowhumidityenvironments, high soil andwater pH, and elevated salt levels in irrigationand/or spray solutions. Coppermay not be effective in these situations,but further research is clearly needed.Fatty-acid soapsSoap products have been used formany years for lawn moss control, andanecdotal reports of control with productssuch as Dawn Ultra detergent,which is not labeled as a pesticide,prompted evaluation of soap productsfor use on putting greens. We screenedseveral products based on fatty acids,all of which were effective in killingCopper-induced Iron ChlorosisRelative residual moss control in plots treated the previous winter with Junction ( Copper Hydroxide + Mancozeb),No-Mas (fatty acid soap),Daconil fungicide,and an untreated check plot.GCM 105

RESEARCHmoss. Since initial screening, we haveconcentrated on one product recentlyregistered as No-Mas, which is a 22percent active formulation of a fatty-acids a l t .Testing soap products differs fromtesting common pesticides becausethe amount of water applied as a carrierprofoundly affects the optimal rateof active ingredient. At a given rate ofactive ingredient, phytotoxicityincreases as the total volume of spraysolution decreases. After much testing,we established a rate of 0.63 gallon ofproduct/1,000 square feet applied in aminimum of 6 gallons of spray solution/1,000square feet. The same rateapplied in 12 gallons of spray solution/1,000square feet is probably optimalfor maximum moss control withoutturf injury, but it is virtually i m p o s s i b l eto achieve with most spray systems.Note: There are many soap productson the market registered for generalmoss control. They vary greatly in concentrationand recommended dilutionrates. Be sure to study specific productlabels carefully to avoid inadvertent turfinjury.Our research indicates that twoapplications applied two weeks apartgenerally achieve a high level of control.Moss kill is rapid and appears asa pronounced bleaching of mossaccompanied by a slight lightening ofturf. Turf lightening increases witheach subsequent application.Alternating soap applications with ironapplications at 0.05 pound iron/1,000square feet maintains turf color anddarkens the dead moss, improving theoverall appearance of the turf. Ironapplications can be made to soaptreatedplots the day following soapapplication. Iron will precipitate outand clog spray nozzles if it is mixedwith the soap solution.Soap treatments have been generallyeffective in western Oregon andWashington. Reports from research inCalifornia indicate poor control with winterapplications in an arid environmentwith high pH water and high pH soils. Inthe Pacific Northwest, we generallyexpect residual control during the growingseason after treatment. Long-termcontrol is not as good as for coppertreatedplots, and it appears annualtreatments will be required.Potential problemsProblems we have encounteredinclude excessive phytotoxicity whensoap applications are followed by frost.Poa annua appears to be more sensitivethan Providence creeping bentgrassunder these conditions. Occasionally turfscorching has occurred even whentreatments have been applied underoptimal conditions of mild rainy weather.Rinsing treated plots within an hour ofsoap application will generally minimizeturf scorching. Turf scorch from soapapplications is similar to a light tip burnfrom soluble fertilizer applications. Tu r frecovery is generally very rapid.Thoroughly test soap products on sitebefore using in wide-scale spray progr a m s .S u m m a r yAt some point assessing the impactof cultural practices on moss encroachmentbecomes important. The starvationtheory of putting green maintenance hasbeen followed to the point where insome cases the turf is gone and only themoss remains. Growing a dense healthystand of turf is still the best way to preventmoss from dominating turf.Superintendents should experiment withways to generate green speed otherthan starving turf to the point of thinningand mowing so low that adequate densitycannot be maintained. As long ascurrent trends in turf management continue,moss problems will persist.Once moss invades putting greens,foolproof control is impossible. T h etreatment approaches described in thispaper have provided acceptable mosscontrol in the environmental conditionsof the Pacific Northwest. According toour results, the most effective productsinclude copper hydroxide productsapplied during cool weather in sequentialapplications. Iron products appliedduring cool weather in sequential applications habeenalmoas effective, and fatty-acid soap products shogreat promise. All treatments have side effects thmust be considered. Treatments discussed in thpaper are not effective in some areas of the cout r y, and regional research is needed to fine-tutreatment programs.AcknowledgmentsPartial funding for this research has been provided by the Northwest Turfgrass Association, thOregon GCSA and Griffin LLC. Thanks to IllaheHills Country Club and superintendent BSwancutt, and Trysting Tree Golf Club and PaDoran, CGCS, for allowing us to use their facilitiefor field testing. Appreciation is also extended tnumerous undergraduate students in horticulturfor assistance in maintaining research plots.References1. Cook, T., and B. McDonald. 2002. Controllinmoss in putting greens. Turfgrass Managemenin the Pacific Northwest 5(1):4-6.2. Happ, K.E. 1998. Moss eradication in puttingreen turf. USGA Green Section Reco36(5):1-5.3. Hummel, N.W., Jr. 1988. Cultural and chemicastrategies for controlling moss (Bryum argenteum) in creeping bentgrass. A g r o n o mAbstracts 80 (Nov./Dec.):152.4. Schofield, W.B. 1992. Some common mosseof British Columbia. Royal British ColumbiMuseum, Victoria, British Columbia, Canada.Tom Cook, M.S.(cookt@mail.science.orst.edu), is an assocate professor of horticulture; BrianMcDonald is a research assistant, in thehorticulture department; and KathyMerrifield, M.S., is a senior research assistant in the department of botany and planp a t h o l o g y, all at Oregon State University,C o r v a l l i s .GCM