~ This work was partly funded by the Oregon GCSA.

Controlling mossin putting greens

RESEARCHSCIENCE FOR THE GOLF COURSE

dedicated to enriching the environment of golf

Extensive 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.

Bryum argenteum, the moss most commonly associatedwith putting greens, differs in appearancefrom common lawn mosses.

The virtual epidemic of moss on puttinggreens has prompted four years of research ona wide range of chemical control strategies.Although this research remains a work inprogress, it has revealed a great deal aboutwhat works and what doesn't and about mossgrowth in putting greens. Here we outlinecurrent control strategies and point out areasof future research.

Biology and ecologyof putting green moss

Of approximately 20 species of mossfound in association with turf in temperateclimates, Bryum argenteum, or silvery threadmoss, is the species most commonly associ-ated with putting greens. In nature, B. argen-teum is found from sea level to timberlineand from the Arctic to Antarctica. It is com-mon in cold and temperate climates but rarein tropical ones. Cosmopolitan and ubiqui-tous, it colonizes disturbed, often dry sitesand generally is considered a pioneeringspecies. It is often part of the early successionon sand dunes, bare rock and gravelly soil.Along with a small number of other mosses,it is well adapted to human-altered environ-ments, including sand-based putting greensand push-up greens that have been top-dressed regularly with sand. Unlike manymosses, it grows well in both wet, shady envi-ronments and hot, dry sites in full sun.

Like most bryophytes, B. argenteum is nota vascular plant and has no roots. It isanchored by rhiwids, which resemble rootsbut do not appear to function in uptake of

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Bryum argenteum, or silvery threadmoss, has become a common peston putting greens.

Products containing copper hydrox-ide, 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.

water or nutrients. Without xylem andphloem, it has no means to translocate foliar-absorbed nutrients. Like other mosses associ-ated with turf, B. argenteum reproduces viaspores produced in distinctive capsules and byplant fragments likely spread during mowingand other cultural practices such as coring. Todate, we have not observed spore capsules onmoss growing in putting turf

The current prevalence of moss inputting greens probably reflects recenttrends in putting green culture, includingextremely low mowing, minimal nitrogenfertilizer, increased use of sand growing

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Drought-preconditioning helps maintain a higher turf Quality under heat stress. Kentucky bluegrass at 15 days of heatstress following exposure to well-watered conditions without preconditioning (left) and two cycles of drying and re-watering (drought preconditioning) (right).

RESEARCHmediums, intense sand topdressing and lossof mercury fungicides, which were highlytoxic to moss. It occurs on both bentgrassand Poa annua greens but is by far a biggerproblem on sand-based bentgrass greens. Wehave found significant populations on first-year greens on new golf courses. It oftenshows up first in weak areas such as ridgesand mounds where grass is thin because ofscalping or drought stress. It aggressively col-onizes low, wet areas and thrives on soil-based greens with shallow layers of sandbuilt up by topdressing.

Research strategiesOur research, conducted at Oregon State

University, primarily concerns moss growingin creeping bentgrass greens, and the follow-ing results are from work done entirely onProvidence creeping bentgrass in sand-basedgrowing mediums and SR 7200 velvet bent-grass growing on soil and topdressed withsand. To date we have concentrated on large-scale broadcast treatments rather than spottreatments directed at localized infestations.Most of the chemical treatments have beenapplied during fall and winter when temper-atures range from 40 to 65 F and moisturefrom precipitation is common. Soil pH in thearea is typically 5.5 to 6.5, and salt levels arevery low.

Early screening trialsAfter unsuccessful attempts by superin-

tendents to try iron products at normal puttinggreen rates, we screened a wide range of prod-ucts by applying each at a variety of rates fromlow to very high. Products included in ourexperiments were selected because reports inthe literature indicated that they controlledmoss or that they were being applied onputting greens in an attempt to control moss.We eliminated products that caused turf dam-age and others that had no effect on the moss.The following products were tested and elim-inated from consideration.

Copper sulfate. Copper sulfate is notlabeled for moss control. In our tests, itcaused severe turf injury at rates necessary formoss kill. Caused root stunting in turf.

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 not

104 GCM I September 2002

labeled for moss control in putting greens,although some retail products are labeled formoss control in lawns. Acceptable moss con-trol but caused significant turf injury at mar-ginally high rates.

Daconil Zn and Daconil Ultrex. Bothproducts are labeled as fungicides and not formoss control. They were ineffective in con-trolling moss under low-temperature condi-tions. Some reports indicate control at highersummer temperatures. No undesirable sideeffects on turf even after 15 repeat treatments.

Dawn Ultra. Dawn Ultra was ineffectiveon moss at rates ranging from 2 to 8 ouncesof product/1,000 square feet when appliedduring cool, wet conditions. Dawn Ultra ismarketed as a dishwashing liquid, and certi-fied commercial pesticide applicators cannotlegally apply Dawn Ultra for moss control.Doing so would be the same as applying anunregistered pesticide.

Advanced screeningThe next phase involved further testing of

products that showed promise for moss con-trol and caused little or no turf injury.Products included ferrous and ferric sulfate,fatty acid soaps and copper hydroxide prod-ucts. All of these have been tested repeatedlyat several rates and with varying numbers ofrepeat applications. Research results for theseproducts are summarized below.

Iron prOductsNormal rates of iron for turf color

enhancement are about 0.03 poundiron/1,000 square feet. Under cool, wet con-ditions, rates of 0.15 to 0.20 poundiron/1,000 square feet controlled moss mar-ginally without injury or blackening ofProvidence creeping bentgrass turf. Ferricsulfate is more effective at killing moss thanferrous sulfate, but both require a series offive to seven treatments applied at two-weekintervals. Turf is exceptionally dark greenduring treatment. We achieved up to 90 per-cent moss control with both ferrous and fer-ric sulfate, which is encouraging but not aseffective as we would like. Annual applica-tions may be necessary, and control is notalways consistent. Field test results have beenmixed, with most tests using ferrous sulfateand reporting fair to good control.

Copper hydroxide productsMost of our research has used Kocide

2000, which is straight copper hydroxide,and Junction, which contains both copperhydroxide and mancozeb fungicide. Bothproducts show similar activity and are regis-tered for moss control.

In western Oregon, we achieved effectivemoss control with five to seven treatmentsapplied at two-week intervals at rates of 0.1 to

0.15 pound copper/1,000 square feet during

Copper-induced iron chlorosis on putting green turf can be prevented by tank-mixing copper with iron or following cop-per treatments with iron applications.

cool wet weather between October andMarch. Moss injury occurs gradually and isprogressively greater with each application. Aminimum of five treatments is needed to pre-vent the moss from growing back. We nor-mally plan on six to seven treatments. Duringtreatment turf darkens slightly but not as dra-matically as with iron products. Darkeningcontinues into the spring even after treatmentshave been completed. A single treatment seriesof seven applications has provided one to twoyears of acceptable moss control in our localarea.

Potential problemsUsing copper hydroxide for moss control

raises several concerns. One is the potentialbuildup of copper in the root zone, whichmay stunt root growth. In early screeningtrials, applying the equivalent of 6 pounds ofcopper/l,OOO square feet over a one-yearperiod stunted root growth. Although this isfour to seven times the amount that wouldbe applied in a normal treatment sequence,it is still cause for concern. We now adviseapplying copper treatments no more thantwo years in a row at a total rate of 1.0pound copper/l ,000 square feet/year.However, surface soil levels of copper as highas 42 ppm have been noted without anyapparent root stunting under our climateconditions.

Copper-induced iron chlorosis is anotherconcern with copper hydroxide products.The problem was first observed where cop-per treatments had been applied on golfcourses for two consecutive years. No prob-lems occurred the first year, but severechlorosis developed the second year.Symptoms were worse on weak or shadedgreens. Greens in full sun were not affected.We concluded that the symptoms were notphytotoxicity but iron chlorosis. Furtherexperiments in which we alternated coppertreatments with 0.05 pound iron/l,OOOsquare feet during a sequence eliminatedsigns of chlorosis.

Current recommendationsCurrent recommendations are to apply

copper hydroxide products during coolweather at 0.10-0.15 pound copper/l,OOOsquare feet at two-week intervals for a totalof five to seven applications. If signs of ironchlorosis occur during or after treatment

with copper hydroxide, apply iron at 0.05pound iron/l,OOO square feet as needed to

eliminate chlorosis. Iron can be tank-mixedwith copper hydroxide if constant agitationis maintained in the spray solution. A min-imum spray volume of 2 gallons/l,OOOsquare feet is suggested.

Please note: In areas with hot, stressfUlsummers where summer root loss is common,conduct thorough on-site testing on nurseryturf to make sure copper treatments do notcause root stunting and thus increase thechance of turf loss during the summer.

Superintendents who have used copperhydroxide products have reported mixedfield results. In western Oregon andWashington and parts of California, super-intendents have reported excellent andfairly long-lasting control without deleteri-ous effects to turf. Other superintendentshave reported short-term or partial control,and in parts of California, some havereported no control at all. Factors that mayaffect control are lack of extended periods ofcool temperatures, low-humidity environ-ments, high soil and water pH, and elevatedsalt levels in irrigation and/or spray solu-tions. Copper may not be effective in thesesituations, but further research is clearlyneeded.

RESEARCHFatty-acid soaps

Soap products have been used for manyyears for lawn moss control, and anecdotalreports of control with products such asDawn Ultra detergent, which is not labeledas a pesticide, prompted evaluation of soapproducts for use on purring greens. Wescreened several products based on fattyacids, all of which were effective in killingmoss. Since initial screening, we have con-centrated on one product recently regis-tered as No-Mas, which is a 22 percentactive formulation of a fatty-acid salt.

Testing soap products differs from test-ing common pesticides because theamount of water applied as a carrier pro-foundly affects the optimal rate of activeingredient. At a given rate of active ingre-dient, phytotoxicity increases as the totalvolume of spray solution decreases. Aftermuch testing, we established a rate of 0.63gallon of product/l,OOO square feetapplied in a minimum of 6 gallons ofspray solution/l,OOO square feet. Thesame rate applied in 12 gallons of spraysolution/l,OOO square feet is probablyoptimal for maximum moss control with-out turf injury, but it is virtually impossi-ble to achieve with most spray systems.

Note: There are many soapproducts on themarket registered for general moss control.

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Fallow-up applications of iron can mask the lightening effect of soaps on turf.

RESEARCHThey vary greatly in concentration and rec-ommended dilution rates.Be sure to study spe-cific product labels carefully to avoidinadvertent turf injury.

Our research indicates that two appli-cations applied two weeks apart generallyachieve a high level of control. Moss killis rapid and appears as a pronouncedbleaching of moss accompanied by aslight lightening of turf. Turf lighteningincreases with each subsequent applica-tion. Alternating soap applications withiron applications at 0.05 poundiron/l,OOO square feet maintains turfcolor and darkens the dead moss, improv-ing the overall appearance of the turf.Iron applications can be made to soap-treated plots the day following soapapplication. Iron will precipitate out andclog spray nozzles if it is mixed with thesoap solution.

Soap treatments have been generallyeffective in western Oregon andWashington. Reports from research inCalifornia indicate poor control with win-ter applications in an arid environmentwith high pH water and high pH soils. Inthe PacificNorthwest, we generally expectresidual control during the growing seasonafter treatment. Long-term control is not asgood as for copper-treated plots, and itappears annual treatments will be required.

Potential problemsProblems we have encountered include

excessivephytotoxicity when soap applica-tions are followed by frost. Poa annuaappears to be more sensitive thanProvidence creeping bentgrass under theseconditions. Occasionally turf scorching hasoccurred even when treatments have beenapplied under optimal conditions of mildrainy weather. Rinsing treated plots withinan hour of soap application will generallyminimize turf scorching. Turf scorch fromsoap applications is similar to a light tipburn from soluble fertilizer applications.Turf recovery is generally very rapid.Thoroughly test soap products on sitebefore using in wide-scale spray programs.

SummaryAt some point assessing the impact of

106 GeM I September 2002

cultural practices on moss encroachmentbecomes important. The starvation theoryof purring green maintenance has been fol-lowed to the point where in some cases therurf is gone and only the moss remains.Growing a dense healthy stand of turf is stillthe best way to prevent moss from domi-nating turf Superintendents should exper-iment with ways to generate green speedother than starving turf to the point of thin-ning and mowing so low that adequate den-sity cannot be maintained. As long ascurrent trends in turf management con-tinue, moss problems will persist.

Once moss invades putting greens,foolproof control is impossible. Thetreatment approaches described in thispaper have provided acceptable moss con-trol in the environmental conditions of thePacificNorthwest. According to our results,the most effective products include copperhydroxide products applied during coolweather in sequential applications. Ironproducts applied during cool weather insequential applications have been almostas effective, and fatty-acid soap productsshow great promise. All treatments haveside effects that must be considered.Treatments discussed in this paper are noteffective in some areas of the country, andregional research is needed to fine-tunetreatment programs.

AcknowledgmentsPartial funding for this research has been provided

by the Northwest Turfgrass Association, the OregonGCSA and Griffin LLC. Thanks to IIlahee Hills CountryClub and superintendent Bill Swancutt, and Trysting TreeGolf Club and Pat Doran, CGCS, for allowing us to usetheir facilities for field testing. Appreciation is alsoextended to numerous undergraduate students in horti-culture for assistance in maintaining research plots.

References1. Cook, 1, and B. McDonald. 2002. Controlling moss

in putting greens. Turfgrass Management in thePacific Northwest 5(1 ):4-6.

2. Happ, K.E. 1998. Moss eradication in putting greenturf. USGAGreen Section Record 36(5):1-5.

3. Hummel, NW., Jr. 1988. Cultural and chemicalstrategies for controlling moss (Bryum argenteum)in creeping bentgrass. Agronomy Abstracts 80(Nov./Dec.): 152.

4. Schofield, WB. 1992. Some common mosses ofBritish Columbia. Royal British Columbia Museum,Victoria, British Columbia, Canada.

Tom Cook, M.S. (cookt@mail.science.orst.edu), isan associate professor of horticulture; Brian

McDonald is a research assistant, in the horticul-ture department; and Kathy Merrifield, M.S., is a

senior research assistant in the department ofbotany and plant pathology, all at Oregon State

University, Corvallis.