Moss Infestations in Putting GreensEradication by electromotive destruction of cWorophyll.

BY ARTHUR P. WEBER AND THOMAS O. McAVOY

Figure I.When moss is viewed in cross-section. it has a sponge-like appearance and is densely packedwith very small voids.

The proliferation of moss infesta-tions in putting greens can becorrelated to the asymptotic

lowering of mower heights in the pur-suit of "fast green speeds."The side effect,stressing and thinning the turf cover,promotes the invasion of undesirablespecies, e.g., moss, to impair the con-sistency of the green surface as aputting medium (1).

Of the about 9,500 purported mossvariations, Bryum argentium, commonlyknown as silvery thread moss, has beenidentified as the dominant invasivespecies. The botanical phylum Briophataincludes mosses and liverworts, thesimplest ofland-dwelling plants which,from fossil records dating back some400 million years, prevail as enduring

primitive species whose morphology,growth, and survival characteristics differradically from higher plants, e.g., theputting green turf grasses within whichthey coexist.

BIOLOGYMosses do not have roots and, in theirabsence, the plants anchor to a surfacewith rhyzoids attached to a substrate.Consequently, mosses can thrive onsurfaces as dissimilar as rocks, concretewalks, and masonry walls. Neither domosses have a defined vascular systemfor water and nutrient delivery or, con-versely, as a pathway to facilitate controlor eradication.

Mosses survive long periods ofdrought, dehydrate, and sustain pro-

longed dormancy, to then resumephotosynthesis upon rehydration.~ceptors ~nd patterns of water uptakehave been advariced, the modus operandiof which remain obscure. Uniquely,water uptake by Bryum argentium iscomparatively rapid, categorizing theplant as being ectohydric (2,3,4,5).

MORPHOLOGYBryum argentium moss infestationsprevail as sponge-like biomasses which,when microscopically viewed in cross-section, provide a densely packedlabyrinth of minuscule voids and inter-stices. Photomicrographs, depicted inFigure 1, were taken at lOx, 30x, and63x magnification to correspondinglydecreasing 22mm, 13mm, and 3.5mmfields of view, using a Nikon SMZZoom Stereo Microscope with a lxobjective lens and Nikon Coolpix 45004 megapixel digital camera.

Given that the surface-to-volumeratios of voids vary inversely with sizeand shape, Bryum argentium infestationscomparatively interface to their ambientenvironment with an extraordinarilyhigh biomass surface relative to volume.This key attribute, in the absence ofroot hairs to absorb water and leafstomata to respire carbon dioxide andoxygen, ~erves to sustain photosynthesisby extended surface adsorption andabsorption.

ECOLOGYAlthough Bryum argentium persistswithin a broad divergence of ambientparameters, remarkable exceptions havebeen metal-contaminated soils. Thetoxicity sequence has been found to beHg > Cu > Pb > Ni > Cd > Zn >

32 GREEN SECTION RECORD

Mg, the heavy metals being the mosttoxic. Mercury (Hg) based managementcontrols, particularly, had been found tobe highly effective but were discardedfor not being environmentally viable.Recently, application programs usingcopper hydroxide-based fungicides havebeen advanced for post-emergence mosscontrol (6,7,8,9,10,11,12,13,14,15,16).

ELECTROCHEMISTRYThe toxicity response to metals byBryum argentium parallels the ActivitySeries, i.e., an arrangement of metals inthe order of their tendency to reactwith water and acids so that each metalin the series displaces from solutionthose below it and is displaced by thoseabove it. Because the displacementsinvolve the transfer of electrons fromthe reducing agent to the oxidizingagent and may be used as a source ofelectric current, the Activity Series isalso known as the Electromotive Series.

To obtain this result, the oxidation/reduction reaction must take place inan appropriate apparatus, e.g., a batterycell, so constructed that the transfer ofelectrons from one atom to the other, asa current between electrodes, takesplace along an intervening conductor.However, sufficient energy, in the formof a relative potential difference betweenthe electrodes, must be made availableas an electromotive force to overcomeany interposed resistance to the electroncurrent flow from the reducing agentto the oxidizing agent.

METAL ELECTRODEPOTENTIALSIn order to compare the electrodepotentials between metals and theirsolutions, it is customary to use solu-tions in which the concentration of themetal ions is "Normal," i.e., molar. Asa basis for comparison, inasmuch asabsolute electrode potentials cannot bedetermined with reasonable accuracy,the potential of a platinum electrodesaturated with hydrogen gas under oneatmosphere pressure against a solutionthat is "Normal" with respect to the

Shade and contours on this green contribute to a poor growing environment. As the area is scalped,moss becomes more competitive, dominating the area.

JULY-AUGUST 2003 33

Figure 2Activity Series alkJa Electromotive Series

Potentials of elements in contact with normal concentration of the ion at 25°C

VERIFICATIONIn support of the hypothesis, mossinfestations at the Old Westbury Golfand Country Club, OldWestbury, NewYork, were totally and permanentlyeradicated by spot drenching with lowapplication rates of highly dilutedaqueous solutions of silver nitrate. Sur-rounding grass plants remained vigorousinasmuch as the topical application andpenetration of the required silverdosage attenuated short of the grassplant rootzones. By-product nitrate insolution remained as a turf repairnutrient.

To experimentally verify that thechlorophyll had been electromotivallydestroyed, a battery cell was assembled.Harvested Bryum argentium moss out-croppings (the cathode) were steepedin water containing a trace of salinityas a conductive electrolyte and wereseparated by a diaphragm from aqueous

between the ions is large enough topermit the Mg- ion to be oxidized bylosing and transporting its electron toreduce the Hg+ ion to metallicmercury.

The decreasing relative electrodepotential difference between the metalsof higher ranking than mercury in theActivity Series is apparently insufficientas a driving force to overcome themolecular binding energy of the Mg-electron in chlorophyll and resistanceto the conduction of the electron inBryum argentium, wherein chlorophyllfunctions as the negative electrode of agalvanic cell. Significantly, copper wasempirically found to be the nearesttoxicity competitor to mercury and, asit turns out, ranks just above mercury inthe Activity Series, with a relative CuH

cupric ion electrode potential of +0.34volt, or relatively 0.79 - 0.34 = 0.45volt less than a mercuric ion.

Theoretically, the Activity Seriesforecasts that silver, developing at leastthe same relative electrode potential asmercury, would galvanically destroy thechlorophyll in Bryum argentium aseffectively as mercury.

Figure 3Chlorophyll

CH--C---C-CH-CH'I I 1

CH,CH--C, /,C-CH CH,I I N I I

HC-C + I + __ C-CI N-=Mg~N I

HC-C~ I ..........C-CI I /N, I ICH,C-C C-CH C,H.

, I I I ICH,CH P---C-CH,

~~"at-ar-'b .' 'COaCH,

HYPOTHESISHeavy metals elicit a toxic responsefrom Bryum argentium because of theelectromotive destruction of thechlorophyll. The electrical resistancebetween the negatively charged mag-nesium ion at the core of a chlorophyllmolecule and, say,a surface interfacedpositively charged mercury ion is suchthat the relative potential difference

Figure 3). It is a photoreceptor up to700mm and transfers such radiantenergy to its chemical environment,thus acting as a transducer in photo-synthesis (17).

Potential PotentialElement JQn inVolts Element Ion inVolts

I{ K+ -2.92 H2 H+ 0.00Na Na+ ~2.71 Sb SB+H +0.10Ca CaH -2.5(?) As As+++ +0.3(?)Mg MgH -1.55 Cu CuH +0.34AI AI+H -1.34 Cu Cu+ +0.47Zn

ll~

ZnH -0.75 Hg Ht +0.79I'

Fe FeH -0.44 Ag Ag+ +0.80Cd CdH -0.40 Hg HgH +0.86Co COH -0.24 Au Au+ + 1.5(?)Ni NiH -0.22 O2 OH- +0.11Sn SnH -0.14 12 1- +0.62Pb PbH -0.12 Br2 Br- +1.08Fe Fe+++ -0.04 CI2 CI- +1.35

F2 F- + 1.9(?)

CHLOROPHYLLThe green pigment essential to photo-synthesis, chlorophyll, is a porphorinstructured molecule containing ahydrophilic carbocyclic ring with alipophilic phytyl tail, nitrogen bridgedfrom a negatively charged magnesiumion at the core of the molecule (see

hydrogen ions is called zero. Figure 2comparatively tabulates the relativeelectrode potenti.als, expressed in volts,.of various elements at 25°C in contactwith solutions that are "Normal" with.respect to their ions, thereby electro-motivally quantifying the ActivitySeries.

From Figure 2, the limiting potentialdifference across a battery cell, measuredin volts, can be calculated. For example,metallic magnesium, in contact with a"Normal" MgH ion solution, acquires anegative potential of -1.55 volts, whilemercury in contact with a "Normal"Hg+ ion solution acquires a positivepotential of +0.79 volts. The limitingvoltage, therefore, across the electrodesof such a magnesium/mercury batterycell would be the algebraic differencebetween the relative electrode potentials:+0.79 - (-1.55) = 2.34 volts.

34 G R E ENS E C T ION R E COR 0

A battery cell was constructed to verify that the chlorophyll had been electromotively destroyed.

silver nitrate solution (the anode). Theinduced electron current flow wasindicated by a voltage difference acrossthe immersed cathode and anodeterminals of a calibrated multi-meter.Chlorophyll destruction caused themoss to blacken around the cathodeterminal and metallic silver to depositon the anode terminal.

The battery was assembled within a6 fl. oz. transparent glass screw-top jar,2% in. diameter by 2% in. high. Thediaphragm, a hollow cardboard cylinder,centrally positioned and epoxy affixedwithin the jar, was % in. outside diameterby .Yt6 in. thick, and stood 2% in. high. Todisplace excess volume, the annulus

around the cylindrical diaphragm washalf-filled with glass beads, on top ofwhich 10 grams of harvested Bryumargentium was steeped in 100 ml of a0.01 % saline aqueous solution. The coreof the cylindrical diaphragm was filledwith 23 ml of 0.22% silver nitrate solu-tion (0.14% silver).The multi-meterindicated a direct current voltage thatpeaked and dwelled at 0.6 volt for some90 minutes before gradually diminish-ing as the chlorophyll was destroyedand the battery cell exhausted.

FIELD TRIALSThe putting greens in the study, con-structed in 1962, were the "push-up"

type, sand amended, approximately 70%creeping bentgrass (Pencross) and 30%annual bluegrass (Paa annua), double cutdaily at VB in. mower bedknife height tonot less than 9Yzft. Stimpmeter speed,fed lYzlbs. of nitrogen per 1,000 sq. ft.per year, preventively fungicide treated,verticut, and topdressed bimonthly inseason. The trials remained ongoingthroughout the 2002 calendar year.

Only one application, with a mini-mum aqueous solution concentrationof 0.22 weight percent silver nitrate(0.14 weight percent silver), prepared bydissolving 1 gram of silver nitrate in16 fl. oz. of water, and spot treated bydrenching at the rate of 1 fl. oz. per

6 sq. in. of moss outcroppings, in everyinstance and under all environmentaland ecological conditions successfullyeradicated moss infestations, withoutsemblance of reemergence. Treated anderadicated moss outcroppings appear asdarkened areas.

SUMMARYEstablishment of silvery thread moss(Bryum argentium) populations in puttinggreens has been exacerbated by thelowering of mower bedknife heights tocomply with golfers' preference for fastgreens.

In the absence of roots or a definedvascular system, but configured with an

uncommonly high biomass surface-to-volume interface, moss populationssustain photosynthesis by ectohydrichydration and respiration within broadenvironmental conditions. Remarkableexceptions have been metal-contami-nated soils.

The toxicity response of Bryumargentium to metals correlates to therelative electrode potentials of metalsand their solutions in the ActivitySeries, a/k/ a the Electromotive Series.The heavier the metal, the greater, too,is the relative potential difference withthe porphorin structured magnesiumcore of chlorophyll molecules essentialto photosynthesis. Consistent with thetoxicity correlation of the ActivitySeries, mercury-based controls havebeen effective, but not being environ-mentally acceptable, they have beendiscarded. Copper, the metal rankedimmediately above mercury in theActivity Series, falls short of the mark.

We hypothesize that the toxicresponse to heavy metals results fromthe electromotive destruction of thechlorophyll. The Activity Series fore-casts that silver would as effectivelydestroy the chlorophyll in Bryumargentium as does mercury, the relativepotential difference being sufficient toelectromotively cause the negativelycharged magnesium ion core of chloro-phyll to oxidize and release its electronto reduce a positively charged silver ionto metallic silver. The assembly of aworking Bryum argentium/ silver nitratebattery cell experimentally confirmedboth the hypothesis and the forecast.

Silvery thread moss in 70% bentgrass/30% annual bluegrass putting greenswas successfully eradicated duringongoing year-round field trials, at lowapplication rates of highly diluted silvernitrate solutions, without adverselyaffecting the vigor of surrounding grassplants (patent pending).

BIBLIOGRAPHY1. Happ, Keith A. 1998."Moss Eradication in

Putting Green Turf," USGA Green SectionRecord, Sept./Oct. 1998.

JULY-AUGUST 2003 35

Top: Over the years, golf course superintendents have tried iron sulfate as a control formoss encroachment, but oftentimes the result was incomplete control of the problem.Above: Silver nitrate was used to spot-treat moss in the research plots. Treated anderadicated moss outcroppings appeared as darkened areas.

2. Moore, C. S., and G.A.M. Scott. 1979.] Bryol., 10:291-311.

3. Bunch, H. 1945."Uber die Wasser-undMineralstoff-versongung der moose,"Commentat, BioI. Sd., Fenn 9(16), 1-44.

4. Chopra, R. N., and P. K. Kumra. 1988."Alternative Pathways in Life Cycle;' Biologyof Bryophysics, 5:107-127.

5. Chopra, R. N., and P. K. Kumra. 1988."Alternative Pathways in Life Cycle," Biologyof Bryophysics, 12:308-311.

6. Richardson, D.H.S. 1981."Structure andClassification;' Biology of Mosses, Halsted PressU.S.A., 1:1-5; 10:155-161.

7. Neibocor, E., and D.H.S. Richardson. 1980."The Replacement of the NondescriptTerm Heavy Metals by a Biologically andChemically Significant Classification ofMetal Ions," Environmental Pollution (ser.B),1:3-26.

8. Coombes,A.]., and N.W Lepp. 1974."TheEffect of Cu and Zn on the Growth ofMarchantia polymorpha and Funariahygrometrica;' Bryologist, 77:447-452.

9. Hummel, Norman W 1988. "An IntegratedApproach to Moss Control in Golf CourseGreens;' Research Experiment, CornellUniversity.

10. Simola, 1. K. 1977."Growth and Ultrastruc-ture of Sphagnum fimbriatum Cultured withArsenate, Fluoride, Mercury, and CopperIons,"] Hattori Bot. LAb., 79:147-155.

36 GREEN SECTION RECORD

11. Shaw,]. A. 1991."Ecological Genetics, Evolu-tionary Constraints, and the Systerpatics ofBryophytes;' Advances in Bryology, 4:29-74.

12.Taylor,]., and K. Danneberger. 1996."Mosson Greens When the Rolling Stone Stops;'Golf Course Management, 64(9):53-56.

13. Golf Course Superintendents. 1997."MossControl Survey," Northern Ohio TuifgrassNewsletter.

14. Hummel, Norman W 1994."Methods forMoss Control," Golf Course ManagementResearch Report, 65(3):106-110.

15. Rossi, F. S. 2002. "Moss Control Research atCornell University;' Summary of 2002Research.

16. Dudones, D.W 2002. "Silvery Thread Moss(Bryum argentium) Population ReductionStrategies for Golf Course Putting Greens,"M.S. Thesis, Cornell University.

17. Condensed Chemical Dictionary, 12th Ed"Richard]. Lewis, Sr.,Van Nostrand Reinhold,NY

DR. ARTHUR P WEBER, a chemicalengineer, has been a member of the USGAGreen Section Committee since 1984.THOMAS O. McAvoy, CGCS, is super-intendent at Old VJ.-rstburyGolf Club(New York).