Managing silvery thread moss in creeping bentgrass greens · Managing silvery thread moss in creeping bentgrass greens Some products provide control of an increasingly common plant

RESEARCH

Managing silvery thread mossin creeping bentgrass greensSome products provide control of an increasingly common plant pest in creeping bentgrass greens.

Fred H. Yelverton, Ph.D.

Figure 1. Moss on creeping bentgrass greens [s now a problem throughout the world, including Japan.

Twenty years ago, moss was a minor prob-lem on golf courses and was usually restrictedto mild, moist climates (1). Moss is now amajor weed on many creeping bentgrass(Agrostispalustris) putting greens and can befound in most areas of the world where creep-ing bentgrass greens exist, including Australia,Mexico and the Middle East (Figure 1). In thepast, moss problems on greens in the UnitedStates were confined to areas such as thePacific Northwest, New England and highelevations of the Rocky Mountains in theWest and the Blue Ridge and Great SmokyMountains in the East (10). In NorthCarolina, the most severe problems have his-torically occurred on golf courses with sand-based putting greens at elevations above 2,000feet. In recent years, moss problems havespread to the coastal areas of North Carolina,which can be considered the edge of thesouthern range of creeping bentgrass greens.

Although it is unclear why moss has beensteadily increasing in severity and distribution,increasing infestations are likely due to a com-bination of lower mowing heights, reducedfertility and discontinued use of mercury-based fungicides (4,6). In other words, turf-grass vigor has been reduced to the point thatgreens are more prone to weed encroachment,including moss invasion (1,3,8).

In research conducted at North CarolinaState University, mercury-based fungicidessuch as PMAS, mercury chloride andcalochlor have successfully controlled moss(11). Furthermore, superintendents who havedealt with moss for years frequently remarkthat one of the best management practices forreducing moss infestations is to' raise themowing height. Additional evidence thatreduced mowing heights are contributing tothe problem is that initial moss infestations

are often found on more easily scalped areassuch as mounds or ridges on putting greens.

Biology of mossLimited knowledge of both the biology

and management of moss has increasedmany superintendents' concerns about man-aging this pest on putting greens. The fossilrecord shows that mosses are primitive plantsthat have changed little over the past 350 mil-lion years (5). True mosses differ from higherplants, including turf grasses, because they arenonvascular (lack a phloem and xylem) andhave no true roots (1). Control strategies atedictated by the plant's biology. Becausemosses lack a vascular system, systemic herbi-cides cannot be translocated within the plant

and are therefore useless.Mosses absorb water and nutrients

through structures called rhizoids (5).Mosses are adapted to a wide range of envi-ronments, from sidewalks and patios towooded areas (3), and they typically becomeestablished on rocks, tree trunks and otherinhospitable locations during cool, dampperiods. They survive hot, dry spells bybecoming semidormant and resume growthwhen weather conditions are favorable (7). Asan example of their adaptability, silverythread moss (Bryum argentum) may remainviable after two years of desiccation. (7).

ReproductionMosses are perennial plants that reproduce

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Figure 2. Silvery thread moss (Bryum argentum) has a distinctive silver sheen that can be easily seen on a creepingbentgrass putting green.

RESEARCHby spores (sexual reproduction) or vegetatively(asexual reproduction). Mosses are probablyintroduced onto greens by spores. Mossplants release spores, which are carried greatdistances by wind. The spores land on a moistor damp host and develop into new plants,especially where there is little or no competi-tion for space or resources from other plants(7). Asexual or vegetative reproduction, how-ever, can be facilitated by water, wind, foottraffic and maintenance equipment. Forexample, a moss plant cut by a golfer's shoecan be then transported to another area of thecourse. Moss can grow from small pieces of ashoot or even leaves. Ease of disseminationand variety of reproductive life cycles makemoss a challenging pest on putting greens.

SpeciesThere are approximately 9,500 species of

moss, but only four have been identified onputting greens. By far the most common mosson creeping bentgrass putting greens is silverythread moss (Bryum argentum), which is, todate, the only moss species found on puttinggreens in North Carolina. This species of mossgets its name from its silvery appearance,which is easily visible on a creeping bentgrassputting green (Figure 2).

Controlling silvery thread mossTo combat the ever-increasing invasion of

silvery thread moss on creeping bentgrassgreens, researchers across the United Statesand several countries have tested variousapproaches that include herbicides, fungi-cides, fertilizers, cultural practices and homeremedies. Over the past several years, we haveinvestigated various strategies for the controlof silvery thread moss. The following is a dis-cussion of various approaches that haveshown promise from a research perspective. Itis important to point out that the followingdiscussion is a summary of research resultsand not control recommendations.

For the following discussion, field experi-ments were conducted at two golf courses, ElkRiver Country Club, Banner Elk, N.C., andJefferson Landing Golf Club, West Jefferson,N.C. Putting greens at both locations werebuilt to USGA recommendations: 85%-90%sand, 10%-15% peat, less than 1% silt and apH of 6.2. The mowing height was 0.125 inch(3.2 millimeters) at both locations. Puttinggreens received a total of2.72 pounds of nitro-gen/l ,000 square feet (293 kilograms/hectare)from March to September at Elk River;Jefferson Landing was fertilized year-roundwith a total of2.68 pounds of nitrogen/l,OOOsquare feet (288 kilograms/hectare).

Percent moss reduction was determinedby the change in initial moss population fromthe application time to a certain time aftertreatment. The following formula was used:

[(mosso - moss.) ]---- x 100,

mosso

where mosso is the percentage of silvery threadmoss cover at time of application and moss.is the percentage of moss cover at x weeksafter treatments were applied.

Treatment comparisons

Fertilizers with iron and RonstarTreatments included Ironizer, a 4-0-0-

18% iron fertilizer derived from ferrous sul-fate, ferrous oxide and iron humate; Ironite,a 1-0-0-12% iron fertilizer derived from irondisulfide and iron sulfate; and ferrous sulfateplus ammonium sulfate. The 2% granularformulation of Ronstar (oxadiazon) was alsoused in these experiments.

Initial applications were made Aug. 16,1999, and Sept. 13, 2000, at JeffersonLanding and July 3, 1999, and Aug. 3, 2000,at Elk River. All treatments except Ronstarwere applied twice at week zero, the first weekin which treatments were applied, and twiceat four weeks after initial application. Ronstarwas applied only once, at week zero.

Before application, the Ironizer andIronite were ground to reduce particle size.Approximately 15 minutes after granularapplication, both sites were irrigated with 0.2inch (0.5 centimeter) of water. The ferroussulfate plus ammonium sulfate treatmentswere applied with 8,003 extended-rangeflat-fan nozzles at a spray volume of 80 gallonsper acre (748.3 liters/hectare).

Treatments containing iron were moreeffective than treatments that did not containiron in reducing silvery thread moss popula-tions (Table 1). In addition, treatments thatcontained iron enhanced creeping bentgrassquality (data not shown). Iron applicationshave a desiccating effect on moss, and it hasbeen previously reported that iron applica-tions increase vegetative growth of creepingbentgrass, thereby increasing its ability tocompete with unwanted species (9). At 10weeks after the initial application, bothlronizer and ferrous sulfate plus ammoniumsulfate appeared to be more effective thanIronite in reducing silvery thread moss. (At sixweeks after the initial application, there wasno significant difference among the threetreatments.) This is most likely because of thegreater amounts of iron and nitrogen appliedwith these treatments. In addition, ferrous

104 GCMMarch 2005

IRON VS. MOSS

Population reduction (%)*

Weeks after initial treatmentTreatmentt Rate 6 10

lronizer 2.6 pounds iron/1,000 ft2 81 68126.9 kilograms/hectare

lronizer + Ronstar 2.6 pounds iron/1,000 ft2 83 58+ 1.5 pounds active ingredienVacre126.9 kilograms/hectare+ 1.7 kilograms/hectare

lronite 0.7 pound iron /1,000 sq. ft. 69 734.2 kilograms/hectare

lronite + Ronstar 0.7 pound iron /1,000 sq. ft 73 34+ 1.7 pounds active ingredienVacre34.2 kilograms/hectare+ 1.9 kilograms/hectare

Ferrous sulfate + 0.8 pound iron /1,000 sq. ft. 87 67ammonium sulfate' + 0.6 pound nitrogen/1,000 sq. ft.

39.1 kilograms/hectare+29.3 kilograms/hectare

Ronstar 1.5 pounds active ingredienVacre 38 261.7 kilograms/hectare

Not treated 22 -9

LSD 38 49

- -- - -- - contrasts*- - - - - - -

Iron vs. no Iron S S

lronizar vs. lronite NS S

Ronstar VS. no Ronstar NS NS

Note. Data are averaged over years (1999 and 2000) and locations.*Percent reduction in moss population at six and 10 weeks was calculated by comparing moss population perplot with initial moss population. A positive number denotes a decrease in moss population; a negative num-ber denotes an increase in moss population.tAli treatments were applied twice at week zero and at four weeks after initial treatment except Ronstar,whichwas applied only once at week zero.IS, significant differences between the two treatments; NS, differences between the two treatments are notsignificant.

Table 1. Effect of fertilizer and Ronstar treatments on percent reduction in silvery thread moss populations.

RESEARCHsulfate and the iron fertilizers in Ironizer pro-vide an immediate release of iron, whereasIronite releases iron more slowly.

The addition of Ronstar to the fertilizertreatments did not improve control of silverythread moss over treatments that did not con-tain Ronstar (Table 1). Ronstar has been pre-viously reported to reduce silvery thread mosspopulations (2). This was not observed inthese trials. However, a difference in applica-tion timing may account for the differentresults. In earlier research (2), Ronstar wasapplied in March; in these trials, Ronstar wasapplied later in the year.

Daconil Weather Stik and Daconil ZnDaconil (chlorothalonil) with and without

zinc at two different rates was applied at either5 or 10 gallons of water per 1,000 square feet(2,037.3 or 4,074 liters/hectare). Treatmentswere applied with 8,008 extended-range flat-fan nozzles. Treatments were repeated twoweeks after the initial application. The highvolumes of water were achieved by calibratingto 2.5 gallons/1,000 square feet (1,018.6liters/hectare) and spraying the plots eithertwo or four times, depending on the desiredvolumes. Initial applications at Elk River in1999 and 2000 took place on June 15 andJuly 3, respectively. The initial application atJefferson Landing in 1999 was on Aug. 16.

Daconil, particularly at the JeffersonLanding location, was effective in reducing sil-very thread moss populations (Tables .2, 3;Figure 3). According to contrasts (data notshown), no difference in control of silverythread moss was observed among Daconil for-mulations, Daconil rates or spray volumes.

The moss at Elk River showed reducedphytotoxicity because rainfall occurred withinone hour after application in 1999 and within24 hours after the repeat application in 2000;the rainfall limited the drying of Daconil andtherefore reduced efficacy. Daconil treatmentsdid not reduce creeping bentgrass quality atany location or rating date. It should also benoted that in other research (data not shown),Daconil Weather Stik performed better on sil-very thread moss when temperatures wereabout 80 F (26.6 C). Applications in coolweather have been shown to have limitedeffectiveness.

SummarySilvery thread moss is becoming an

increasing problem on golf course putting

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DACONIL VS. MOSS, ELK RIVER

RESEARCHgreens throughout the world. Even thoughmosses have been around for millions of years,only recently has this plant become a problemon golf courses. Although it is debatable whymoss has recently become a problem, themost likely explanations involve a change incultural and pest management practices onbentgrass greens. Specifically, lower mowingheights and an elimination of mercury-basedfungicides appear to be the most commonlyaccepted reasons.

AcknowledgmentsThe North Carolina Turfgrass Foundation sponsored

this research. Figure 3. Multiple applications of Daconil (chlorothalonil) provide control of silvery thread moss.

Daconiltreatmentt Rate Volume

Without zinc 8.1 pounds/acre 5 gallons/1 ,000 sq. ft.9.1 kilograms/hectare 2,037.3 liters/hectare

Without zinc 16.2 pounds/acre 5 gallons/1,000 sq. ft18.2 kilograms/hectare 2,037.3 liters/hectare

Without zinc 8.1 pounds/acre 10 gallons/1 ,000 sq. ft9.1 kilograms/hectare 4,074 liters/hectare

Without zinc 16.2 pounds/acre 10 gallons/1 ,000 sq. ft18.2 kilograms/hectare 4,074 liters/hectare

With zinc 8.5 pounds/acre 5 gallons/1,000 sq. ft9.5 kilograms/hectare 2,037.3 liters/hectare

With zinc 15.5 pounds/acre 5 gallons/1 ,000 sq. ft17.4 kilograms/hectare 2,037.3 liters/hectare

With zinc 8.5 pounds/acre 10 gallons/1 ,000 sq. ft9.5 kilograms/hectare 4,074 liters/hectare

With zinc 15.5 pounds/acre 10 gallons/1 ,000 sq. ft17.4 kilograms/hectare 4,074 liters/hectare

Not treated

LSD

Population reduction %Weeks after initial treatment

6 10

45 27

33 28

34 13

52 48

35 11

59 42

30 19

82 78

-86 -96

112 117Note. Data are averaged over years (1999 and 2000) and locations.*The percentage of reduction in the moss population at six and 10 weeks was calculated by comparing the moss population per plot with the initial moss population.A pOSitive number denotes a decrease in moss population; a negative number denotes an increase in moss population.tAli treatments were applied at week zero and at two weeks after initial treatment.

Table 2. Effect of Daconil with and without zinc at various rates and spray volumes on percent reduction in silvery thread moss populations at Elk River Country Club, 1999-2000.

106 GeMMarch 2005

RESEARCH,-TJtE-RESEARCH!I says ...

~ Once a minor problem on golf courses, moss has increased in distribution and severity, probablybecause of changes in cultural practices and the discontinued use of mercury-based fungicides.

~ Adapted to a wide range of environments, mosses can survive dry, hot periods by becomingsemidormant and resuming growth when conditions are more favorable.

~ Mosses can reproduce through wind distribution of spores or transportation of small piecesof the plant by maintenance equipment or even golfers' shoes.

~ Fertilizers fortified with iron (Ironite and lronizer) and the chlorothalonil products DaconilWeather Stik and Daconil Zn all effectively reduced silvery thread moss.

Fred Yelverton, Ph.D. ([email protected]). is aprofessor and Extension specialist at North CarolinaState University, Raleigh, and co-director of the Centerfor Turfgrass Environmental Research and Education atN.C. State. He was an instructor at GCSAA'seducationconference at the GIS in Orlando.

levels of iron. HortScience 36:371-373.10. Yelverton, EH. 1998. Moss on bentgrass greens -

an increasing problem. Turfax 6(5):4.11. Yelverton, EH., IW. Rufty and K.D. Burnell. 2000.

Progress report: Management of silvery thread moss(Byrum argenteum) in bentgrass greens. ProgressReport to TCNC.January 2000.

Literature cited1. Danneberger, K., and J. Taylor. 1996. Moss on

greens: when the rolling stone stops. Golf CourseManagement 64(9):53-56.

2. Hummell, N.w., Jr. 1986. Factors influencing mossencroachment into golf course greens and its con-trol. Agronomy Abstracts 78:135.

3. Hummel, NW, Jr. 1988. Controlling moss ongolf course greens. Grounds Maintenance 23(1):82,130.

4. Hummel, NW, Jr. 1994. Methods for moss control.Golf Course Management 62(3): 106-109.

5. Lacey, W.S. 1969. Fossil bryophytes. BiologicalReviews 44:189-205.

6. Radko, A.M. 1985. Have we gone too far with lownitrogen on greens? USGA Green Section Record23(2):26-28

7. Richardson, D.H.S. 1981. The biology of mosses.Blackwell Scientific, Oxford.

8. Snow, J.I 1984. A rolling stone and healthy turf.USGA Green Section Record 22(6):7-9.

9. Xia, X., C.E Mancino and X. Xu. 2001. Annual blue-grass and creeping bentgrass response to varying

DACONIL VS. MOSS, JEFFERSON LANDINGDaconiltreatmentt Rate Volume

Without zinc 8.1 pounds/acre 5 gallons/1,OOO sq. ft.9.1 kilograms/hectare 2,037.3 liters/hectare

Without zinc 16.2 pounds/acre 5 gallons/1,000 sq. ft18.2 kilograms/hectare 2,037.3 liters/hectare

Without zinc 8.1 pounds/acre 10 gallons/1 ,000 sq. ft9.1 kilograms/hectare 4,074 liters/hectare

Without zinc 16.2 pounds/acre 10 gallons/1,OOO sq. ft18.2 kilograms/hectare 4,074 liters/hectare

With zinc 8.5 pounds/acre 5 gallons/1 ,000 sq. ft9.5 kilograms/hectare 2,037.3 liters/hectare

With zinc 15.5 pounds/acre 5 gallons/1 ,000 sq. ft17.4 kilograms/hectare 2,037.3 liters/hectare

With zinc 8.5 pounds/acre 10 gallons/1,OOO sq. ft9.5 kilograms/hectare 4,074 liters/hectare

With zinc 15.5 pounds/acre 10 gallons/1,OOO sq. ft17.4 kilograms/hectare 4,074 liters/hectare

Not treated

LSD

Population reduction (%)Weeks after initial treatment

6 10

79 80

91 90

86 87

91 96

78 85

81 84

91 90

91 89

68 25

20 21*The percentage of reduction in the moss population at six and 10 weeks was calculated by comparing the moss population per plot with the initial moss population.A positive number denotes a decrease in moss population; a negative number denotes an increase in moss population.tAli treatments were applied at week zero and at two weeks after initial treatment.

Table 3. Effect of Daconil with and without zinc at various rates and spray volumes on percent reduction in silvery thread moss populations at Jefferson Landing Golf Club, 1999.

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