Controlling moss in putting greens

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               This work was partly funded by the Oregon GCSA.                                          SCIENCE FOR THE GOLF COURSE
                                                                                                       d e d i c at ed to en rich ing t he e nv i ron ment of g olf

Controlling moss
in putting greens
Extensive testing shows that some products control moss infestation to
some 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 on
putting greens has prompted four years of
research on a wide range of chemical
control strategies. Although this research
remains a work in progress, it has
revealed a great deal about what works
and what doesn’t and about moss growth
in putting greens. Here we outline current
control strategies and point out areas of
future research.

Biology and ecology
of putting green moss
    Of approximately 20 species of moss
found in association with turf in temperate
climates, Bryum argenteum, or silvery
thread moss, is the species most com-
monly associated with putting greens. In
nature, B. argenteum is found from sea               Bryum argenteum, the moss most commonly associated with putting greens,differs in appearance from common lawn mosses.
level to timberline and from the Arctic to
Antarctica. It is common in cold and tem-
perate climates but rare in tropical ones.
Cosmopolitan and ubiquitous, it colonizes                                                                         not a vascular plant and has no roots. It is
disturbed, often dry sites and generally is                 KEY points                                            anchored by rhizoids, which resemble
considered a pioneering species. It is                                More Info:                    roots but do not appear to function in
often part of the early succession on sand                                                                        uptake of water or nutrients. Without
                                                           Bryum argenteum, or silvery thread                     xylem and phloem, it has no means to
dunes, bare rock and gravelly soil. Along
                                                              moss,has become a common pest                       translocate foliar-absorbed nutrients. Like
with a small number of other mosses, it is
                                                              on putting greens.                                  other mosses associated with turf, B.
well adapted to human-altered environ-                     Products containing copper hydrox-
ments, including sand-based putting                                                                               argenteum reproduces via spores pro-
                                                              ide, iron and fatty acids have all
greens and push-up greens that have                                                                               duced in distinctive capsules and by plant
                                                              shown some ability to control moss
been topdressed regularly with sand.                                                                              fragments likely spread during mowing
                                                              in putting greens.
Unlike many mosses, it grows well in both                                                                         and other cultural practices such as cor-
                                                           A drastic change in cultural practices
wet, shady environments and hot, dry                          may be the best defense against                     ing. To date, we have not observed spore
sites in full sun.                                            moss infestations.                                  capsules on moss growing in putting turf.
    Like most bryophytes, B. argenteum is                                                                            The current prevalence of moss in

putting greens probably reflects recent
trends in putting green culture, including
extremely low mowing, minimal nitrogen
fertilizer, increased use of sand growing
mediums, intense sand topdressing and
loss of mercury fungicides, which were
highly toxic to moss. It occurs on both
bentgrass and Poa annua greens but is
by far a bigger problem on sand-based
bentgrass greens. We have found sig-
nificant populations on first-year greens
on new golf courses. It often shows up
first in weak areas such as ridges and
mounds where grass is thin because of
scalping or drought stress. It aggres-
sively colonizes low, wet areas and
thrives on soil-based greens with shallow
layers of sand built up by topdressing.

Research strategies                          Relative residual moss control in plots treated the previous winter with junction ( Copper Hydroxide + Mancozeb),No-Mas
    Our research, conducted at Oregon (fatty acid soas),daconil fungicide,and an untreated check plot.
State University, primarily concerns moss
growing in creeping bentgrass greens,
and the following results are from work         caused severe turf injury at rates neces- Advanced screening
done entirely on Providence creeping sary for moss kill. Caused root stunting in                                  The next phase involved further test-
bentgrass in sand-based growing medi-           turf.                                                         ing of products that showed promise for
ums and SR 7200 velvet bentgrass grow-               Copper soaps. Copper soaps are not moss control and caused little or no turf
ing on soil and topdressed with sand. To labeled for moss control. We found them injury. Products included ferrous and fer-
date we have concentrated on large-scale to be highly effective moss killers but toxic ric sulfate, fatty acid soaps and copper
broadcast treatments rather than spot                                                                         hydroxide products. All of these have
                                                to turf, even at moderate rates.
treatments directed at localized infesta-                                                                     been tested repeatedly at several rates
                                                     Zinc sulfate. These products are not
tions. Most of the chemical treatments
                                                labeled for moss control in putting greens, and with varying numbers of repeat appli-
have been applied during fall and winter
                                                although some retail products are labeled cations. Research results for these prod-
when temperatures range from 40 to 65 F                                                                       ucts are summarized below.
                                                for moss control in lawns. Acceptable
and moisture from precipitation is com-                                                                       Iron products
                                                moss control but caused significant turf
mon. Soil pH in the area is typically 5.5 to                                                                      Normal rates of iron for turf color
                                                injury at marginally high rates.
6.5, and salt levels are very low.                                                                            enhancement are about 0.03 pound
                                                     Daconil Zn and Daconil Ultrex. Both
                                                products are labeled as fungicides and                        iron/1,000 square feet. Under cool, wet
Early screening trials                          not for moss control. They were ineffec-                      conditions, rates of 0.15 to 0.20 pound
    After unsuccessful attempts by super- tive in controlling moss under low-tem-                             iron/1,000 square feet controlled moss
intendents to try iron products at normal       perature conditions. Some reports                             marginally without injury or blackening of
putting green rates, we screened a wide indicate control at higher summer tem-                                Providence creeping bentgrass turf.
range of products by applying each at a         peratures. No undesirable side effects on                     Ferric sulfate is more effective at killing
variety of rates from low to very high. turf even after 15 repeat treatments.                                 moss than ferrous sulfate, but both
Products included in our experiments                 Dawn Ultra. Dawn Ultra was ineffec-                      require a series of five to seven treat-
were selected because reports in the liter- tive on moss at rates ranging from 2 to 8                         ments applied at two-week intervals. Turf
ature indicated that they controlled moss or ounces of product/1,000 square feet                              is exceptionally dark green during treat-
that they were being applied on putting         when applied during cool, wet conditions. ment. We achieved up to 90 percent
greens in an attempt to control moss. We Dawn Ultra is marketed as a dishwashing                              moss control with both ferrous and ferric
eliminated products that caused turf dam- liquid, and certified commercial pesticide                          sulfate, which is encouraging but not as
age and others that had no effect on the applicators                                            cannot        effective as we would like. Annual appli-
moss. The following products were tested legally apply Dawn Ultra for moss control. cations may be necessary, and control is
and eliminated from consideration.              Doing so would be the same as applying                        not always consistent. Field test results
    Copper sulfate. Copper sulfate is not       an unregistered pesticide.                                    have been mixed, with most tests using
labeled for moss control. In our tests, it                                                                    ferrous sulfate and reporting fair to good

control.                                      sis developed the second year.                              and thus increase the chance of turf
                                              Symptoms were worse on weak or                              loss during the summer.
Copper hydroxide products                     shaded greens. Greens in full sun were
    Most of our research has used Kocide      not affected. We concluded that the                            Superintendents who have used
2000, which is straight copper hydroxide,     symptoms were not phytotoxicity but iron                    copper hydroxide products have
and Junction, which contains both copper      chlorosis. Further experiments in which                     reported mixed field results. In western
hydroxide and mancozeb fungicide. Both        we alternated copper treatments with                        Oregon and Washington and parts of
products show similar activity and are        0.05 pound iron/1,000 square feet during                    California, superintendents have
registered for moss control.                  a sequence eliminated signs of chloro-                      reported excellent and fairly long-lasting
    In western Oregon, we achieved effec-     sis.                                                        control without deleterious effects to
tive moss control with five to seven treat-                                                               turf. Other superintendents have
ments applied at two-week intervals at        Current recommendations                                     reported short-term or partial control,
rates of 0.1 to 0.15 pound copper/1,000           Current recommendations are to                          and in parts of California, some have
square feet during cool wet weather           apply copper hydroxide products during                      reported no control at all. Factors that
between October and March. Moss injury        cool weather at 0.10-0.15 pound cop-                        may affect control are lack of extended
occurs gradually and is progressively         per/1,000 square feet at two-week inter-                    periods of cool temperatures, low-
greater with each application. A minimum      vals for a total of five to seven                           humidity environments, high soil and
of five treatments is needed to prevent the   applications. If signs of iron chlorosis                    water pH, and elevated salt levels in irri-
moss from growing back. We normally           occur during or after treatment with cop-                   gation and/or spray solutions. Copper
plan on six to seven treatments. During       per hydroxide, apply iron at 0.05 pound                     may not be effective in these situations,
treatment turf darkens slightly but not as    iron/1,000 square feet as needed to                         but further research is clearly needed.
dramatically as with iron products.           eliminate chlorosis. Iron can be tank-
Darkening continues into the spring even      mixed with copper hydroxide if constant                     Fatty-acid soaps
after treatments have been completed. A       agitation is maintained in the spray solu-                      Soap products have been used for
single treatment series of seven applica-     tion. A minimum spray volume of 2 gal-                      many years for lawn moss control, and
tions has provided one to two years of        lons/1,000 square feet is suggested.                        anecdotal reports of control with prod-
acceptable moss control in our local                                                                      ucts such as Dawn Ultra detergent,
area.                                             Please note: In areas with hot, stress-                 which is not labeled as a pesticide,
                                              ful summers where summer root loss is                       prompted evaluation of soap products
Potential problems                            common, conduct thorough on-site test-                      for use on putting greens. We screened
    Using copper hydroxide for moss           ing on nursery turf to make sure copper                     several products based on fatty acids,
control raises several concerns. One is       treatments do not cause root stunting                       all of which were effective in killing
the potential buildup of copper in the root
zone, which may stunt root growth. In
early screening trials, applying the equiv-
alent of 6 pounds of copper/1,000
square feet over a one-year period
stunted root growth. Although this is four
to seven times the amount that would be
applied in a normal treatment sequence,                  Copper-induced Iron Chlorosis
it is still cause for concern. We now
advise applying copper treatments no
more than two years in a row at a total
rate of 1.0 pound copper/1,000 square
feet/year. However, surface soil levels of
copper as high as 42 ppm have been
noted without any apparent root stunting
under our climate conditions.
    Copper-induced iron chlorosis is
another concern with copper hydroxide
products. The problem was first
observed where copper treatments had
been applied on golf courses for two
consecutive years. No problems
                                              Relative residual moss control in plots treated the previous winter with Junction ( Copper Hydroxide + Mancozeb),No-
occurred the first year, but severe chloro-   Mas (fatty acid soap),Daconil fungicide,and an untreated check plot.

                                                                                                                                                     GCM     105
moss. Since initial screening, we have        the Pacific Northwest, we generally
concentrated on one product recently                                                        during cool weather in sequential applications ha
                                              expect residual control during the grow-
registered as No-Mas, which is a 22                                                         been                                         almo
                                              ing season after treatment. Long-term
percent active formulation of a fatty-acid                                                  as effective, and fatty-acid soap products sho
                                              control is not as good as for copper-
salt.                                                                                       great promise. All treatments have side effects th
                                              treated plots, and it appears annual
    Testing soap products differs from                                                      must be considered. Treatments discussed in th
                                              treatments will be required.
testing common pesticides because                                                           paper are not effective in some areas of the cou
the amount of water applied as a car-                                                       try, and regional research is needed to fine-tu
                                              Potential problems
rier profoundly affects the optimal rate                                                    treatment programs.
                                                 Problems we have encountered
of active ingredient. At a given rate of                                                                       Acknowledgments
                                              include excessive phytotoxicity when              Partial funding for this research has been pro
active      ingredient,       phytotoxicity   soap applications are followed by frost.      vided by the Northwest Turfgrass Association, th
increases as the total volume of spray        Poa annua appears to be more sensitive        Oregon GCSA and Griffin LLC. Thanks to Illahe
solution decreases. After much testing,       than Providence creeping bentgrass            Hills Country Club and superintendent B
                                                                                            Swancutt, and Trysting Tree Golf Club and Pa
we established a rate of 0.63 gallon of       under these conditions. Occasionally turf     Doran, CGCS, for allowing us to use their facilitie
product/1,000 square feet applied in a        scorching has occurred even when              for field testing. Appreciation is also extended t
minimum of 6 gallons of spray solu-           treatments have been applied under            numerous undergraduate students in horticultur
tion/1,000 square feet. The same rate                                                       for assistance in maintaining research plots.
                                              optimal conditions of mild rainy weather.
applied in 12 gallons of spray solu-          Rinsing treated plots within an hour of
tion/1,000 square feet is probably opti-      soap application will generally minimize                          References
mal for maximum moss control without          turf scorching. Turf scorch from soap         1. Cook, T., and B. McDonald. 2002. Controllin
turf injury, but it is virtually impossible                                                    moss in putting greens. Turfgrass Managemen
                                              applications is similar to a light tip burn      in the Pacific Northwest 5(1):4-6.
to achieve with most spray systems.           from soluble fertilizer applications. Turf    2. Happ, K.E. 1998. Moss eradication in puttin
                                              recovery is generally very rapid.                green turf. USGA Green Section Reco
    Note: There are many soap products                                                         36(5):1-5.
                                              Thoroughly test soap products on site         3. Hummel, N.W., Jr. 1988. Cultural and chemica
on the market registered for general          before using in wide-scale spray pro-            strategies for controlling moss (Bryum argen
moss control. They vary greatly in con-       grams.                                           teum) in creeping bentgrass. Agronom
centration and recommended dilution                                                            Abstracts 80 (Nov./Dec.):152.
rates. Be sure to study specific product                                                    4. Schofield, W.B. 1992. Some common mosse
                                              Summary                                          of British Columbia. Royal British Columbi
labels carefully to avoid inadvertent turf        At some point assessing the impact           Museum, Victoria, British Columbia, Canada.
injury.                                       of cultural practices on moss encroach-
                                              ment becomes important. The starvation
    Our research indicates that two           theory of putting green maintenance has
applications applied two weeks apart          been followed to the point where in
generally achieve a high level of con-        some cases the turf is gone and only the
trol. Moss kill is rapid and appears as       moss remains. Growing a dense healthy
a pronounced bleaching of moss                stand of turf is still the best way to pre-
accompanied by a slight lightening of         vent moss from dominating turf.
turf. Turf lightening increases with          Superintendents should experiment with                               Tom Cook, M.S.
each      subsequent        application.      ways to generate green speed other            (, is an assoc
Alternating soap applications with iron                                                             ate professor of horticulture; Brian
                                              than starving turf to the point of thinning     McDonald is a research assistant, in the
applications at 0.05 pound iron/1,000         and mowing so low that adequate den-                  horticulture department; and Kathy
square feet maintains turf color and                                                         Merrifield, M.S., is a senior research assis
                                              sity cannot be maintained. As long as          tant in the department of botany and plan
darkens the dead moss, improving the          current trends in turf management con-          p a t h o l o g y, all at Oregon State University,
overall appearance of the turf. Iron                                                                                   Corvallis.
                                              tinue, moss problems will persist.
applications can be made to soap-                 Once moss invades putting greens,
treated plots the day following soap          foolproof control is impossible. The
application. Iron will precipitate out        treatment approaches described in this
and clog spray nozzles if it is mixed         paper have provided acceptable moss
with the soap solution.                       control in the environmental conditions
    Soap treatments have been gener-          of the Pacific Northwest. According to
ally effective in western Oregon and          our results, the most effective products
Washington. Reports from research in          include copper hydroxide products
California indicate poor control with win-    applied during cool weather in sequen-
ter applications in an arid environment       tial applications. Iron products applied
with high pH water and high pH soils. In


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