Controlling Moss in Creeping
Bentgrass Putting Greens

Brian McDonald*, Alexander Prideaux**, and Tom Cook***

Horticulture Department
Oregon State University
Corvallis, Oregon


For several years we have been screening chemicals to determine their effectiveness in selectively killing moss in putting greens. Our goal has been to develop a strategy that will allow us to effectively kill the moss without injuring the grass. Our general approach has been to apply repeated applications of either metal compounds (ie. Copper Hydroxide, Copper Sulfate, Ferrous Sulfate, Ferric Sulfate, Zinc Sulfate, etc.), soap compounds (eg. HO2), metal soap compounds (eg. NEU 1140), or Fungicides (Daconil Zn, Daconil Ultrex, Junction). So far we have determined approximate rates of application, optimum timing of applications, approximate number applications required, and side effects on bentgrass turf from continued applications over time. This report summarizes what we have learned overall from numerous trials we have conducted. Preliminary results from trials conducted during the last winter and spring seasons follow this report.


Key Findings 1998-2000:


Chemicals SUITABLE for moss control:

Ferrous and Ferric Sulfate
Copper Hydroxide Products
Copper Hydroxide + Mancozeb
HO2 (Fatty Acid Salts)

Chemicals that need more testing:

NEU 1140 (Copper Soap)

Chemicals NOT suited for moss control:

Copper Sulfate - injures turf
Zinc Sulfate - injures turf
Daconil Zn & Ultrex - no moss kill
Dawn Ultra Detergent - no moss kill


Optimum rates & number of treatments:

Ferrous Sulfate - 0.2 lb Fe/1000 applied 5- 7 times at two-week intervals.
Ferric Sulfate - 0.2 lb Fe/1000 applied 5-7 times at two-week intervals.
Copper Hydroxide - 0.1-0.2 lb Cu/1000 applied 5-7 times at two-week intervals.
Copper Hydroxide + Mancozeb - 0.1-0.2 lb Cu/1000 applied 5-7 times at two-week intervals.
HO2 - 15-20 oz ai/1000 applied 3 times at two week intervals.

Optimum timing of treatments:

All of our work has been done between October and late May under cool weather conditions. Experience with iron products at high rates in hot weather indicates turf injury is likely. We have not tried copper during summer weather conditions. We have not tried the fatty acid products in summer but I would expect to see turf injury at that time at rates used in our trials.

Side effects on grass:

At normal rates (0.1-0.2 lb Cu/1000/application) with a maximum of 7 applications in any 12 month period, turf shows a slight darkening response that lingers through summer.

Heavy application rates (10-15 repeats of copper hydroxide at rates above 0.2 lb Cu/1000/application) applied several years in a row have resulted in weak bentgrass turf that shows mottled chlorosis in summer, persistent drought stress symptoms, and generally poor turf quality.

Recent field observations on putting greens that are weak due to shade, poor drainage, and/or poor air movement indicate copper toxicity occurring with as few as 4 applications. This yellow chlorosis looks exactly like Iron chlorosis and appears to be induced by high tissue levels of Copper. Greens in full sun have not shown these symptoms. Limited research indicates coring and supplemental Iron applications may eliminate these symptoms. We are currently studying this phenomena.

Typical Iron application rates for moss control (0.1-0.2 lb Fe/1000/application) turn turf very dark green during the treatment period. Color enhancement does not last into summer.

HO2 causes a slight lightening of the turf color with each application. Color can be restored with Iron applications applied a few days after the HO2 treatments.


Other factors being investigated:

The optimum spray volume of HO2 and NEU 1140 has not been determined. Our trials have utilized spray volumes of 12 gal/1000, which is very high by normal standards. Our efforts in the coming cool season will attempt to determine the lowest effective spray volume that will still control moss.

The effectiveness of alternating treatment strategies over time needs to be evaluated. To avoid potential buildup of Copper in soil from long term repeated treatments, we will look at the effectiveness of using Copper one year, Iron the next, and Soap the next.

We will also look at alternating Soap and Iron treatments during a given treatment period to maintain grass color and minimize the lightening associated with Soap treatments.



HO2 has a label but the product is not yet in commerce in the USA. The label rate calls for 0.63 gal of product per 1000 sq. ft applied in a minimum of 12 gal of water per 1000 sq. ft. Three applications at two-week intervals are recommended.

Junction is in the process of receiving a new label including moss on greens. The label calls for 7 applications applied at two-week intervals starting sometime between mid November and finishing before May. Proposed rates are 4-6 oz of product per 1000 sq ft per application. All of our work has been done on bentgrass so I canšt make a knowledgeable recommendation for use on annual bluegrass at this time.


* Brian McDonald is a Research Assistant in the OSU Horticulture Dept.

** Alexander Prideaux is recent graduate of the Turf Program at OSU.

*** Tom Cook is associate professor of Horticulture at Oregon State University