Although still considered a minor nuisance, moss is becoming a more severe weed problem on an increasing number of putting greens throughout the temperate region. Present in many different habitats, the lack of economic importance has either encumbered or impeded extensive research on moss.
History and Characterization
Mosses are primitive plants that have changed little over the course of history. Fossil records date the appearance of moss 350 million years ago (Lacey, 1969). Moss is believed to have originated from filamentous (thread-like) green algae. Interestingly, moss and algae often share the same habitat and are often confused with each other. However, algae lack the leafy stems associated with moss and for the most part algae exist as individual cells or clusters of cells.
Mosses are classified as Bryophytes, which include the liverworts and hornworts. Within the mosses, approximately 15,000 species are classified into three groups. The first group is the granite mosses, which contain approximately 100 species. These mosses are primarily restricted to mountainous and arctic regions. The second group is the peat mosses which consist of roughly 350 species. Sphagnum is the important genus in this group, as it is added to soil mixes to enhance the soil's water holding capabilities. Each dead cell of sphagnum peat moss can hold up to 20 times its dry weight in water. The third group containing the true mosses, is the most pertinent to golf courses, and also the largest group with over 14,000 species. The true mosses can be divided into two major groups: tufted mosses which form on trees and rocks, and carpet-type mosses which are found on forest floors. In relatively dry conditions such as putting greens, the short, compact carpet mosses generally predominate (Birse, 1958).
Mosses differ structurally from higher plants, including turfgrasses, in that they are nonvascular (lack a phloem and xylem), have a very thin cuticle, and have no "true" roots, but do have structures called rhizoids that absorb water and nutrients. The lack of a vascular and root system restricts the size that the vast majority of mosses can grow. The moss species that inhabit a putting green may grow only to a millimeter or two in height. This is well below the acceptable mowing height for a creeping bentgrass, annual bluegrass, or bermudagrass putting green.
One difference between the life cycle of mosses and vascular plants is the production of spores (which requires free moisture for fertilization) by mosses, versus the production of seeds by vascular plants. Thus, Spanish moss is not a true moss because it produces seeds (it is related to the pineapple family).
Moss is difficult to control because it will grow in extreme situations where vascular plants including turfgrasses cannot. The most common areas most of us associate with moss, is heavily shaded moist environments. However, certain mosses can survive where moisture is lacking. Mosses are limited in the amount of moisture they can draw from rhizoids for metabolic requirements, and the need for free moisture for sexual reproduction, these constraints have resulted in mosses a) becoming aquatic b) being confined to continually moist habitats or c) evolving the ability to loose water almost as rapidly as its surrounding environment does and then resume metabolic processes as moisture returns (Richardson, 1981).
The mosses we faced in our studies typically survive extreme desiccation - and then upon remoistening, resume growth. One moss species we found in our studies, Bryum argenteum, is known to retain viability after 2 years of desiccation (Malta, 1921). The presence of moss may also be an indicator of a nutrient or chemical imbalance in the soil. Previous research has shown that mosses may be an indicator of Mg and Ca levels, and pH (Streeter, 1970). Generally moss has been reported to be associated with low pH's, but Hummel (1988) found that mosses were present on soils with a wide range of pH. Given the intensity of current golf green management that reduces the competitive ability of turfgrasses (lower mowing heights, reduced fertility, and modified soil mixes that may have chemical properties out of balance), moss will increasingly colonize these conditions (Radko, 1985).
Hummel (1988) cited factors that may encourage moss, which include: 1) potassium deficiencies 2) high calcium to magnesium ratio and 3) heavy soils. Past studies have identified that applications of ferrous sulfate, mercury based fungicides, lime, nitrogen fertilizers, and raising the mowing height as methods of moss control (Anonymous, 1985). Additionally, if moss invasion is small or limited to small areas, plugging is an effective control. With the elimination of the mercury based fungicides, current management practices that tend to stress creeping bentgrass on putting greens, and the increased occurrence of moss on sand based greens in our region, further studies are warranted.
Beginning with the statement, "Moss grows where other plants can't." Attempt to identify why moss is there in the first place. Check soil test reports for nutrient deficiency, and any soil layering especially on sand based greens that disrupts water flow. Minimize extreme management practices, fertilization, mowing, watering, cultural practices, etc. Listed below are a few more specific options for reducing moss.
Ferrous sulfate is a standard recommendation for moss control. At rates between 4 and 7 ounces/1000 sq.ft./month during the spring and fall we have found that ferrous sulfate turns the moss black with some reduction in population. In our studies moss tended to return after treatments stopped.
Hydrated lime in a few locations in the northeast United States have been observed to reduce moss populations. In our studies we have observed some modest reductions, but experienced phytotoxic affects with the product.
Soaps and salts
Dawn Ultra applications have reduced moss in our test studies. The applications have been made by mixing 10 ounces of Dawn Ultra in 2.5 gallons of water. The mixture is sprayed by hand onto the moss spots until saturation. Do not apply when the creeping bentgrass is under stress. It should be noted that this product is not labeled for moss control.
TerraCyte (sodium carbonate peroxyhydrate) is a granular product that is applied in the spring or fall. We have observed reduction in moss with TerraCyte. This product should not be applied when temperatures are high, and TerraCyte should be watered in immediately after application because some phytotoxicity can be observed.
Fungicides and Herbicides
Daconil Ultrex ® (chlorothalonil) is one of the most effective products for controlling algae. Regarding moss we have observed significant reduction of moss with repeated (biweekly) applications through the growing season. Most effective results are achieved when initiated early in the spring.
Junction ® (copper hydroxide) a turf fungicide contains copper hydroxide and mancozeb. The suggested program is 4 ounces/1000 sq.ft. applied weekly to biweekly starting in the fall. If application number exceeds 4 in one year monitor closely, because copper related toxicity issues may occur. This product has been effective in the northeast and through the mid-Atlantic region, but may cause injury to creeping bentgrass in the southeastern United States.
Quicksilver® (carfentrazone) a herbicide is effective for moss control, specifically the silvery thread moss. Usually 2 to 3 sequential applications will give good moss control. Applications should be made when creeping bentgrass is not under stress.
Caution: In all cases when using products labeled for moss follow labeled instructions. In other cases, be sure to test out moss control strategies in small test areas.
Anonymous. 1985. And where did all this moss come from? USGA Green Section Record 23(2):30.
Birse, E. M. 1958. Ecological studies on growth-form in bryophytes. J. Ecol. 46:9-27.
Hummel, N.W. 1988. Controlling moss on golf course greens. Grounds Maintenance 23(1):82,130.
Lacey, W.S. 1969. Fossil bryophytes. Biol. Rev. 44:189-205.
Malta, N. 1921. Acta Univ. Latv. 1:125-129.
Miller, R.H. and J.F. Wilkinson. 1977. Nature of the organic coating on sand grains of nonwettable golf greens. Soil Sci. Soc. Am. J. 41:1203-1204.
Radko, A.M. 1985. Have we gone too far with low nitrogen on greens? USGA Green Section Record 23(2):26-28.
Richardson, D.H.S. 1981. The Biology of Mosses. Blackwell Scientific Publications. Oxford. Streeter, D.T. 1970. Bryophyte ecology. Sci. Prog. Oxford 58:419-434. Authors: Karl Danneberger
Copyright OSU Buckeye Turf Program. Website manager: Dr. Tim Rhodus