Verdure: Don't let moss be the boss

Researchers at the University of Guelph (Ontario) investigated the possible influence of irrigation rate and frequency on moss in creeping bentgrass.


Filed to: Verdure, moss

Publilius Syrus (85-43 B.C.) was a writer in ancient Rome credited with the proverb “a rolling stone gathers no moss.”  Mosses are small, flowerless plants known as bryophytes. These plants lack true leaves or stems, but their “leafy-like” tissues are green and contain chloroplasts for photosynthesis. They also absorb water and nutrients through their “leaves.” They don’t have roots, but rhizoids help anchor them in place.

Mosses also are nonvascular plants, which means they don’t have the “internal plumbing” system of xylem or phloem. Since mosses are flowerless, they don’t produce seeds, but reproduce by spores.

Moss first appeared on land 470 million years ago. Today there are about 12,000 species of moss; the most common on golf course putting greens is silvery thread moss (STM; Bryum argenteum). STM is especially invasive in putting greens of wet and shaded environments, and it likes to occupy voids caused by scalping and pitch marks.

Chemical control of moss is limited since it lacks a vascular system to absorb and translocate a herbicide. Therefore, researchers at the University of Guelph (Ontario) investigated the possible influence of irrigation rate and frequency on moss in creeping bentgrass. A survey of golf courses in southwestern Ontario revealed that STM was the species found on greens, and therefore greenhouse experiments were conducted using STM.

To establish simulated putting greens in the greenhouse, plastic circular pots of 3-inch diameter by 15-inch depth (7.5 centimeters by 38 centimeters) were prepared with a USGA-specification sand root zone. Total surface area for each pot was 5.1 square inches (33 square centimeters) and seeded with Penn A4 creeping bentgrass for the first experiment and L-93 creeping bentgrass for the second experiment. For both experiments, the turfgrass was seeded and established, fertilized weekly and maintained at 0.20-inch (5-millimeter) height-of-cut.

For both experiments, STM was obtained from a golf course in the Ontario area, ground into a fine powder and inoculated into each pot. All pots were irrigated with deionized water at either 75% or 100% evapotranspiration (ET) replacement measured from an open evaporation pan and irrigated every day, every two days, four days or seven days. These irrigation treatments (two amounts and four timings) were applied over a three-month period, and all treatments were arranged in the greenhouse in four replications. At the end of each experiment, STM fresh weight from each pot was measured to compare irrigation treatments.

What were the results? Irrigation quantity (75% or 100% ET replacement) had no effect on the presence of STM. Irrigation frequency did influence STM: Watering every day or every two days favored STM invasion and persistence, with significantly much less STM encroachment when watered every four or seven days. Thus, irrigation frequency — and not the amount of water — is an important factor in the establishment and competitiveness of STM in a creeping bentgrass putting green.

Also, creeping bentgrass roots were examined at the conclusion of the experiments. Regardless of irrigation amount, significantly more root mass was measured at four- and seven-day irrigation timings compared to watering every one to two days. Therefore, on putting greens, by increasing moisture in the root zone and reducing moisture at the surface, creeping bentgrass is healthier and more competitive than moss.

While moss is an unwelcome invader of putting greens, it is encouraged in Japanese gardens to add a sense of calm and stillness to the site. Moss is used with bonsai — the art of growing and training miniature trees in small pots — to cover the soil and provide an impression of old age. With regard to moss and putting greens, Publilius Syrus also said, “Observation, not old age, brings wisdom.”

Source:  Lyons, E.M., K.S. Jordan, I.T. James, D.M. Hudner and D. McGowan. 2012. Irrigation frequency influences establishment of silvery thread moss (Bryum argenteum Hedw.) and rooting of creeping bentgrass (Agrostis stolonifera L.) on simulated golf greens. Acta Agriculturae Scandinavica, Section B – Soil and Plant Science 62 (sup1):79-85 (

Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 20-year member of GCSAA.