Spotlight on Moss

By Pam Sherratt

Moss is a small, non-vascular, flowerless plant in the taxonomic division Bryophyta (Figure 1). Being non-vascular means that mosses lack xylem and phloem, the vascular systems that transport water and nutrients in higher plants. Instead, they rely on simpler tissues for water conduction. While some mosses have slightly more advanced structures, their water-conducting tissues are not lignified, preventing them from growing as tall as other plants. Mosses absorb moisture and nutrients through their leaf-like structures (phyllids), with water and nutrients moving from cell to cell by osmosis. Like other plants, they photosynthesize. However, they reproduce using spores instead of seeds and do not produce flowers. Their spores are dispersed by wind. Mosses also lack true roots, instead using small hair-like structures called rhizoids to anchor themselves to surfaces.

There are over 12,000 species of moss, displaying a wide variety of morphologies and habitats. Mosses can thrive in nearly all ecosystems, enduring both extreme heat and cold, as well as wet and dry conditions (some are even aquatic). As some of the oldest land plants, they are found worldwide—everywhere except in saltwater environments.

In the turfgrass industry, mosses commonly appear in shaded and wet conditions, such as on lawns and grounds. The most frequently encountered species in closely mowed turf, particularly on golf course greens, is silvery thread moss (Bryum argenteum).

Like most weeds, moss will fill in gaps and take over the turfgrass sward when conditions favor its growth over turf. This is particularly common in shaded and wet areas. Turfgrasses adapted to shade, such as tall and fine fescues, can better compete with moss in these environments. Additionally, improving drainage in shaded areas is crucial, as they tend to retain moisture longer and often suffer from poor air circulation.

Other factors that encourage moss growth include:

• Mowing height: Low-cut or scalped turf is more susceptible.
• Fertility: Excessive applications of soluble nitrogen, particularly from spoon-feeding.
• Irrigation: Overwatering, especially in areas with poor drainage.
• Soil compaction: Compacted soil reduces surface drainage, creating unfavorable conditions for turfgrass.

Moss is difficult to control once established, so prevention is the best approach. A well-planned turfgrass management program that promotes healthy turf growth is the most effective defense against moss and other weeds. If moss is present, it's essential to identify the environmental factors favoring its growth and address them to achieve long-term control.

In high-cut turf areas, such as lawns, moss can often be removed manually using a metal leaf rake, with the debris taken off-site to prevent vegetative spread.

However, moss on low-cut turf, such as putting greens, presents a greater challenge. In his research, Dr. Zane Raudenbush observed that silvery thread moss can thrive even in well-managed greens with a sound integrated pest management (IPM) program. While it requires water to survive, it uses very little and actually benefits from frequent irrigation. Older moss colonies are particularly difficult to control, as their rhizoids extend deeper into the soil, making removal more challenging.

In some cases, applying a herbicide may be the best option. Quicksilver (carfentrazone-ethyl) is a contact herbicide labeled for silvery thread moss control in golf course turf. Since it is a contact herbicide, it will injure the moss (though the affected moss remains in place as it slowly decomposes), but it will not completely kill it, as moss is a perennial plant. A two-pronged approach is most effective: applying the herbicide in conjunction with cultural practices such as aerification, topdressing, and overseeding to promote healthy turf growth and prevent moss from re-establishing. Flushing patches of silvery thread moss with detergent is another effective way to injure the moss. A typical rate is 2 oz of detergent per 1 gallon of water, which weakens the moss enough for those areas to be re-seeded with desirable turf species.

Moss is a persistent challenge in turfgrass management, particularly in shaded and wet environments. Prevention through sound cultural practices is key. When moss appears, identifying and correcting the underlying environmental conditions is essential for long-term control. For severe infestations, integrating herbicide applications with aerification and overseeding can help restore turfgrass dominance.

Pam Sherratt is a Turfgrass Specialist in the Department of Horticulture at The Ohio State University.