Agrostis alba auct. Non. L., Agrostis alba var. alba, Agrostis alba var. gigantea, Agrostis stolonifera var. major (Gaudin) Farw, Agrostis stolonifera var. gigantea, Agrostis palustris Huds., Agrostis depressa Vassey, Agrostis nigra, carpet bentgrass

Redtop can be distinguished from other Agrostis spp. bentgrasses) by its colorful inflorescence during the blooming period and the width of its leaf blades (up to 1/3" across). Other bentgrasses have an inflorescence that is green or grey during the blooming period and their leaf blades are narrower. Some spikelets of redtop are located near the rachis (central stalk) of the inflorescence; the spikelets of other bentgrasses are often more remote from the rachis. In general, bentgrasses can be distinguished from other grasses by their tiny one-flowered spikelets and their keeled persistent glumes, which lack conspicuous tufts of hair.

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental

Current research on the environmental impact of Agrostis gigantea in the Great Lakes is inadequate to support proper assessment.

Potential:
Nationwide (U.S.), A. gigantea is considered to be a medium to low-impact nonnative plant species based on documented ecological impacts and widespread distribution (Natureserve 2010). It exhibits aggressive reproductive characters and is reportedly very competitive with native species (Natureserve 2008). Agrostis gigantea should not be introduced if native revegetation is sought (Tilley et al. 2010).

While redtop can provide a new food source for some grazers, Dugger et al. (2004) found that rabbit density was lower in redtop-dominated habitat relative to natural areas with taller and denser vegetation, probably due to relatively reduced cover and food availability in redtop areas. Elk may use redtop as a food source in the spring (Tilley et al. 2010); however, one foraging study of introduced Rocky Mountain elk (Cervus elaphsu nelsoni) in the French River region (Ontario) suggested that A. gigantea is not a significant forage species for elk populations in the Great Lakes region (Jost et al. 1999).

There is little or no evidence to support that Agrostis gigantea has significant socio-economic impacts in the Great Lakes.

Current research on the beneficial effect of Agrostis gigantea in the Great Lakes is inadequate to support proper assessment.

Potential:
Historically, redtop was a significant forage producer in hay pastures. However, its agricultural use declined as more palatable species such as timothy (Phleum pretense) and Kentucky bluegrass (Poa pratensis) became popular and as soybean crops began replacing hay pastures (Carey 1995).

Agrostis gigantea can inhabit wet, acidic sites and has a notable tolerance for concentrations of some heavy metals (e.g., copper and aluminum) in the soil; it has thus been used to rehabilitate disturbed sites, such as eroded stream banks and abandoned mines (Carey 1995, McLean and Gilbert 1927, Paschke and Redente 2002). Redtop was considered for use in animal waste treatment after laboratory experiments found this plant to be a relatively effective purification agent, reducing total phosphorous and ammonium-nitrogen concentrations in nutrient-rich water (Takada-Oikawa 2006). It has also been evaluated as a high-quality sustainable turf species for Wisconsin and Illinois (Diesburg et al. 1997).
Agrostis gigantea could provide good cover for upland birds and waterfowl, such as ducks and geese (Tilley et al. 2010). Redwing blackbirds (Agelaius phoeniceus) appeared to utilize redtop-dominated habitat as much as oak-planted habitat, although taller and denser vegetation was preferred overall (Furey and Burhans 2006).

Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species. However, the Michigan Department of Natural Resources (MIDNR and MIDEQ 2009) recommends use of redtop for erosion control in forested land. Moreover, redtop’s close cousin, creeping bentgrass (A. stolonifera), is commonly put to commercial use on golf course putting greens, tees, and fairway turf (Banks et al. 2004).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Biological
There are no known biological control methods for this species.

Physical
This species has rhizomal roots that can grow to a depth of four feet (Tilley et al. 2010), making mechanical removal of redtop difficult, time-consuming, and unlikely to be successful, as any significant portions of the rhizome that are not removed from the soil could generate new plants.

Continuous grazing or mowing to a height of less than three inches may result in temporary control (Tilley et al. 2010).

Chemical
Due to the tendency for this species to form dense, monospecific turfs (Tilley et al. 2010) herbicide application should be easy to manage. Increased grass chlorosis (yellowing of the plant due to reduced chlorophyll production) results when herbicides are applied during cool weather (10°C) (McCullough and Hart 2006).

Among available herbicides, redtop is very susceptible to atrazine (Carey 1995). It can also be well controlled by glyphosate. However, glyphosate-resistant strains of the related creeping bentgrass (A. stolonifera) do exist and are becoming more common (Hart et al. 2005); commercial release is likely to increase the potential for unintended transfer of the herbicide resistance gene to A. gigantea (NatureServe 2008).

Given the ease of hybridization with other Agrostis species (Tilley et al. 2010), if control methods listed above are not successful, alternative chemical control methods may also be considered. For instance, in tests conducted in Virginia, the closely related creeping bentgrass experienced at least a 92% die-off after applying isoxaflutole, imazaquin, or mesotrione in two to three sequential applications (Beam et al. 2006). Fluazifop-P has also been effective in controlling bentgrass species (Hart et al. 2005). In addition, creeping bentgrass seems to be susceptible to rimsulfuron, especially when the herbicide is kept dry after application (Barker et al. 2005).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.