Black grass, blackgrass, Gerard’s rush, mud rush, saltmarsh rush, saltmeadow rush, Juncus gerardi Loisel., Juncus gerardii var. gerardii Loisel., Juncus gerardii var. pedicellatus Fernald

Juncus gerardii is easy to confuse with J. compressus, another non-native species in the Great Lakes (Online Atlas of British & Irish Flora 2012).

Seedling recruitment occurs in dry, uncovered areas where there is little competition for light (Bertness 1991 in Charpentier et al. 1998, Keddy and Ellis 1985 in Charpentier et al. 1998). Shoot emergence usually begins in March and ends in June, when water becomes a limiting factor (Bouzillé et al. 1997). Fertile shoots tend to grow taller than vegetative shoots (Bouzillé et al. 1997). Juncus gerardii typically flowers and produces fruit from May to August (Lady Bird Johnson Wildflower Center 2012).

Communities of J. gerardii expand by vegetative rhizomal growth, forming clonal populations (de Kroon and Schieving 1990 in Bouzillé et al. 1997). Growth and expansion of clonal populations of J. gerardii is not deterred by temporary cold spells, and initial research indicates that cold spells may be for stimulation of flowering (Bouzillé et al. 1997).

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

Environmental	Socioeconomic	Beneficial

Juncus gerardii has a moderate environmental impact in the Great Lakes.

Juncus gerardii cannot invade areas with existing vegetation or dense litter (Ericson 1981 in Jutila 1999). Juncus gerardii seedlings also have little resistance to burial by wrack (floating plant material); significant amounts can lead to burial and ultimately seedling death (Brewer et al. 1998). For these reasons, J. gerardii becomes established in the first stages of succession after a disturbance (Bouzillé et al. 1997)

Juncus gerardii poses a competitive threat to the native and naturalized Juncus spp. in the Great Lakes, especially those listed as threatened or endangered, including J. alpinus auct. non Vill., J. ambiguus Guss., J. balticus Willd., J. biflorus Elliot, J. marginatus Rostk. var. biflorus (Elliot) Alph. Wood, J. brachycarpus Engelm., J. brachycephalus (Engelm.) Buchenau, J. dichotomus Elliot, J. diffusissimus Buckley, J. ensifolius Wikstr., J. greenei Oakes & Tuck., J. interior Wiegand, J. militaris Bigelow, J. pelocarpus E. Mey., J. scirpoides Lam., J. secundus P. Beauv. ex Poir., J. stygius L., J. stygius L. ssp. americanus (Buchenau) Hultén, J. subcaudatus (Engelm.) Coville & S.F. Blake, and J. vaseyi Engelm. (USDA NRCS 2012c).

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

Many Juncus spp. serve as a host for larvae of Coquillettidia, a genus of mosquitoes that can serve as a vector for various animal- and human-borne diseases (Sérandour et al. 2010).

The vegetative parts of J. gerardii are round, stiff, and sharp enough to puncture human skin (College of Environment 2012).

Juncus gerardii may be confused with or pose a competitive threat to native rushes that are culturally important, including J. arcticus ssp. littoralis and J. effusus (USDA NRCS 2012b).

Juncus gerardii has a moderate benefit in the Great Lakes.

In the native portion of its range, J. gerardii is often a preferred species for restoration (especially post-Phragmites control) because its lower growth forms a more open landscape (Casagrande 1997).

Numerous animals feed on the seeds of rushes, including waterfowl, songbirds, quail, cottontail, muskrat (also feeds on roots and rhizomes), porcupine, and other small mammals (Martin 1951 in Stevens and Hoag 2003).

Juncus spp. provide habitat for amphibians and various wetland birds, as well as spawning ground for some fish species (Stevens and Hoag 2003).

The dense root and rhizome system of Juncus spp. enable them to survive periods of stress (drought, flood, etc.), accumulate soil, and provide erosion control (Stevens and Hoag 2003).

Cattle, horses, and sheep will graze on Juncus spp., but J. gerardii’s specific value as fodder is unknown (Centre for Aquatic Plant Management 2004, Cosyns et al. 2005).

The rhizome matrix can support numerous bacteria that can be useful in wastewater treatment (Stevens and Hoag 2003).  Use of the plant has been explored for phytoremediation of cadmium (Podlipná et al 2011), boron (Türker et al 2016) and other heavy metals (Milic et al 2021).

Phenanthrenes isolated from J. gerardii have been examined for cytotoxicity against cancer (Stefkó et al 2020) and the plant has also been investigated as a source of antioxidants (Grigore & Oprica 2015)

Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species.

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

Control
Juncus gerardii seedlings that emerge in late winter or early spring are taller and fertile and can be distinguished from the seedlings that emerge at the end of spring or beginning of summer and are shorter and infertile (Bouzillé et al. 1997).

Biological
Aphids may occasionally feed on Juncus spp., but most rushes are fairly resilient to extensive damage from insect or diseases (Stevens and Hoag 2003). Cattle, horses, and sheep graze on Juncus spp., but the extent of control gained from grazing is unknown (Centre for Aquatic Plant Management 2004, Cosyns et al. 2005).

Physical
There are no known physical control methods for this species.

The rhizome matrix of Juncus spp. enables it to withstand periods of drought and flooding; water level fluctuation is not recommend as a physical control method (Stevens and Hoag 2003).

Efforts made to graze an area with J. gerardii may increase the size of its seed bank (Jutila 1999; Jutila 1998).

Chemical
Sethoxydim will target most grass species and should not affect nearby broadleaf herbs, sedges, or woody plants (IPAW 2012). Glyphosate and ammonium salt of imazapyr will control J. gerardii, but are non-selective and should be applied carefully (Centre for Aquatic Plant Management 2004). Glyphosate should be sprayed directly onto foliage in mid-late summer (Centre for Aquatic Plant Management 2004).

Other
Charpentier et al. (1998) found that a water depth of 10 cm and salinity level of 2 g/L NaCl caused J. gerardii to stop shoot and root growth and decrease seed production. A constant water level and a low salinity level may limit the growth and expansion of J. gerardii populations (Charpentier et al. 1998).

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