Coastal Invasive Species Committee

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Giant Mannagrass

Glyceria maxima

giant_mannagrass

ERADICATE

Family: Poaceae (Grass).

Other Common Names: Reed mannagrass, reed sweetgrass.

Origin: Europe and temperate Asia.

Growth Form/Reproduction: Rhizomatous perennial grass. Seeds and rhizomes.

Legal Status: None.

Impacts:
Agricultural: Introduced as forage for grazing animals on seasonally inundated pasture. Cyanide poisoning of cattle can occur when animals graze young shoots. Dense stands can create drainage problems.
Ecological: Tall dense single-species stands in wetlands can affect native plant diversity and reduce wildlife food sources and habitat.
Human: No information available.

Habitat: Adapted to wet, nutrient-rich soil in full sun but tolerates light shade. Tolerates wide range of water levels. Seeds require bare, exposed soils to colonize. Lakes, watercourses, wetlands, banks of slow-moving rivers.

Status and Distribution: Rare in the Capital and Cowichan Valley Regional Districts. Not known elsewhere in the CIPC area.

Management Strategy: Individual plants can be excavated but all rhizomes must be removed; follow up treatment is usually necessary. Small populations can be cut, then covered with black plastic. Repeated cutting may reduce vigor of giant mannagrass while giving lower-growing plants a competitive advantage. Foliar spray of glyphosate can provide effective control.