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Tall manna grass

(Glyceria maxima)

Photo of tall manna grass
Photo credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Semi-aquatic, perennial grass with unbranched stems that get up to 8’ tall. Reddish tint on the lower parts of the stems.

Overview

Other names for this plant include:
  • Common names: reed sweetgrass, reed manna grass, English water grass
  • Scientific names: G. aquatica; G. spectabilis; Molinia maxima; Panicularia aquatica
Ecological threat:
  • Tall manna grass invades wetlands, including swamps, lakes, ponds, slow-moving rivers, creeks, ditches and wet pastures, where it forms monospecific stands that are capable of crowding out native vegetation.
  • It degrades wetland habitats because it is not suitable for nesting and is a poor food source for wildlife.
  • Tall manna grass has been sold as an ornamental in a variegated variety.
  • Young shoots can cause cyanide poisoning in cattle if used as forage.
 Overview map of tall manna grass classification in WI
Prohibited (red) and restricted (orange) counties

Classification in Wisconsin: Prohibited/Restricted (Restricted in Brown, Calumet, Columbia, Dane, Dodge, Door, Fond du Lac, Green, Jefferson, Kenosha, Kewaunee, Manitowoc, Milwaukee, Outagamie, Ozaukee, Racine, Rock, Sheboygan, Walworth, Washington, Waukesha and Winnebago counties; Prohibited elsewhere)

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for tall manna grass was based upon this literature review [PDF] developed by the department.

Identification

Leaves: Leaves protrude at an angle from the white base, with broad, flat, rough-edged blades, but strongly “V” shaped at their base. Leaf-sheaths fused inches below juncture with a blade (in wetlands unique to Glyceria grasses).

Flowers: Erect, sturdy panicle with spikelets several-flowered (1-2.5 mm wide). Spikelet ovate, 5 to 10 mm long with lateral compression. Lemmas with conspicuously raised veins, awnless and upper glumes with 1 vein.

Fruits & seeds: Seeds are dark brown (1.5 to 2 mm long)

Stems: Unbranched up to 8 feet tall. Often lays down and appears shorter. 5-10 leaves per stem.

Roots: Rhizomes

Similar species: Glyceria grandis is shorter (to 5 feet); has smooth leaf edges; a weak, nodding panicle; 4 to 6 mm spikelets, and only 3-6 leaves per stem.

Distribution

See the reported locations of tall manna grass in Wisconsin.

Do you know of additional populations? Send us a report.

Control

Mechanical: If feasible, black plastic can be used to smother the infested area; cutting plants several times throughout the year can also effective at limiting root reserves but may take a long time to kill the grass. Flooding can also be an effective method when the grass is cut.

Chemical: 3% solution of glyphosate in early and late summer. Follow up for several years.

Photos

View tall manna grass pictures in our photo gallery!

Resources

Sources for content: Links for more information: