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Tall manna grass

Tall manna grass (Glyceria maxima)

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

Overview

Regulated areas of tall manna grass
Tall manna grass is Prohibited (Red counties)/Restricted (Orange counties)

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.

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 developed by the department.

Identification

Leaves: Blades are flat or slightly folded and ¾” wide and 8-12” long. Leaf blades are shallowly grooved, have a prominent mid-rib and leaf margins have stiff short hairs. Leaf sheaths are rough and have a red-brown band at junction with leaf. Ligules are 0.2” long.

Flowers: The inflorescence is an open panicle 6-12” long with branches that have short stiff hairs. Spikelets are 0.2-0.3” long with florets that are tinged greenish-purple. Blooms June-August.

Fruits & seeds: Seeds are small, smooth, dark brown, and are 0.07” long and ovoid in shape. They also have a deep, narrow central furrow.

Roots: Rhizomes

Similar species: American mannagrass (Glyceria grandis; native) is typically up to 4.5’ tall and has a nodding inflorescence with shorter spikelets.

Distribution

Known county distribution of tall manna grass
Counties in WI where tall manna grass has been reported (as of July 2011). Both vouchered and unvouchered reports included.

Do you have tall manna grass in your county but it isn't shaded on the map? 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 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

Last revised: Wednesday July 20 2016