Reed manna grass

Glyceria maxima

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Identification

Appearance

Glyceria maxima is a perennial, semi-aquatic, rhizomatous grass. Stems are unbranched and can reach 2-8.2 feet in height.

Foliage

Leaves are 12-23.6 inches long, 0.2-0.8 inches wide, with an acute apex and a prominent midrib. The leaf margins have stiff, short hairs. The leaf sheaths are rough in texture with a reddish-brown band at the leaf junction.

Flowers

Flowering occurs from June through August, when flowers appear in 6-12 inches long open panicles. The panicle branches have short, stiff hairs like those on the leaf margins.

Fruit

The small seeds are 0.06-0.08 inches long, obovoid in shape and smooth in texture. This plant reproduces primarily vegetatively through rhizomes.

Biology

ECOLOGICAL THREAT

Glyceria maxima occurs in sunny to semi-shady wetlands, where it can form dense impenetrable monocultures that crowd out native species. It is native to northern Eurasia and was first found in North America in 1940 on the edge of Lake Ontario.

ORIGIN

The first specimen of Glyceria maxima in North America dates from 1940 and comes from a marsh at the edge of Lake Ontario. Between 1940 and 1952 several more populations of the plant were located in this same region. It is possible that Glyceria maxima arrived some time before these records were documented. It may have been introduced intentionally as a forage species, or accidentally as part of packing material. The first record of Glyceria maxima in New England comes from the Ipswich River Wildlife Sanctuary in Essex County, Massachusetts in 1990. This Massachusetts population appears to be under control, and has provided some initial insights into how the species can be held in check.

HABITAT

River banks, stream banks, open wetlands, shoreland, disturbed areas

LIFE CYCLE

This species primarily reproduces vegetatively via rhizomes in North America. Reed mannagrass emerges early in the year and concentrates up to 50% of its biomass in its root system. The energy stored in the roots and rhizomes enable this species to produce new shoots through the growing season.

Glyceria maxima also has florets that can bloom and produce viable seed. Individuals are in bloom between June and August. Once the inflorescences are mature, the panicle opens and rises above the other foliage. Seeds dispersed in the fall will likely germinate the following spring; however, seeds can remain dormant and viable in the soil for several years.

During the winter, reed mannagrass becomes dormant. In early spring, regrowth occurs from rhizomes buds.

Management Options

This is considered a watch list species

MECHANICAL MANAGEMENT

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. Small infestations of G. maxima can be dug up; care should be taken to remove all parts of the roots and rhizomes. Subsequent removal of seedlings germinated from the seed bank or missed rhizomes pieces may be necessary.

The vegetative spread of larger populations can be controlled by repeated mowing, cutting, harvesting, roto-tilling, or rotovating.Where applicable, these treatment methods can be supplemented with artificially created flood conditions.

CHEMICAL MANAGEMENT

Be careful not to damage or kill nearby native plants when conducting management work.
Always read and follow pesticide label directions. Application of pesticides may require a certification from the Agency of Agriculture, Food and Markets. The Agency website provides information on what applicator certification is needed.

A foliar spray of glyphosate (3% solution) applied early to late summer will control populations of G. maxima. Follow up for several years. Rhizomes may survive after initial spraying.

In floating fens in the Netherlands, sulfate was experimentally added to the soil. This caused the free sulfide concentration to increase and resulted in a decrease in the growth of G. maxima.

For large populations, herbicide treatment will be an effective option. If the decaying plant material falls into a nearby body of water and decomposes, the dissolved oxygen levels could decrease. To avoid this, dead plant material should be removed two to four weeks after herbicides have been applied.