(Glyceria maxima - Poa aquatica)

Glyceria Flower1 

What is glyceria?

  • Glyceria is a troublesome weed of farm dams, creeks, ponds and rivers in Tasmania.

How to identify glyceria

  • Glyceria is a perennial (long-lived) aquatic grass.
  • The leaves of glyceria are shiny, hairless and mid-green in colour, and grow 30-60 cm above the water surface. The leaves end in an abrupt point and the edges are rough to touch as the finger is drawn from tip down to the base.
  • Glyceria produces an extensive root system to a depth of approximately one metre. It also forms a sprawling mat of rhizomes (underground stems) which produce vast numbers of shoots which can quickly expand the size of the plant.
  • Glyceria produces a branched inflorescence (or spike of flowers) in spring and summer, comprising a large number of spikelets that range from yellow to green in colour, with a purplish tinge.
  • Glyceria stops growth at the onset of winter. Growth recommences in spring with a flush of new shoots from the rhizomes.
  • For help in identifying glyceria, search the Dennis Morris Weeds and Endemic Flora Database for glyceria illustrations. If you are still in doubt about the weed you are dealing with, contact Biosecurity Tasmania on 03 6165 3777 for help.
Glyceria Flower Glyceria - Dam
Image top & above left: Glyceria in flower, © K Fenner.
Image above right: Glyceria infestation in dam, © K Fenner.

Glyceria in Tasmania

  • Glyceria is not declared in Tasmania.
  • Glyceria is found throughout Tasmania.
  • Glyceria occurs in rivers, creeks, dams, drains and other waterways with depths of up to two metres. In deeper waterways it sometimes forms vast floating mats which remain attached to the bank.
  • Glyceria infestations have also established on a number of roadsides in the absence of permanent standing water.
  • Dense stands of glyceria can reduce the holding capacity and access areas of dams and waterways.
  • In rivers, creeks, and irrigation and drainage channels, glyceria can restrict and even block water flow. Destruction of the weed can also result in a large amount of decaying vegetation polluting the water and blocking pump intakes, channels and ditches.
  • Glyceria accumulates toxic levels of hydrocyanic acid which has resulted in cattle deaths from cyanide poisoning.

What you need to do

If you locate glyceria anywhere in Tasmania, or if you find a plant that you think could be glyceria, immediately contact Biosecurity Tasmania on 03 6165 3777 to report this weed.

Detailed management and control guidelines for glyceria can be found in the Glyceria Control Guide. Refer also to Herbicides for Glyceria Control. For further information see Weed Links and Resources.

See also
Herbicides for Glyceria Control
Weed Links and Resources

Other useful links
Pest Genie

Glyceria Control Guide


  • Plan your control program, this will save time and money in the long-run;
  • Consider a non-herbicide method first;
  • Consider the impact of your control methods on off-target species, especially if herbicides are used;
  • Ensure machinery and equipment is washed down between sites or prior to contractors leaving site;
  • Get in early - For new infestations, eradicate before the plants reach the flowering stage: once plants begin seeding, control becomes more difficult and expensive;
  • Carefully time your use of herbicide for best results (see Herbicides for Glyceria Control for more information);
  • Coordinate your control program with neighbouring landholders where your weed problem crosses property boundaries; and
  • Revisit and regularly inspect the site and ensure follow-up is undertaken;


  • Don't start your control program without first planning your approach;
  • Don't allow an infestation to become established. Get in early!
  • Don't rely on just one treatment: follow-up is essential.

Spread of glyceria

  • Glyceria produces vast numbers of seeds throughout summer and autumn. Some seeds germinate immediately, whilst others remain dormant for several years.
  • Seed may be spread on water, in mud on machinery and vehicles, on footwear and on livestock. Glyceria seed is not readily spread by wind.
  • Germination generally occurs in spring, with seedlings quickly developing an extensive mat of roots and rhizomes throughout summer and autumn. These rhizomes give rise to vegetative shoots in the first year, and both vegetative and flowering shoots in subsequent years.
  • Glyceria can also be spread by small fragments of rhizome being moved around in mud on machinery and implements.

Avoid the introduction of glyceria

  • Thoroughly clean any equipment that comes into contact with glyceria or the soil of infested areas.

Physical removal

  • Small plants can be easily removed from damp soil by hand-pulling. Use a spade when hand removal is more difficult.
  • Make sure you remove all pieces of the roots and rhizomes, otherwise the plant can quickly regrow.
  • Large plants are difficult to completely remove using machinery as roots and rhizomes may be missed during excavation.
  • Use mechanical removal to reduce the size of large infestations, allowing easier follow up by manual removal of small plants and regrowths.
  • Excavated material should be dumped well away from the area at a suitable site where it can dry out and kill all plants.
  • Mechanical excavation avoids herbicide residues left in the water as well as decomposition of dead plant material in the water. The capacity of the storage may also be increased by excavation.
  • Be careful using heavy equipment near waterways to avoid damage to the structure of the waterway.


  • If low water levels permit, an alternative to excavation is to cultivate the area in autumn.
  • Cultivation brings root and rhizome material to the surface to dry out. This method gives good control of small infestations, and can reduce the size of large infestations to manageable levels.
  • Take care to thoroughly clean all machinery after cultivation, to reduce the risk of spreading rhizome material.

Chemical control

  • A limited number of herbicides are registered for use on glyceria in Tasmania due to problems with off-target effects on rivers. See Herbicides for Glyceria Control for more information.
  • Using a herbicide has several disadvantages. The mass of decaying vegetation reduces a dam's holding capacity and can allow invasion by other weeds or a re-invasion of glyceria.
  • Use of a backhoe, bulldozer or dragline may be needed to restore the dam to its original capacity.
  • Decomposition of the dead plant material can render the water unfit for use by stock.

Herbicides for Glyceria Control

Herbicides for Glyceria Control

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