Reed sweet grass
Also known as
Glyceria, swamp grass, water meadow grass, Poa aquatica
Where is it originally from?
What does it look like?
Aggressive, perennial, mat-forming grass (<1.9 m tall) with fibrous roots and rhizomes and an erect or lax stem. Soft, light green leaves (30-60 x 2 cm) have a membranous ligule. Much-branched flowerhead has numerous spikelets containing many seeds.
Why is it weedy?
Forms a dense monoculture in nutrient-rich bogs and water. Matures quickly, has a rapid growth rate, and overtops competitors. Sets many long-lived seeds, and rhizomes spread outwards, breaking off and rooting in any damp spot. Tolerates damage, grazing and pollutants, but doesn't like heavy frost and shade.
How does it spread?
Seed and rhizome fragments spread by flowing water. Contaminated diggers, livestock, soil movement, dumped vegetation, eel nets, boats and trailers all spread seed and rhizome fragments into new catchments, pasture, and drains.
What damage does it do?
Forms dense mats on water and in damp areas, replacing most other species and degrading the habitat for native flora and fauna. Causes silt accumulation and flooding, and attracts cattle into wetlands, causing further degradation of the area.
Which habitats is it likely to invade?
Wetlands, bogs, freshwater margins, lakes, and streams in open frost-free areas.
What can I do to get rid of it?
Begin all control work at the top of the catchment, and minimise site disturbance and the creation of bared areas.
1. Spray (spring to autumn): glyphosate (10ml/L + penetrant). If valuable species are at risk of spray contact, use 520g/L haloxyfop-P-methyl (5ml/L + crop oil). Resource consent may be required to spray over water .
2. Machine dig all year round. Dispose of fragments at refuse transfer station, dry out and burn, or bury. Follow up with limited spraying.
3. Weedmat: difficult to apply, need to cover all of infestation to avoid rhizome survival and leave covered 3-4 months
What can I do to stop it coming back?
Follow up controlled areas regularly as rhizomes resprout and the seed bank can reinfest bared sites.