Reed sweet grass
Poaceae - Glyceria maxima

What does it look like?

Erect clumping perennial grass, reaching almost 2m tall.  Leaves are up to 2cm wide.  Creeping rhizomes, can form mats that are attached at the bank but floating in deeper water.  Flowers spring-summer; flower heads are up to 45cm long, branched, with spikelets yellow-green with purple tinge.  Seeds small, dark brown, summer-autumn.

Still and slow-moving eutrophic water bodies including wetlands, streams and drains, in water up to approximately 1-1.5m deep.  It doesn’t tolerate heavy frost or full shade, but will grow in light shade.  Positively associated with soil nitrogen and phosphorous.  Prefers silt and other soft substrates.  Temperate climate species.

Why is it a problem?

History of invasiveness overseas.  High variation in responsiveness to nutrient availability compared to New Zealand native sedges, facilitating rapid biomass accumulation and competitive advantage under high nutrient conditions.  Grazing tolerant, but spread can be accelerated by release of grazing pressure.  Less competitive under dense, woody vegetation.

Reproduces by seeds (prolific) and rhizomes.

Control Methods

Begin all control work at the top of the catchment, and minimise site disturbance and the creation of bared areas.

Physical control

  • Machine dig all year round. Dispose of fragments at refuse transfer station, dry out and burn, or bury. Follow up with limited spraying.

Herbicide control

  • Weed wipe (spring-autumn): glyphosate (200ml/L + penetrant).
  • Spray (spring to autumn): glyphosate (10ml/L+ penetrant). If valuable species are at risk of spray contact, use Gallant NF (5ml/L + 5ml crop oil). Resource consent may be required to spray over water .
  • Weedmat: difficult to apply, need to cover all of infestation to avoid rhizome survival and leave covered 3-4 months.

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