Parrots feather
Haloragaceae - Myriophyllum aquaticum
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What does it look like?

Parrot's feather is a submerged, bottom-rooted perennial aquatic herb.  The top 10cm of foliage can be emergent, standing above the water. Sprawling foliage is pale grey-green, and stems are up to 2m long.  Leaves are finely divided, feathery, and arranged in whorls of 4-6.  Emergent and submerged leaves differ in form.  It flowers from September – February.  Only female plants are present in New Zealand so no seed is set. 

Still or slow moving water bodies including wetlands, lakes, streams, rivers, drains and ponds to a depth of approximately 5+m.  It is unlikely to be severely problematic in large exposed lakes.  Tolerates slightly brackish conditions.  Favours water bodies with high nutrient (especially nitrogen) and light levels.  Tolerates fluctuating water levels, including complete exposure of sediment.  Growth rates increase in response to increases in carbon dioxide.  May benefit from climate change.

Why is it a problem?

History of invasiveness overseas.  Taller growing form than native Myriophyllum species.  Rapid growth rate and highly variable growth forms. Allelopathic - releases chemicals that affect the growth of other species.  Growth from fragments provides competitive advantage in dynamic environments.

Does not set seed in New Zealand.  Grows from small fragments.

Control Methods

Freshwater weeds are difficult to eradicate once established, but are possible to control. Before you start thooughly check the waterway's adjacent areas and inflows to see if the infestation has spread.

As most aquatic weeds grow from fragments, start control at the upstream end of the infestation. In narrow waterways you can reduce the growth of aquatic weeds with riparian planting to reduce light levels.

Small infestations

  • Physical control: Remove the weeds by digging and raking them up. Dispose of them on land so they dry up and die. Follow up regularly to remove growth.
  • Bottom lining (small ponds): If possible, lower the water level and cover the infestation with black polythene or weedmat (weighted down) for about three months.

Large infestations

  • Herbicide: These are available for some freshwater weeds, and can be an effective control option. Check with your local council's biosecurity team before spraying, as spraying in or over water may require resource consent. CAUTION: When using herbicide, PLEASE READ THE LABEL THOROUGHLY and follow ALL instructions and safety requierments.
  • Biological control: Grass carp can be used as a weed controll agent in some cases. This requires a permit - contact the Department of Conservation for more information.

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