Azolla (Azolla species)

Azolla is an aquatic, free-floating Australian native fern that occurs in many waterbodies.


How does this weed affect you?

Azolla is an Australian native fern that is common in many waterways and is commonly used as a decorative feature in garden ponds. It supports a nitrogen-fixing cyanobacterium in its fronds. This nitrogen is released when the plants decay.  It can quickly spread to cover open areas of water and may build up in stationary water bodies, particularly if nutrients levels are adequate.

Azolla is often grown in paddy fields in Asia as a fertiliser.

Where is it found?

Azolla is found in slow moving and stationary waterways, and at least one species is found in each state and territory.

How does it spread?

Azolla produces spores and can spread by fragments.

What does it look like?

Azolla is a free-floating fern, 1–2.5 cm in diameter. The leaves are tiny, scale-like and 2-lobed (lobes 0.2 cm long). Older leaves can be red in sunlight and green in the shade. The main stem has pinnate branches, and branches are longer towards the base of the stem giving the plant a triangular shape.

Azolla filiculoides does not have fine rootlets. Azolla pinnata does have fine rootlets.

Similar looking species include: salvinia (Salvinia molesta) in its primary growth stage, and duckweed (Lemna spp. and Spirodela spp.).


Compiled by Jessica Grantley, Fiona McPherson and Andrew Petroeschevsky

Edited by Matthew Stevens and Elissa van Oosterhout

More information

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Herbicide options

Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website

See Using herbicides for more information.

PERMIT 83083 Expires 30/04/2025
Carfentrazone-ethyl 240 g/L (Shark™ Aquatic Herbicide)
Rate: 933 mL of product per ha
Comments: DO NOT apply more than two (2) applications per year with a minimum re-treatment interval of 90 days between consecutive treatments.
Withholding period: Not required when used as directed.
Herbicide group: 14 (previously group G), Inhibition of protoporphyrinogen oxidase (PPO inhibitors)
Resistance risk: Moderate

Diquat 200 g/L (Reglone®)
Rate: 5.0–10.0 L/ha
Comments: Spray to wet all foliage thoroughly. Observe withholding period.
Withholding period: Do not use treated water for human consumption, livestock watering or irrigation purposes for 10 days after application. Do not graze or cut sprayed vegetation for stock food for 1 day after application. See label for harvest withholding periods.
Herbicide group: 22 (previously group L), Inhibition of photosynthesis at photosystem I via electron diversion (PSI electron diversion)
Resistance risk: Moderate

Orange oil 55.2 g/kg (Water Clear®)
Rate: 1 part product per 100 parts water
Comments: Spray on to free-floating plants.
Withholding period: Nil.
Herbicide group: n/a
Resistance risk: n/a

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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area Duty
All of NSW General Biosecurity Duty
All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.

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For technical advice and assistance with identification please contact your local council weeds officer.

Reviewed 2018