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.
Azolla is found in slow moving and stationary waterways, and at least one species is found in each state and territory.
Azolla produces spores and can spread by fragments.
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
See Using herbicides for more information.
Diquat 200 g/L
Rate: 5.0–10.0 L/ha
Comments: Spray to wet all foliage thoroughly. Observe withholding period.
Withholding period: 1 day in pasture, 10 days in treated water.
Herbicide group: L, Inhibitors of photosynthesis at photosystem I (PSI inhibitors)
Resistance risk: Moderate
Orange oil 55.2 g/kg
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
Azolla (Azolla species) is not declared in NSW under the Noxious Weeds Act 1993.