Salvinia (Salvinia molesta)

Salvinia is a floating water weed with oval-shaped leaves that have many waxy hairs on the top of the leaf. It forms dense mats that take over waterways and reduces water quality.

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How does this weed affect you?

Salvinia forms dense mats that can smother the surface of the water. It:

  • prevents native water plants from growing
  • reduces food and habitat for fish and other aquatic animals
  • causes stagnant water and unpleasant odours
  • provides habitat for mosquitoes to breed
  • reduces or prevents the use of waterways for recreation and transport
  • interferes with floodgates and other river management structures
  • reduces the visual appeal of waterways.

What does it look like?

Salvinia is a fast growing floating water fern. 

Leaves (fronds):

  • are round-to-oval
  • grow in opposite pairs
  • have many waxy hairs on the upper surface
  • are light green (or yellowish in low nutrient water)

Leaves have three growth stages:

  1. Primary stage: leaves are less than 15 mm wide and float flat on the water.
  2. Secondary stage: leaves are 20 - 50 mm wide and slightly cupped with only the lower surface of the leaf in the water.
  3. Tertiary stage: leaves are up to 60 mm wide tightly folded and plants are densely packed together.

Stems are:

  • green
  • covered with fine hairs
  • slender
  • submerged
  • branched with nodes develop roots.  

Roots are:

  • hairy and trailing from stem nodes
  • up to 25 cm long

Spore sacs are on stalks among the root-like filaments but they do not produce spores in Australia.

Where is it found?

Salvinia grows along the NSW coast. It is common in the Tweed, Richmond, Clarence, and Macleay catchments, the central coast and Sydney metropolitan areas. There are heavy infestations in the Hawkesbury–Nepean system and in Woolombi Brook near Cessnock. 

There are also infestations on the South coast of NSW.

 It has been sold illegally as an aquarium plant and sometimes found in aquariums and fishponds.

What type of environment does it grow in?

Salvinia is a perennial plant that is very adaptable and survives in many climates and nutrient levels. It grows best in warm fresh water that is still or slow-flowing and has high nutrient levels.

It can double in size in less than 3 days in ideal conditions. Rain can also stimulate growth by washing nutrients into the water.

Salvinia can survive: 

  • low temperatures and occasional frosts if there is a thick mat to protect some plants (exposed parts of the plant will be killed by frost)
  • brackish water although sea water will kill it
  • dry periods as the thick mat can protect the buds.

Maps and records

  • Recorded presence of Salvinia during property inspections (Map: Biosecurity Information System - Weeds, 2017-2020)
    These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.

  • Estimated distribution of Salvinia in NSW (Map: NSW Noxious Weed Local Control Authorities, 2010)
    Map shows weed distribution and density estimated by local council weeds officers in 2010.

How does it spread?

By plant parts

Salvinia can produce by plant parts in two ways:

  • Plant fragments - If a part of the stem containing a node breaks away from the main plant it can grow a new plant. Damaged or dead plant material stimulates bud development. One pair of leaves can start an entire new infestation.
  • Daughter plants - Mature plants produce buds at the join between sections of the stem and these develop to form daughter plants. 

Salvinia spreads to new areas by:

  • attaching to boats, trailers and vehicles
  • human activities such as keeping it in fishponds or aquaria and inappropriate disposal of the plant 
  • attaching to animals such as water birds, turtles or cattle.

Once in a waterway the plants can be spread by

  • water flows especially floods
  • wind.

By spores

The spores are not viable in Australia

More information

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Control

Successful weed control requires follow up after the initial efforts. This means looking for and killing regrowth or new plants. Using a combination of control methods is usually more successful.

To tackle salvinia:

  • seek advice from a local council on the best control strategies for your situation
  • act quickly to control new infestations.

Booms and nets

Floating booms or nets on waterways can help contain salvinia and limit spread to other areas.  The plants that have been collected behind the booms are then easily controlled with chemicals or mechanically removed.

Water management

Reduce nutrient levels in waterways by:

  • managing erosion on cultivated land
  • controlling stock access to banks and waterways
  • diverting effluent before it enters the waterway
  • not washing waste from cattle yards or dairies into waterways.

Physical removal

Remove all plant parts to prevent rapid re-growth. Contact your local council for advice on how to dispose of this weed.

By machine

Mechanical removal is expensive and only an option for small infestations.

Biological control

Salvinia can be effectively controlled with the Salvinia weevil (Cyrtobagous salviniae). The adult salvinia weevil is a small, black insect which grows to about 2 mm long. Adult weevils feed on the growing tips, suppressing growth. Larvae tunnel through the horizontal stems, particularly in younger parts of the plant causing the weed to break apart, sink and decompose on the bottom of the waterway. 

The level of control depends on the local climate and the condition of the salvinia plants. When conditions are ideal the weevil can complete its life cycle in six weeks. On the North Coast of NSW in nutrient rich water it has controlled infestations within six months. Though in other areas it may take 2-3 years for weevil populations to establish. 

The weevil does most damage when salvinia is healthy and green and the temperature is around 30°C. Weevils breed very slowly at temperatures less than 20 °C and ceases breeding below about 17 °C.

The best time to introduce the weevil is early spring. The warmer weather helps populations establish. If an infestation is multi-layered or old, pull out some of the weed or strip spray with herbicide.

Contact your local weeds officer to find out more about introducing salvinia beetle in your area.

Chemical control

Chemical control requires good access to the weed in waterways. It is best to control the infestation early. Dense, mature infestations are difficult to control with herbicides. The densely-folded and compact leaves make it difficult to get good herbicide contact.

Reedy banks and swampy backwater areas protect the plant from herbicides. Salvinia can rapidly reinfest these sites.

Herbicide options

WARNING - ALWAYS READ THE LABEL
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 www.apvma.gov.au

See Using herbicides for more information.


PERMIT 83083 Expires 31/03/2022
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: Nil.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate


PERMIT 14327 Expires 30/06/2022
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: 1 L in 100 L of water
Comments: Hand gun application, follow directions on the permit
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


Diquat 200 g/L (Reglone®)
Rate: 400 mL per 100 L of water
Comments: Spot spray to wet all foliage thoroughly, add Agral 600. 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


Diquat 200 g/L (Reglone®)
Rate: 5.0–10.0 L/ha
Comments: Boom spray to wet all foliage thoroughly, add Agral 600. 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 (Water Clear®)
Rate: 1.0 L per 100 L of 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 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.
All of NSW Prohibition on dealings
Must not be imported into the State or sold
Central West Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
Greater Sydney
Exclusion zone: whole region except for the core infestation area of the Georges and Hawkesbury-Nepean Rivers and their tributaries.
Regional Recommended Measure*
Whole region: Land managers mitigate the risk of the plant being introduced to their land. Exclusion zone: The plant is eradicated and the land kept free of the plant. The Local Control Authority should be notified if the plant is found. Core infestation area: Land managers should prevent spread from their land where feasible.
Hunter Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. Land managers should mitigate spread from their land. The plant should not be bought, sold, grown, carried or released into the environment. Land managers reduce impacts from the plant on priority assets.
This Regional Recommended Measure applies to Salvinia molesta and Salvinia minima
Murray Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
North West Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. Plant should not be bought, sold, grown, carried or released into the environment.
Riverina Regional Recommended Measure*
Land managers should mitigate the risk of the plant being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant.
South East Regional Recommended Measure*
Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW DPI Biosecurity Helpline on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2020