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
• reduces water quality, causes stagnant water and unpleasant odours
• provides habitat for mosquitoes to breed
• reduces or prevents the use of waterways for recreation and transport
• blocks irrigation channels and equipment
• interferes with floodgates
• 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.

Similar looking plants

At the primary growth stage salvinia looks like:

• Azolla (Azolla spp.), which have alternate leaves.
• Duckweeds (Lemna spp. and Spirodela spp.).

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, 2017-2023)
  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.
  
  

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 and wind.

By spores

The spores are not viable in Australia

More information

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Control

Successful weed control relies on 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

See Using herbicides for more information.

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PERMIT 83083 Expires 30/04/2025
Carfentrazone-ethyl 240 g/L (Shark™ Aquatic Herbicide)
Rate: 933 mL of product per ha
Comments: For nonflowing water bodies. DO NOT apply more than two (2) applications per year with a minimum re-treatment interval of 90 days between consecutive treatments. See permit for further critical use comments.
Withholding period: Not required when used as directed.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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PERMIT 14327 Expires 31/07/2026
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: 1 L in 100 L of water OR 6 - 9 L / Ha
Comments: Hand gun application. Use of this permit is limited to staff and contractors of NPWS and agencies/ organisations represented by Regional Weed Committees. See permit for further critical use comments.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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Diquat 200 g/L (Reglone®)
Rate: 400 mL per 100 L of water plus 150 mL Agral / 100 L water
Comments: Spray to wet all foliage thoroughly. About 1 mL of product should ne sufficient to treat 1 metre squared of weeds.
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: L, Inhibitors of photosynthesis at photosystem I (PSI inhibitors)
Resistance risk: Moderate

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Diquat 200 g/L (Reglone®)
Rate: 5.0–10.0 L/ha
Comments: Apply as overall spray wetting foliage thoroughly. Use higher rates for heavy infestations or for deep or dirty water. Oxygen depletion of decaying weeds may occur therefore do not spray more than a quarter of the area at any one time.
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: L, Inhibitors of photosynthesis at photosystem I (PSI inhibitors)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: 1 tablet for every 37.5 cubic metres of water to achieve 400 parts per billion.
Comments: For use on dense or established weed populations in enclosed water bodies, deeper than 0.5 m and larger than 37.5 cubic metres, or margins of larger, still water bodies. Throw tablets directly into the water to achieve uniform distribution of the herbicide. See label for further instructions and restrictions.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: Inject solution into water body. 1 tablet per 37.5 cubic metres. Each tablet dissolved in at least 20 L of water + 0.5-1.0% adjuvant/surfactant
Comments: For use on dense or established weeds in water bodies less than 0.5 m deep or with a volume less than 37.5 cubic metres. Dissolve tablets in water (at least 20L per tablet) mix thoroughly and then inject the solution directly into the water body.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: Spray 12 - 15 L of solution per 100 m2. Solution = 1 tablet per 100 L water + 0.5-1.0% adjuvant/surfactant.
Comments: Spray on low density, establishing or re-establishing weeds in enclosed water bodies, deeper than 0.5 m and larger than 37.5 cubic metres, or margins of larger still water bodies. See label for restrictions.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Orange oil 55.2 g/kg (Water Clear®)
Rate: 1.0 L per 100 L of water
Comments: Spray on free-floating plants lightly, just enough to change their colour. For non-potable water in artificial and enclosed water bodies.
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.
All of NSW	Prohibition on certain dealings Must not be imported into the state, sold, bartered, exchanged or offered for sale.
Central West	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
Greater Sydney	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment.
Hunter An exclusion zone is established for all land in the region, except the core infestation which includes parts of: Lake Macquarie Local Government Area, MidCoast Local Government Area, Port Stephens Local Government Area.	Regional Recommended Measure* (for Regional Priority - Containment) Entire Hunter Local Land Services region: Land managers should mitigate the risk of the plant being introduced to their land. Exclusion zone: Notify local control authority if found. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Core infestation: Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value. This Regional Recommended Measure applies to Salvinia molesta and Salvinia minima
North West	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found.
Riverina	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. Notify local control authority if found. Your local biosecurity weeds officer can help to identify, advise on control, and how to remove this weed.
South East	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should eradicate the plant from the land and keep the land free of the plant. A person should not deal with the plant, where dealings include but are not limited to buying, selling, growing, moving, carrying or releasing the plant. 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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Reviewed 2023