Hygrophila (Hygrophila costata)

Hygrophila is an upright plant that grows over a metre tall in shallow water. It forms dense mats along the edges of creeks and water bodies and outcompetes native plants.

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How does this weed affect you?

Hygrophila is a water weed that:

• forms dense mats that outcompete other plants
• reduces stream flows
• reduces food and habitat for fish and other aquatic animals
• limits access to water bodies
• restricts boating and fishing.

What does it look like?

Hygrophila can grow in shallow water rooted in the mud, extend out over the water from the banks and grow as floating mats. It usually grows to 1.5 m high but can reach up to 2.5 m high when it scrambles over other vegetation. It grows quickly in warm weather.

Leaves are:

• green
• up to 18 cm long and 5 cm wide
• tapered at the base
• prominently veined with a distinct midrib
• hairy
• in opposite pairs along the stems.

Flowers are:

• white or mauve
• up to 9 mm long
• a tube with five lobes
• sparsely hairy
• in whorls growing just above where leaves join the stem
• present in summer.

Fruit are:

• capsules with up to 20 seeds
• 7-13 mm long
• egg-shaped with tapered ends
• difficult to see
• present from summer to early autumn.

Seeds are:

• pale brown
• 0.3-1.0 mm wide
• round
• flattened
• sticky when wet.

Stems are:

• sometimes red to purplish
• squarish and grow vertically
• branched lower down but rarely on the upper part of stems.

Similar looking plants

Hygrophila looks like:

• East Indian hygrophila (Hygrophila polysperma), which has smaller leaves (up to 8 cm long), and flowers that are bluish-white.
• Alligator weed (Alternanthera philoxeroides), which has white flowers on stalks and completely hollow stems.
• Senegal tea (Gymnocoronis spilanthoides), which has irregularly toothed leaf margins, ribbed stems that are hollow between the joints, pom-pom-like white or pale purple flower heads in clusters.
• Smartweed (Persicaria decipiens), which has alternate, hairy leaves.
• Water primrose (Ludwigia peploides ssp. montevidensis), which has yellow flowers and alternate glossy leaves.

Where is it found?

Hygrophila usually grows in subtropical coastal regions. It is invasive in the far north coast, central coast and Greater Sydney regions of NSW.

Hygrophila is native to Central and South America and has naturalised in many tropical and subtropical areas around the world.

What type of environment does it grow in?

In NSW, hygrophila grows in shallow freshwater, along creek banks and in shallow wetlands. It is often found at disturbed sites where native vegetation has been removed and the water has very high nutrient levels.

Maps and records

• Recorded presence of Hygrophila 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?

Plants have been spread by people dumping aquarium or pond plants in waterways.

By seed

Water, animals, wind and watercraft can spread the seed.

By plant parts

Plants can grow from cuttings or severed leaves. Leaves can sprout roots if they are left floating on the water’s surface. Stem fragments sprout new roots when they come in contact with the soil.

Water, animals, machinery and watercraft can spread plant parts.

References

Csurhes, S. (2008). Glush weed. Hygrophila costata. Plant pest risk assessment. Queensland Department of Primary Industries and Fisheries.

Grantly, J., McPherson, F., & Petroeschevsky, A. (2009). Recognising Water Weeds: Plant Identification Guide. NSW Industry & Investment

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 8 September 2020 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Hygrophila~costata

Sainty, G. R., & Jacobs, S. W. (2003). Waterplants in Australia (No. Ed. 4). Sainty and Associates Pty Ltd.

More information

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Control

Successful weed control relies on follow up after the initial efforts. This means regularly looking for any new plants or plant fragments and controlling them.. Using a combination of control methods is usually more successful.

Contact your local council weeds officer for help identifying hygrophila, and advice on controlling it.

By hand

Collect and dispose of all plant fragments when physically removing hygrophila. Ask your local council for advice on how to dispose of this weed.

Herbicide options

See Using herbicides for more information.

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PERMIT 14729 Expires 30/06/2024
Metsulfuron-methyl 600 g/kg (Various products)
Rate: 5–10 g per 100 L of water
Comments: Minimise off target damage and water pollution by spraying towards the bank. Do not apply more than 3 times a year.
Withholding period: Nil (recommended not to graze for 7 days before treatment and for 7 days after treatment to allow adequate chemical uptake in target weeds).
Herbicide group: B, Inhibitors of acetolactate synthase (ALS inhibitors)
Resistance risk: High

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: 100 mL in 10 L of Water
Comments: Spot spray application.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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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.
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 - 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.
Hunter	Regional Recommended Measure* (for Regional Priority - Eradication) 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.
North Coast Exclusion (eradication) zone: Bellingen Shire LGA, Clarence Valley LGA, Coffs Harbour City LGA, Kempsey Shire LGA, Lord Howe Island, Port Macquarie-Hastings LGA, Nambucca Valley LGA. Core infestation (containment) zone: Ballina Shire LGA, Byron Shire LGA, Kyogle Shire LGA, Lismore City LGA, Richmond Valley LGA, Tweed Shire LGA.	Regional Recommended Measure* (for Regional Priority - Containment) Whole of region: Land managers should mitigate the risk of the plant being introduced to their land. A person should not buy, sell, move, carry or release the plant into the environment. 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. Core infestation: Land managers should mitigate spread of the plant from their land. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
North 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.
	*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