Sagittaria (Sagittaria platyphylla)

Also known as: arrowhead

Sagittaria is an aquatic weed in New South Wales, capable of aggressive growth and rapid spread.

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How does this weed affect you?

Sagittaria spreads quickly and forms dense infestations in wetlands and natural watercourses where it can:

• reduce or change water flows, increasing the risk of flooding
• outcompete native water plants
• reduce water quality
• restrict movement of fish and other aquatic animals
• reduce food and habitat for fish and other aquatic animals
• make recreation activities such as swimming, boating and fishing difficult
• reduce the visual appeal of waterways.

 In irrigation channels and crops it:

• traps silt which gradually fills the channel bed
• limits water flow
• reduces water storage and efficiency of irrigation channels
• can damage infrastructure
• reduces rice yields
• harbours plant viruses.

What does it look like?

Sagittaria is a perennial water weed up to 1.2 m tall.

It has three growth forms:

1. Submerged (under water) rosette form All plants start off in this form where the entire plant is under water. Plants can stay in this form for years without growing vertical stems. The rosette form does not produce flowers or seeds but can produce rhizomes and corms. Emergent forms develop from submerged rosettes when water is less than 1 m deep.
2. Broad-leaved emergent (above water) form. This form grows in slow-moving water, along river banks and at the edge of infestations. It produces flowers and fruit. If broad-leaved plants are damaged by flooding, herbicide or grazing, they re-emerge as the narrow-leaved form.
3. Narrow-leaved emergent form This form has grass-like leaves. If the plant stays healthy it will start producing broad-leaves again.

Leaves:

The leaves vary in shape and size and may be submerged or above the water.

Emergent (above water) leaves are:

• oval-shaped with a pointed tip
• up to 48 cm long and 10 cm wide
• on stalks up to 55 cm long and triangular in cross-section
• shiny and hairless
• with one main mid-vein.

Submerged (under water) leaves are:

• narrow
• strap-like
• up to 50 cm long.

Flowers are:

• have 3 petals that are white or sometimes pinkish
• are about 3 cm in diameter
• grow in 2-12 whorls of 3 flowers along a leafless stem
• male flowers are above the female flowers
• are present during warmer months.

Fruit are:

• round clusters made up of many one-seeded fruitlets
• 5-15 mm long

Seeds are:

• oblong and flattened with a beak at the tip
• 1.5-3 mm long
• winged
• produced from September to May.

Stems are:

• up to 50 cm long
• triangular cross section

Roots:

Sagittaria has rhizomes and corms. The corms are:

• up to 40 mm long and 15 mm wide
• produced in response to stress such as dry soils, herbicide application and cold weather.

Similar looking plants

Sagittaria looks similar to two other weeds:

• Arrowhead (Sagittaria calycina var. calycina), which has distinctive arrow shaped leaves and round rather than triangular leaf stalks.
• Alisma (Alisma lanceolatum), which has spear-shaped leaves with up to 7 prominent veins running longways along the leaf. It also has smaller flowers (10 mm wide) above the height of the leaves.

 Two Australian native plants also look similar:

• Water plantain (Alisma plantago-aquatica), which has many veins in the leaves and smaller flowers (10 mm wide) that are in clusters held higher than the leaves
• Star fruit (Damasonium minus), which has smaller oval up to 10 cm long and smaller flowers (6 mm wide) which are in clusters above the leaves.

Where is it found?

Sagittaria grows in southern NSW, particularly in the Murray Irrigation District. It is common in the Greater Sydney and Hunter and also grows on the North Coast region. Isolated infestations are also present:

• near Bingara in the North West
• at Dubbo in the Central West
• at Bega in the South East

Sagittaria is native to North America. It was introduced as an ornamental plant. The first plant was identified in Australia in 1959 near Brisbane.

What type of environment does it grow in?

Sagittaria grows in warm temperate and subtropical climates. It grows best in sites with fluctuating water levels and silty sediment, including small channels and on the inside bends of rivers.

The broadleaf emergent form grows in warm, shallow and slow-flowing water. The submerged rosette form can grow in deeper water than the emergent forms. The different forms can grow together and submerged rosettes may grow amongst crowded broadleaf plants.

Frosts may kill or damage the above-water parts of the plants but the plants can regrow from the submerged parts.

Sagittaria grows in:

• irrigation channels and drains
• creeks and rivers
• lagoons and dams
• wetlands.

Maps and records

• Recorded presence of Sagittaria 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 seed

The broadleaf form of the plant can produce hundreds of thousands of seeds. Seed can float for up to 3 weeks before sinking and then remain dormant until conditions are right. Seed usually germinate from late winter to spring when there is an ideal amount of light and the outer seed coat has absorbed enough water. As well as flowing water, seeds are spread by animals including livestock and birds.

By plant parts

Sagittaria can reproduce from stems, root fragments, underground rhizomes and corms. These plant parts can be spread by floods or people dumping aquarium or pond plants. Corms are dormant through winter and produce new growth in spring, though they can remain viable in the soil for many years. Corms allow rapid regeneration of sagittaria following periods of stress. 

References

Aquatic Plant Services (2004), The Biology and Control of Arrowhead, Goulburn-Murray Water.

Chapman, M. & Dore, D. (2006). Arrowhead Strategic Plan Final Draft, Gommalibee, Victoria: Rural Plan Pty Ltd.

Crocker, W. (1907), “Germination of seeds of water plants”, Botanical Gazette, Vol. 44, No. 5, pp. 375-380.

Department of Primary Industries Victoria, (2009), Invasiveness assessment - Giant Arrowhead (Sagittaria montevidensis) in Victoria, August 2010 http://www.land.vic.gov.au

Eastern & Western Riverina Noxious Weeds Advisory Group. (2004). Regional Weed Management Plan: Riverina Sagittaria Management Plan

Flower, G. (2003). The Biology and Control of Arrowhead (Sagittaria graminea). River & Catchment Health: Presenting current research in the Goulburn Broken Catchment.

Goulburn-Murray Water. (2001). Arrowhead Sagittaria graminea factsheet , Aquatic Plant Services.

Gunasekera, L. & Krake, K. (2001). Arrowhead – a serious aquatic weed in northern Victoria. In Victorian Landcare and Catchment Management, 19, 7.

Rataj, K. (1972). “Revision of the genus Sagittaria. Part I. (Old World Species)”, Annotationes Zoologicae et Botanicae, 76, pp. 1-36.

Turner, C.E. (2001). “Reproductive Biology of Sagittaria monetividensis Cham. & Schlecht. spp. Calycina (Engelm.) Bogin (Alismataceae)”, Unpublished doctoral dissertation, University of California, Berkeley.

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 seedlings. Using a combination of control methods is usually more successful.

Prevention

Do not grow sagittaria in ponds and never dump aquatic plants in waterways.

If excavators or other machinery are used on sites with sagittaria they should be inspected and washed down before leaving the site.

Controlling water levels can limit the spread of sagittaria. Irrigation channels that constantly have water levels more than 1 m deep can prevent sagittaria from producing flowers and seeds.

To help prevent the spread of sagittaria when fishing or using waterways for other recreational activities:

• avoid running motors or paddling through water plants
• check your boat/watercraft, trailer and equipment for plant material before you leave a site and before launching at a new site
• remember to check the inside of boats, live wells, bilge and bait containers
• remove all plant material that you find before you leave a site and before launching at a new site.

Physical removal

Physical removal is useful near sensitive crops or for irrigation channels that cannot be closed during herbicide applications. Hygiene and containment measures are important during manual removal so that plant fragments do not float downstream and establish. It is also important when excavating to ensure the root and rhizome fragments in the soil are removed to avoid future regeneration. All machinery should be cleaned thoroughly before leaving the site.

By hand

Digging out sagittaria by hand can be used for small infestations and on sensitive sites where herbicide use is not appropriate. Remove all plant fragments, including rhizomes and corms in the soil and sediment.

By machine

Mechanical control can be effective:

• for new or isolated infestations when eradication is possible
• in restoring water flows as it also removes silt build as well as the weeds
• in irrigation channels where the water is used regularly and should not be contaminated by herbicides.

Excavation can be labour intensive and expensive and care should be used so it does not damage the drain or channel structure.

Disposal

Contact your local council for advice on how to dispose of sagittaria in your area.

Chemical control

Tablet herbicide

A tablet form of herbicide is available for controlling sagittaria. The tablets may be put directly into the water or dissolved in water and then injected into the waterways. The volume of the water body needs to be calculated before using these tablets.  

Additional accreditation is required to use table herbicides in waterways.

Biological control

Trials using the fruit-feeding weevil Listronotus appendiculatus to control sagittaria are underway.

Herbicide options

See Using herbicides for more information.

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PERMIT 89861 Expires 30/11/2027
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: 10 L product/100 L water
Comments: Spot spray. Only for use in Aquatic areas (Irrigation and drainage channels) within the Murrumbidgee Irrigation Limited areas of responsibility. DO NOT exceed a maximum of 40 L product/ha. See permit for other critical comments.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
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. At least 50% of the weed biomass must be below the water surface. 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 20L 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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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 Tablelands	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.
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.
Hunter	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. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
Murray Core infestation zone: Berrigan Shire Council, Edward River Council, Murrumbidgee Council. Exclusion zone: Albury City Council, Federation Council, Greater Hume Council, Murray River Council, Snowy Valleys Council.	Regional Recommended Measure* (for Regional Priority - Containment) Within exclusion zone: 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. Within core infestation area: 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. 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 - 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 Eradication whole of region except for Griffith.	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.
Western	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