Arrowhead (Sagittaria calycina var. calycina)

Arrowhead is a fast growing water weed with distinct, arrow-shaped leaves. It chokes waterways and irrigation channels.

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How does this weed affect you?

Arrowhead grows quickly and forms dense infestations in wetlands and natural watercourses where it can:

• reduce water flows
• outcompete native water plants
• 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.

 It is also a weed in irrigation channels where it:

• traps silt which gradually fills the channel bed
• limits water flow
• reduces water capacity and efficiency of irrigation channels
• is expensive to remove.

What does it look like?

Arrowhead is most visible in summer and dies back in winter. It grows in two forms. One form is beneath the water as a submerged rosette. The other form is an emergent plant up to 1 m tall above the waterline. Most seedlings appear in spring.

Leaves 

There are two forms of leaves: above water and below water. 

Leaves above water are:

• up to 25 cm long and 20 cm wide
• strongly arrow-shaped with lobes to 15 cm long and 10 cm wide.
• green and prominently veined
• on stalks 8 - 55 cm long. 

Leaves under the water are:

• narrow, strap like
• 2.5–45 cm long and 0.5–2 cm wide
• green.

Flowers

Flowers grow in whorls of 2-12 at the top of a leafless stem. Female flowers are in groups of 3 and male flowers are in groups above the female flowers. All flowers are:

• white with 3 petals
• 25 mm in diameter
• present from summer to early autumn.

Seeds are:

• flattened and beaked at the tip
• 1.5-3 mm long 
• with wings
• produced in autumn.

Roots

• annual roots are fibrous
• perennial roots are short thick rhizomes.

Stems 

Stems are round in cross-section.

Similar looking plants

Arrowhead looks like

• Sagittaria (Sagittaria platyphylla)
• Alisma (Alisma lanceolatum),
• Water plantain (Alisma plantago-aquatica)
• Star fruit (Damasonium minus).

 You can tell them apart by the stems or leaves.

• Sagittaria has a triangular stem.
• Alisma and Water plantain stems are flat on one side with small wings at the base.
• Sagittaria, water plantain and star fruit have oval-shaped leaves.
• Alisma leaves are spear-shaped. 

Where is it found?

Most arrowhead in NSW grows in the Riverina region. It grows in rice crops and irrigation channels. 

It was first recorded in Australia as a garden escape near Sydney in 1926. During the 1960s arrowhead spread to the Murrumbidgee Irrigation Area.

Arrowhead is native to North and South America. 

What type of environment does it grow in?

Arrowhead is usually found in shallow, warm, slow-moving waters including:

• wetlands, swamps and marshes
• drainage gullies
• irrigation channels (especially along edges and in smaller channels)
• flooded paddocks.

Maps and records

• Recorded presence of Arrowhead 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.
  
  

How does it spread?

By seed

Each plant can produce hundreds of thousands of seeds. Seed can float for up to 3 weeks before sinking. Water, birds and other animals spread the floating seeds. Seeds can either sprout immediately or remain dormant until conditions are right for germination.

By plant parts

New arrowhead plants can grow from stem or root fragments.

More information

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Control

Arrowhead is susceptible to herbicide treatments and a number of herbicides are registered to control arrowhead. However, often herbicides will only suppress infestations and regeneration will occur. Foliar applied herbicides act as a ‘chemical mower’, causing an abscission at the base of the stem resulting in the death of standing leaves and stems. Generally these herbicides are not translocated to the submerged rosettes and the rosette plants growing within treated infestations are stimulated by the reduced competition and can transform into new emergent plants.

Water depth can affect efficacy as foliar applied herbicide must come in contact with a large surface area of the plant. In deeper water there is less exposed plant material to treat with herbicide.

Treatments are best applied when water levels are lowest and plant growth is highest to enable maximum uptake of the herbicide. Risks of herbicide residues in irrigation water are also higher at this time. It is currently thought herbicide treatments on sagittaria at the end of the irrigation season are less effective as plants are beginning to overwinter.

Physical removal

Physical removal od arrowhead involves excavation with machinery or manual digging by hand. Physical removal allows water movement to be restored quickly in waterways blocked by infestations. It is also a technique used in areas where herbicide use is inappropriate, such as near sensitive waterways or irrigation channels under continual use.

Appropriate hygiene and containment measures must be applied during manual removal to ensure plant fragments do not float downstream and establish elsewhere. It is also important when excavating to ensure the root and rhizome fragments in the soil are removed to avoid future regeneration.

Excavation can be labour intensive and costly and is generally avoided in irrigation channels where it interferes with the engineering structure of the drain. However in new and isolated infestations where eradication is possible mechanical and manual removal should be considered. By removing all viable plant material and following up with removal of regrowth, eradication is possible. Physical removal can be particularly effective to control isolated or new infestations.

Herbicide options

See Using herbicides for more information.

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: One part product to 50 parts water
Comments: Spot spray.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: One part product to 9 parts water
Comments: Splatter gun.
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 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* 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. This Regional Recommended Measure applies to all species of Sagittaria
Hunter	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. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
Western	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 fulfill the general biosecurity duty for this weed click here

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Reviewed 2020