Arrowhead (Sagittaria calycina var. calycina)

Arrowhead is an aggressive aquatic weed. It can spread rapidly to block irrigation channels, impede water flows and choke natural watercourses and wetlands.

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How does this weed affect you?

Arrowhead is an aquatic weed capable of aggressive growth and rapid spread. It can block irrigation channels, impede water flows and choke natural watercourses and wetlands.

In natural systems the vigorous, choking habits of arrowhead threaten native aquatic flora and fauna. Dense infestations restrict water flow and can substantially alter the flow regime of catchments and waterways affecting biodiversity and stream health. In irrigation systems it is capable of reducing flow and effectiveness of water delivery. The plant biomass fills the channel bed reducing the volume available for water storage and trapping silt, gradually reducing the capacity of the channel. Infestations also have detrimental impacts on recreational activities such as fishing, boating and swimming, and reduce visual amenity of waterways.

Where is it found?

Arrowhead is native to North and South America and was first recorded in Australia as a garden escape near Sydney in 1926. During the 1960’s arrowhead spread to the Murrumbidgee Irrigation Area near Griffith, and now commonly occurs in rice crops and irrigation channels in the Murrumbidgee Valley. Its distribution is mostly contained to the inland waterways of the Riverina region.

How does it spread?

Arrowhead can reproduce via several methods. It is a prolific seeder, with each plant having the ability to produce hundreds of thousands of seeds. It can also reproduce vegetatively by stem or root fragments, allowing it to spread rapidly, survive adverse conditions and resume growth when conditions are more favourable.

Seed production occurs from September to May. Seed can either germinate immediately or remain dormant only germinating when conditions are favourable. Seed may be dispersed via animals such as stock and birds or by water currents.

Seed can float for up 3 weeks before sinking. This ability aids in dispersal. The stimulus for germination includes sufficient light and water absorption by the outer seed coat.

Arrowhead seeds germinate in spring and plants mature during summer producing flowers from January to March. Seeds mature throughout autumn and adult plants die back during the colder months.

What does it look like?

Arrowhead is an emergent aquatic plant that belongs to the Alismataceae family. Other similar-looking species in this family include sagittaria (Sagittaria platyphylla), alisma (Alisma lanceolatum), water plantain (Alisma plantago-aquatica) and star fruit (Damasonium minus). Table 1 summarises the differences between sagittaria, arrowhead and these similar-looking species. In Victoria, it is common for arrowhead to refer to Sagittaria platyphylla. In NSW, arrowhead refers only to S. montevidensis.

Arrowhead acts as a fibrous-rooted annual reaching 100 cm in height. It generally has two growth forms, submerged rosette and emergent. Arrowhead does not produce rhizomes like sagittaria making it easier to manage.

Leaves and stems

Arrowhead has broad, strongly arrow-shaped emergent leaves up to 25 cm long and 20 cm wide. It has narrow submerged leaves that can occasionally be slightly arrow-shaped. Arrowhead stems are round in cross-section.

Flowers

Arrowhead flowers occur in whorls of 2-12 at the apex of a leafless stem. Female flowers are carried in groups of 3 around the stems, and male flowers occur in groups above the female flowers. There are 3 white petals, 2.5 cm in diameter.

Fruit/seeds

Arrowhead seeds are laterally flattened, 0.15-0.3 cm long with wings.

	SAGITTARIA S. platyphylla	ARROWHEAD S. calycina variety calycina	ALISMA Alisma lanceolatum	WATER PLANTAIN Alisma plantago-aquatica	STAR FRUIT Damasonium minus
Origin	North America	America	Europe, west Asia, north Africa	Native to Australia	Native to Australia
Height	150 cm	100 cm	100 cm	150 cm	100 cm
Distinguishing features	Larger flowers (3 cm wide), oval-shaped leaves with only one main mid-vein	Large flowers (2.5 cm wide), strongly arrow-shaped adult leaves	Narrow leaves and large inflorescence held above the height of the leaves, small flowers (10 mm wide)	Small flowers (10 mm wide), oval-shaped leaves with many veins	Small flowers (6 mm wide), large inflorescence held above leaves
Leaves	Emergent leaves: oval-shaped with a pointed tip; to 25 cm long and 10 cm wide. Submerged leaves: long, narrow strap-like without expanded blades; to 50 cm long	Emergent leaves: arrow-shaped; prominently veined; to 25 cm long and 20 cm wide; lobes to 15 cm long and 10 cm wide. Submerged leaves: strap-like, linear	Spear-shaped; to 20 cm long and 4 cm wide; up to 7 prominent veins connected by several transverse veins. Submerged leaves: strap-like	Oval-shaped; 10-25 cm long and 7-10 cm wide; usually 7 prominent parallel veins connected by numerous transverse veins	Oval-shaped; 5-10 cm long and 1.5-4 cm wide; 3-5 parallel veins connected by numerous finer transverse veins
Stems (leaf stalk)	Triangular in cross-section; to 80 cm long.	Round in cross-section	To 80 cm long; flattened on one side with small wings at the base	To 80 cm long, flattened on one side with small wings at the base	To 30 cm long
Flowers	Appear in whorls or coils. Male flowers: 3 white petals with yellow centre; 3 cm wide. Female: no petals; look like flattened green berries. Flowers appear below the height of the leaves during spring to autumn	Female flowers carried in groups of 3 ringing the stem, with male flowers in groups above them; all borne on a leafless stem. Petals are white. Flowers are 2.5 cm wide	Inflorescence (flower cluster) to 60 cm long and 40 cm wide. Flowers 10 mm diameter. Sepals to 2 mm long. Petals 4 mm long, white or pink. Flowers in summer	Wiry inflorescence (flower cluster), to 60 cm long and 40 cm wide. Flowers 10 mm diameter. Sepals to 2 mm long. Petals 4 mm long, pale pink or almost white. Flowers on long stems above height of leaves	Inflorescence (flower cluster) to 50 cm long. Flowers 6 mm in diameter. Sepals 1 mm long, green. Petals ovate 6 mm long, white or pink. Flowers early summer
Fruit/Seed	Cluster 0.5-1.0 cm across; 1 seeded segment flattened and winged 1.5-3 mm long. Each plant can produce up to 20,000 seeds	Clustered; laterally flattened, 1.5-3 mm long, beaked at the apex with dorsal wings	Triangular; 2-2.5 mm long. Each fruit contains 1 seed	2-2.5 mm long, falling singly	Star-shapedÈ

What type of environment does it grow in?

Arrowhead is usually found in shallow flooded areas such as marshes and wetlands and is commonly found in crops such as rice. Drainage gullies, rice fields, permanent swamps and areas associated with irrigation drainage are favoured habitat.

Arrowhead will establish easily along the edges of irrigation channels (berms). The water depth and flow rates allow seed to settle and plants to establish. The smaller channels provide ideal conditions for infestation, as the water is generally warmer, shallower and slower moving. Fluctuations in depth allow plants to establish while the water is shallow.

Acknowledgements

Authors: Lauren Forrest, Melissa Kahler and Elissa van Oosterhout.
Technical reviewers: John Fowler, Birgitte Verbeek, Stephen Johnson

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. Available at 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.

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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 31/03/2020
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 31/03/2020
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 2018