Black willow (Salix nigra)

Black willow is an invasive tree of rivers, streams and wetlands. It is considered one of the most serious weeds of riparian and wetland ecosystems in Australia. It is a Weed of National Significance.

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How does this weed affect you?

Black willow is an invasive woody weed of rivers, streams and wetlands throughout temperate Australia. It is considered one of the most serious weeds of riparian and wetland ecosystems in Australia, where it spreads quickly and forms dense stands along water courses.

Black willows were originally planted during the 1960s for soil stabilisation projects along streams and river banks in Victoria and southern NSW. They are now considered to cause erosion and flooding, and reduce water availability and quality.

Where is it found?

Black willow is native to eastern Canada, and eastern and central USA, particularly along the Mississippi River. In its native range it can form large stands and has commercial importance. Black willow does not appear to be a problematic weed in any other part of the world.

In NSW, the largest infestations of black willow occur in the Hawkesbury-Nepean and Murrumbidgee catchments, which are subject to ongoing control and monitoring programs. Black willow has the potential to invade rivers, streams and wetland areas throughout NSW.

Distribution map

• NSW (image)

How does it spread?

Black willow spreads mostly from seed but can also grow from broken stems. A female tree produces thousands of light fluffy seeds each year that can travel by wind or water. Seeds will only survive for a couple of weeks, yet under ideal conditions (bare wet ground in full sunlight) germination is fast and a mass of seedlings may be seen in about a month.

Stem fragments may break off and travel many kilometers downstream. New roots will grow in water from these fragments, resulting in new infestations.

Black willow is able to hybridise (cross-pollinate) and breed with other willow species.  This may increase problems caused by other Salix species.

What does it look like?

Black willow is an upright deciduous tree that stands up to 20 m high, usually with one trunk but able to have up to 4 main stems. Young trees have a conical shape which broadens with age. Male and female trees are equally common.

Key identification features

• Bark is rough, dark brown-to-grey in colour, with deep fissures (splits or cracks in the bark) on older stems. Twigs are a shiny red-brown in the sun and brittle at the base, snapping easily from the main stem.
• Leaves are bright green, slender, 4–10 cm long and 7–17 mm wide with toothed edges.
• Flowers are long slender catkins, a stalk of many petal-less flowers, which are either male or female (on separate trees). Male catkins are 6–12 cm long with widely spaced fragrant yellow flowers. Female catkins are 4–6 cm long with green bulbous ovaries on short stalks. Catkins appear in spring with new leaves.
• Capsules are 4.5–5.5 mm long and tiny seeds are covered in long silky hairs.

What type of environment does it grow in?

Black willows prefer open sunny positions and will grow along the banks of streams, rivers, lagoons and swamps, spreading their roots out into the water. Once established they can spread further into a water course, taking up large amounts of water, and eventually diverting the natural flow.

Acknowledgements

Reviewed by: Michael Michelmore; Edited by: Elissa van Oosterhout

References

Holland Clift, S and Davies, J (2007). Willows National Management Guide: current management and control options for willows (Salix spp.) in Australia. Victorian Department of Primary Industries, Geelong.

Jacobs, SWL and Murray, L (2000). Salix nigra spp., in PlantNET - The Plant Information Network System of The Royal Botanic Gardens and Domain Trust, Sydney, Australia. Available at http://plantnet.rbgsyd.nsw.gov.au

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Control

A local council weeds officer will assist with identification, control information, removal and eradication. Very few herbicides are registered for use near water and extreme care must be taken to avoid contact with any non-target species.

Herbicide options

See Using herbicides for more information.

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Glyphosate 360 g/L (Roundup®)
Rate: 1.0–1.3 L in 100 L of water
Comments: Spray to wet all foliage. Use the higher rate for trees 1–2 m high.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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Glyphosate 360 g/L (Roundup®)
Rate: Undiluted
Comments: Stem injection.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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Picloram 44.7 g/kg + Aminopyralid 4.47 g/L (Vigilant II ®)
Rate: Undiluted
Comments: Cut stump/stem injection application. Apply a 3–5 mm layer of gel for stems less than 20 mm. Apply 5 mm layer on stems above 20 mm .
Withholding period: Nil.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate

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Triclopyr 240 g/L + Picloram 120 g/L (Access™ )
Rate: 1.0 L per 15 L of diesel
Comments: Cut stump application method, for plants in excess of 5cm basal diameter
Withholding period: Nil
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
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.
All of NSW	Prohibition on dealings Must not be imported into the State or sold
Greater Sydney	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.
Greater Sydney	Regional Recommended Measure* 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.
Murray	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 Coast Exclusion zone: all lands in the region, except the core infestation area of: Clarence Valley Council and Nambucca Valley Shire Council	Regional Recommended Measure* Exclusion zone: The plant should be eradicated from the land and the land kept free of the plant. Land managers should mitigate the risk of the plant being introduced to their land. Core infestation area: Land managers reduce impacts from the plant on priority assets.
North West	Regional Recommended Measure* Land managers should mitigate the risk of new weeds being introduced to their land. Land managers should mitigate spread from their land.
Riverina	Regional Recommended Measure* Land managers should mitigate the risk of the plant being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant.
	*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