Biosecurity Spotters logo

Box elder (Acer negundo)

Box Elder was introduced as an ornamental and is now an invasive weed, especially along watercourses and in moist forests. It can spread into similar damp areas, where it crowds out native plants and can affect waterways.

Key facts

Type: Weed, tree.

Native to: North America.

Established in: NSW, ACT, VIC, SA, WA.

Other names: Box Elder Maple, Ash-leaved Maple, Black Maple.

Best time to act: Look for mass seedling germination in spring; flowering begins from early September, and fruits persist on the plant until or during winter.

Identification

  • It is a deciduous tree, often multi-stemmed, that can grow to 20 m, though weedy plants are commonly about 8 m tall.
  • Its large leaves are usually 20–30 cm long and divided into 3–7 leaflets, sometimes 9; they may be green or white-variegated and turn yellow before falling in autumn.
  • The bark is smooth and light grey or grey-brown, becoming fissured or flaky with age.
  • Small greenish, yellowish-green or sometimes pinkish flowers appear before or with the leaves; male and female flowers are usually on different plants.
  • Its dry winged fruits are paired at the base in a V-shape and spin like propellers as they fall.
  • Look-alike: Sycamore Maple (Acer pseudoplatanus) has simple leaves with 3–5 lobes, rather than leaves divided into separate leaflets, and can grow to 30 m.
  • Look-alike: Other maples and ashes may have compound leaves; ashes have single-winged fruits, while maples have paired fruits forming a V-shaped, propeller-like body.

Where it grows

In Australia it is found or cultivated in southern areas, including cooler districts, riverbanks, watercourses, wet forests and woodlands, and disturbed sites with moist soil.

Why it matters

  • It invades bushland, especially riparian areas and sheltered moist forests, where it crowds and shades out native plants.
  • It can displace native shrubs and trees and prevent their regeneration by growing quickly, shading other vegetation and producing heavy leaf fall.
  • Dense, long-term infestations may trap sediment, contribute to erosion and deplete oxygen in waterways as autumn leaves fall.
  • In urban areas it can come up en masse in garden beds, and its water-seeking roots can invade pipes.

How it spreads

  • Prolifically produced winged seeds can be carried by wind and moving water.
  • It can spread in dumped garden waste and in seeds contained in chipped prunings used as mulch.
  • Plants can resprout after damage and form root suckers.

Control options

  • Avoid planting Box Elder, especially near riverbanks, moist gullies, wet forests or woodlands.
  • Hand-remove seedlings and small trees, or dig out seedlings and saplings.
  • Cut established trees at ground level and treat the cut stems with registered herbicides.
  • Use approved cut-and-paint or stem-injection methods, following the product label.

Hygiene and washdown

  • Do not dump Box Elder garden waste or use chipped Box Elder prunings as mulch, as both are identified routes for spread.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Declared plant. Depending on the declaration, it can be an offence to move it on public roads or sell it, and landowners may be required to control it on their land.
  • Western Australia: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • Australian Capital Territory: Declared pest, prohibited. It is a declared pest throughout the ACT. Dealing with it, such as selling, moving or keeping it, is prohibited.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Australian Capital Territory: Biosecurity Act 2023 (ACT), administered by ACT Biosecurity
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development

Sources