Japanese walnut (Juglans ailantifolia)

Japanese walnut is a deciduous tree up to 15 m high. Its wide spreading foliage limits the growth of other plants.

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How does this weed affect you?

Japanese walnut is an environmental weed that grows in dense stands. It:

  • releases a chemical that prevents other plants from growing under its canopy
  • competes with native plants
  • blocks waterways.

What does it look like?

Japanese walnut is a deciduous tree that can grow up to 15 m tall. It has spreading branches that produce a wide canopy up to 15 m. It can live for over 50 years.

Leaves:

Leaves are up to 90 cm long and made up of 4–8 pairs of opposite leaflets with a single leaflet at the end. Leaflets are:

  • 6–18 cm long and 3–8 cm wide
  • hairy underneath especially on the veins
  • sparsely serrated along the edges.

Flowers:

Each tree has both male and female flowers.

Male flowers are:

  • yellow-green
  • in clusters about 15 cm long that hang down from the stems.

Female flowers are:

  • clustered in groups of 5–22 flowers on upright spikes which are swollen near the stem
  • green with small petals and obvious pinky-red stigmas
  • covered with purple hairs.

Fruit are:

  • green ripening to rust-coloured
  • round and contain hard, thick-shelled nuts
  • 25–40 mm in diameter
  • covered in a furry husk when young
  • in clusters of up to 22 fruit.

Bark is:

  • cracked
  • grey.

Similar looking plants

Japanese walnut looks very similar to other walnuts:

  • Black walnut (Juglans nigra), which usually have glossy rather than dull leaves and the female flowers are in groups of only 2–5 flowers rather than 5–20.
  • Common walnut (Juglans regia), which is taller (up to 30 m), has less leaflets (1–9) and the leaflets do not have serrated edges.

 It also looks similar to these weed species:

  • Tree of heaven (Ailanthus altissima), which is taller, has larger leaves that smell bad when crushed.
  • Rhus tree (Toxicodendron succedaneum), which is a smaller tree and has smaller leaves that turn bright red in autumn.

Where is it found?

Japanese walnut has been grown as an ornamental tree.

It is a weed around Mt Irvine in the Blue Mountains in the Greater Sydney region. In 2021 plants were found north west of Port Macquarie on the North Coast and these plants are under an eradication program.

It is native to Japan. It has become a weed in New Zealand.

What type of environment does it grow in?

Japanese walnut can grow in a range of soils though it prefers moist well drained soils. It grows best in sunny sites and is frost tolerant. It can grow:

  • along waterways
  • in disturbed forests and shrublands
  • in pastures
  • along roadsides.

Maps and records

  • Recorded presence of Japanese walnut during property inspections (Map: Biosecurity Information System - Weeds, 2017-2021)
    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 seeds

Seeds are spread by water, animals and by people dumping garden waste containing nuts.

References

Native Plant Trust USA (2021) Go Botany: Dichotomous Key, Juglandaceae, Juglans retrieved 12 April 2021 from: https://gobotany.nativeplanttrust.org/dkey/juglans/#c1,c2

nzflora. Weed Factsheet Juglans ailantifolia. Retrieved 12 April 2021 from:  http://www.nzflora.info/factsheet/Weed/Juglans-ailantifolia.html

PFAF Plants for a future. Juglans ailanthifolia - Carrière. Retrieved 12 April 2021 from: https://pfaf.org/user/Plant.aspx?LatinName=Juglans+ailanthifolia

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 12 April 2021 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Juglans~ailantifolia 

Rietveld, W. J. (1983). Allelopathic effects of juglone on germination and growth of several herbaceous and woody species. Journal of Chemical Ecology9(2), 295-308.

Weedbusters New Zealand (2017). Weed Information Sheet Japanese Walnut Juglans ailantifolia. Retrieved 12 April 2021 from: https://www.weedbusters.org.nz/what-are-weeds/weed-list/japanese-walnut/pdf/?nocache=1

More information

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Control

If you suspect you have found Japanese walnut contact you local council weeds officer.

Hand weeding

Small plants can be hand pulled year-round.

Chemical control

Basal barking

Apply herbicide mixed with diesel to cover the lower stem, all the way around.

Cut stump method

Cut the stem and then thoroughly cover the cut stem with herbicide within 15 seconds.

Stem injection

Drill or make cuts into the sapwood and fill with herbicide within 15 seconds.

Herbicide options

WARNING - ALWAYS READ THE LABEL
Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website www.apvma.gov.au

See Using herbicides for more information.


PERMIT 9907 Expires 31/03/2025
Fluroxypyr 200 g/L (Comet® 200 herbicide)
Rate: 35 mL per L diesel/kerosene
Comments: Basal bark
Withholding period: Do not graze failed crops and treated pastures or cut for stock feed for 7 days after application. See label for further information.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


PERMIT 9907 Expires 31/03/2025
Fluroxypyr 333 g/L (Staraneā„¢ Advanced)
Rate: 21 mL per L diesel/kerosene
Comments: Basal bark
Withholding period: Do not graze failed crops and treated pastures or cut for stock food for 7 days after application. See label for more information.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
Rate: One part product to 1.5 parts water
Comments: Cut stump, drill, frill axe or injection
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L with Metsulfuron-methyl 600 g/kg (Various products)
Rate: 1:1.5 glyphosate to water + 1 g metsulfuron to 1 L water
Comments: Stem injection
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.
North Coast 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.
*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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For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW DPI Biosecurity Helpline on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2021