General description

Wide-spreading, deciduous tree < 15 m tall. Leaves are < 60 cm long with long petioles. Male catkins are c. 15 cm long. Flowers are red/pink/purple and borne in October – November. Fruit is obovoid and < 4 cm long.

What you need to know

To help protect our environment:

You must not breed, distribute, release or sell Japanese walnut. As Japanese walnut is a National Pest Plant Accord species, these restrictions apply within the Auckland region and across the whole of New Zealand.
You must not plant Japanese walnut within the Auckland region, unless you are transferring an existing plant on your land to another location within the boundaries of the same property.
You must destroy any Japanese walnut on land that you occupy if it has been planted in breach of the above rules and you are directed to do so by an authorised person.

Habitats

Riparian margins, wetlands, roadsides, scrub, disturbed forest, grasslands, drainage channels.

Dispersal

Seeds dispersed by water and possibly rodents. Human-mediated dispersal through deliberate plantings.

Impact on environment

Forms dense stands, excluding native vegetation. Allelopathic.

Control

Site Management

Follow up treated areas 3 times per year. Encourage natural regeneration of native plants or replant treated areas where possible after 2-3 treatments to establish dense ground cover and minimise reinvasion.

Recommended approaches

Physical control

Method: Dig out

Plant parts requiring disposal: Seeds

Disposal options: Remove to greenwaste or landfill

Biocontrol

Biocontrol is currently not available for this species.

Community agrichemical control recommendations

No qualifications
Cut stump and paste freshly cut base of stems with metsulfuron gel

Basic Growsafe certified
Cut stump and spray freshly cut base with 5g metsulfuron-methyl per 1 L of water

Certified Handler/Experienced agrichemical user
Drill and inject trees with 5g metsulfuron-methyl per 1L of water if safe to do so. Drill 18mm holes (tangentially angled downwards) in a spiral up the trunk. For 50mm stems drill one hole. For 100mm stems drill two holes. For larger stems drill holes 150mm apart.
Foliar spray seedlings with 5g metsulfuron-methyl per 10L of water and 20ml penetrant

Safety notes

Large trees must not be drilled that are closer than 1.5 times the height of the tree from paths, walkways and property.

Trees over 4 metres in height should be treated and then removed by a qualified arborist.

CAUTION: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.