Japanese walnut
Botanical Name
Juglans ailantifolia
Family
Juglandaceae (walnut)
Also known as
Juglans sieboldiana, heartnut
Where is it originally from?
Japan
What does it look like?
Wide spreading deciduous hardwood tree (<15 m tall) with fissured bark and shoots with glandular hairs. Brown buds open into alternate divided leaves (<60 cm long) on a stalk (<40 cm long). Leaflets (6-18 x 3-8 cm) in groups of 9-17 are usually hairless above, densely hairy on veins below, with sparsely serrated edges. Single male catkins (<15 cm long) hang from stems, where female catkins are on erect spikes and are usually covered with purple hairs. Groups of 9-22 small flowers with prominent pink stigmas (Oct-Nov) are followed by clusters of 10-22 sticky, downy, rust-coloured fruit (25-40 mm) containing hard, thick-shelled nuts.
Are there any similar species?
Juglans regia (<20+ m tall), has 5-9 entire leaflets, and nuts (35-55 mm long) in clusters of 1-3. North American black walnut (J. nigra) has serrated leaves, few nuts, each irregular and sharply ridged.
Why is it weedy?
Long-lived (50 yrs +), canopy tree, prevents recruitment. Produces many, long-lived seed. Probably allelopathic. Tolerates hot to cold, wet to dry, semi shade.
How does it spread?
Water, occasionally dumped nuts. possibly by pigs or possums. Old homesteads and plantations.
What damage does it do?
Forms tall stands to canopy, not succeeded. Favoured by rats. Blocks waterways.
Which habitats is it likely to invade?
Disturbed forest and shrubland, especially edges of watercourses downstream from plantations.
What can I do to get rid of it?
1. Hand pull small plants (all year round). Mulch.
2. Cut trunk and paint stump (all year round): cut trunk near to the ground, and swab freshly cut stump with metsulfuron-methyl 600g/kg (5g/L).
3. Bore and fill (all year round): make 1 hole every 100 mm around the trunk and fill each hole with 5g metsulfuron-methyl 600g/kg.
4. Overall spray small plants (summer only): metsulfuron-methyl 600g/kg (5g/10L).
CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and directions for the purchase, use and storage of the product, are followed and adhered to.
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