Also known as
Butterfly bush, summer lilac
Where is it originally from?
What does it look like?
Deciduous (occasionally semi-evergreen) open, multi-stemmed shrub (<3+ m tall). Stems are bluntly angled, clad in tufts of easily-removed soft woolly hair (downy hairs when young), and become lax when long. Thin, willow-shaped leaves (6-20 x 3-8 cm) are usually hairless above, white or hairy grey underneath, and finely toothed. Distinctive, dense, cone-shaped hanging clusters (30 x 5 cm) made up of many fragrant purple or white flowers (5 mm diameter, Dec-Feb) with orange insides are followed by seed capsules (5-10 mm long).
Are there any similar species?
Several pink and mauve hybrids and cultivars are also sold.
Why is it weedy?
Establishes and grows quickly, and forms self-replacing thickets. Extremely ecologically versatile, tolerating a wide range of (especially poor) soils, hot to cold (likes frost), wet to moderately dry conditions, deep shade or open areas, damage, and wind.
How does it spread?
Seed is spread by wind and water, soil movement, and dumped vegetation. Plantation forest, wasteland, roadsides, gardens and parks are all sources of infestation.
What damage does it do?
Forms dense stands in wide range of habitats. In riverbeds it can alter water flow, causing silt buildup and flooding.
Which habitats is it likely to invade?
River beds, streamsides, disturbed forest and shrubland and margins, short tussockland, pumice, lava, and stony and bare land. Major pest, often only exotic species found in forests in mountain regions.
What can I do to get rid of it?
1. Pull or dig small plants. Leave on site to rot down.
2. Cut stump application: Apply glyphosate (250ml/L) or a product containing 100g picloram+300g triclopyr/L (250ml/L) to horizontally cut stumps.
3. Bore and fill: Drill holes sloping into the sapwood at regular intervals around the tree. Place a mixture of glyphosate (250ml/L) or a product containing 100g picloram+300g triclopyr/L (undiluted) into each hole.
4. Frilling: With a sharp chisel or axe, make a deep cut into the sapwood at regular intervals around the base of the tree ensuring the plant is not ring-barked. Immediately apply a mixture of glyphosate (250ml/L) or a product containing 100g picloram+300g triclopyr/L (undiluted) to the cuts using a paintbrush or squeeze bottle.
5. Spray (Feb-Apr): glyphosate (10ml/L) or metsulfuron-methyl 600g/kg (5g/10L) or a product containing 100g picloram+300g triclopyr/L (90ml/15L (knapsack) or 250ml/100L (spraygun)).
What can I do to stop it coming back?
Seed bank reinfests bared sites. Cut stumps resprout. Difficult to prevent reinvasion. Follow up 6-monthly. Maintain rolling front.