What does it look like?
Tree lupin is a short lived perennial shrub that grows up to 2–3 metres tall. It has a deep taproot and tough, branching stems that are densely silky hairy when young, becoming soft and woody as the plant matures.
The leaves are grey green and made up of 5–11 narrow leaflets that spread out like fingers from a single point. The upper surface of the leaves is smooth, while the underside is silky to the touch.
From October to May, the plant produces pale yellow, sweet scented, pea like flowers, occasionally tinged blue or white. These are followed by stout, softly hairy seed pods that stay firmly attached to the plant. When mature, the pods split open suddenly, scattering mottled dark brown seeds.
Why is it a problem?
Tree lupin grows and matures quickly, producing many long-lived seeds. It’s taller than competing coastal species, so can form a canopy. It tolerates wind, salt, hot to cold temperatures, damage and grazing (not readily eaten), drought, low fertility (fixes nitrogen), and fire but is intolerant of moderate shade and waterlogged soils, short tussockland, bare land, riverbeds, coastal, sandy and well-drained areas.
Seeds are spread by explosive pods, water and soil movement. Sown for sand consolidation and erosion control and as a nursery crop. Common seed sources are riverbeds and plantation forests. It lowers light levels in open habitats, causing later invasion by weedy shrubs, vines, wilding pines, etc. Increased soil nitrogen may induce changes in the species making up the plant communities from low fertility species to exotic grass or other weed species. It causes sand and gravel to build up, altering the shape of coastlines or rivers and causing erosion elsewhere. Increased cover prevents some birds (eg dotterels, wrybills) nesting and increases predation of birds that do by cats and mustelids.
Control methods
Control probably only necessary in low-growing plant communities, eg coastal dunes.
- Slash tall plants close to ground (all year round). Leave on site to rot down.
- Hand pull or dig small plants (all year round). Leave on site to rot down.
- Cut down and paint stumps (all year round): glyphosate (200ml/L) or metsulfuron-methyl 600g/kg (1g/L) or triclopyr 600 EC (100ml/L) or triclopyr 120g/L (500ml/L) or picloram gel.
- Spray (active growing period): clopyralid (50ml/10L) or triclopyr 600 EC (15ml/10L) or triclopyr 120g/L (75ml/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.
Cut stumps occasionally resprout as it has a persistent seedbank. Recent fungal attack has lowered this plants vigour. Sites with strong tall regeneration can usually be left for falling light levels to eliminate. This process can be assisted by slashing and/or interplanting.
More information
Similar to Blue lupin (Lupinus angustifolius) - a semi-woody annual with blue flowers (Aug-Apr). L. polyphyllus is also similar. Hybrid L. arboreus x polyphyllus has larger and more leaflets, flowers are yellow with blue or purple streaks but is rarely weedy.
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