False acacia
Botanical Name
Robinia pseudoacacia
Family
Fabaceae (pea)
Also known as
Robinia pseudacacia, black locust, R. pseudoacacia var. rectissima
Where is it originally from?
South Eastern USA
What does it look like?
Deciduous tree (<25 m tall). Young saplings have smooth, green bark, while older trees have deep, furrowed, shaggy, dark bark with flat-topped ridges. Leaves (20-30 cm) are made up of 7-21 thin, round leaflets that are dark green above and pale underneath, and attached in pairs along the leaf stalk. Smaller branches have 1 cm long spines at the base of each leaf stalk. Large, drooping clusters of pea-like, fragrant, white to yellow flowers (1 cm long, Nov-Jan) are followed by shiny, smooth, narrow, flat seed pods (5-10cm long) containing 4 to 8 seeds.
Are there any similar species?
Sophora (kowhai) species can look similar but don't have spines. Gleditsia (honey locust, water locust) species have often twisted seed pods, have thorns on the trunk and narrow leaflets.
Why is it weedy?
Reproduces vigorously by root suckering and stump sprouting to form groves of trees interconnected by a common root system, and also seeds heavily every 1-2 years, with lesser amounts of seed produced in intervening years. The large, fragrant flowers also compete with native plants for pollinating bees.
How does it spread?
Seeds and also by suckering.
What damage does it do?
Dense thickets shade out other plants in open or disturbed sites. Large, fragrant flowers compete with native plants for pollinating bees.
Which habitats is it likely to invade?
Prefers full sun and well drained soils and invades dry and sandy sites, ex-pasture, disturbed forest, disturbed shrubland, forest edges, plantation forest and roadsides.
What can I do to get rid of it?
1. Physical removal - Hand pull seedlings, or dig out entire plant including roots (all year round): Burn, dispose of to refuse or compost in a composting weed bag.
2. Cut and paste (all year round) - Cut the stem/trunk as close to the ground as possible and cover the entire stump with herbicide as soon as possible after cutting. Apply metsulfuron gel (10g/l strength) to the entire cut stem.
3. Foliar spray (Late Spring to late Autumn) - Apply herbicide using a knapsack to small areas and plants <1m tall, or gun and hose for larger infestations. Use the adjuvant recommended on the label.
Apply metsulfuron herbicide (600g/kg active ingredient at 0.5g/L knapsack or 35g/100L gun and hose) + organosilicone penetrant (3ml/L). Note: Overspray will kill other (desirable) broadleaf plants and has residual activity in the soil which aids in killing below ground parts.
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.
What can I do to stop it coming back?
Monitor the site and treat any regrowth or seedlings. Plant a dense cover of native trees or shrubs to produce shade. If possible, track down and remove the seed source.
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