Evergreen tree, of dark green leaves in the shape of a scythe and golden yellow spherical flower heads.
Scientific name: Acacia pycnantha Bentham
Common name: golden wattle
Family: Fabaceae (Leguminosae)
Status in Portugal: invasive species (listed in the annex I of Decreto-Lei n° 565/99, of 21 December)
Risk Assessment score: (in development)
Synonymy: Acacia falcinella Meissner, Acacia petiolaris Lehm, Acacia westoni Maiden
Last update: 30/06/2014
How to recognise it
Shrub or tree up to 8m, with a smooth, grey rhytidome.
Leaves: evergreen, reduced to phyllodes with 6-20 x 0,5-5 cm (up to 10 cm width in the sprouts that form on the stumps of cut trees), asymmetric on the base, falcate, muticous, with a longitudinal vein.
Flowering: January to April.
Acacia saligna (Port Jackson wattle) is relatively similar, but their phyllodes are symmetric on the base, generally mucronate, and greenish-blue in colour. It also presents fewer clusters per raceme (just 2-10). Crudely, the falcate leaves resemble an eucalypt but is well distinguished by the presence of a characteristic aroma and by the flowering.
Characteristics that aid invasion
It reproduces by seed, producing many seeds that remain viable in the ground for many years.
The species also propagates vegetatively, forming shoots from the stump in some situations.
Native distribution area
Southeast Australia (Victoria).
Distribution in Portugal
Mainland Portugal (Beira Litoral, Beira Baixa, Estremadura, Ribatejo, Alto Alentejo, Algarve).
Other places where the species is invasive
Europe (Spain), South Africa, some regions of Australia.
For ornamental purposes and tannin extraction.
Preferential invasion environments
Dry disturbed places, for example on roadsides.
In the native environment it grows in dry sclerophyllous forests, mainly in sandy or rocky soils.
Impacts on ecossystems
It forms very dense populations inhibiting the development of native vegetation. In Portugal, it is not one of the most dispersed species, being known few (when compared with A. dealbata, A. melanoxylon or A. longifolia) situations where these levels of impact are verified.
It produces a lot of nitrogen-rich litter, which promotes soil change.
It has potential expensive control measures.
Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.
The control methodologies used for Acacia pycnantha include:
Hand pulling: preferential methodology for seedlings and small plants. When in more compacted substrates, hand pulling must be made during the rainy season as to facilitate the removal of the root system. It should be guaranteed that no stumps and main roots are left in the ground.
Cutting: preferential methodology for adult plants. Cut the tree as close to the ground as possible by using manual and/or mechanical equipment. It should be done before seed maturation. Most times, this operation is enough for the effective control of the species. However, there are situations where the sprouting occurs after cutting, making necessary the application of this methodology in posterior interventions in combination with other methodologies, namely the application of herbicide.
Physical + chemical control
Cut stump method: Apply to adult plants. Cut the trunk as close to the ground as possible and immediately (in the following seconds) apply herbicide (active substance: glyphosate) to the cut stump. If shoots should latter on appear, these should be immediately eliminated through cutting, pulling or foliar application of herbicide (active substance: glyphosate); up to 25 to 50 cm high. Shoots of larger dimensions (from 2-3 cm diameter) may be ring-barked or else should be repeated the initial methodology (cut stump method).
Foliar application of herbicide: over recent sprouts (25-50 cm tall) or when high germination rates occur. Spray with herbicide (active substance: glyphosate) limiting as much as possible its application to the target species.
The wasp Trichilogaster signiventris B (Hymenoptera: Pteromalidae), which forms galls on the buds of A. pycnantha, it was introduced in South Africa in 1987, currently verifying extensive damage in the target species.
The weevil Melaterius maculatus (Coleoptera: Curculionidae) is also successfully used in South Africa to control this species.
These agents have not yet been tested in Portugal as to verify its safety relatively to native species, so its use has not yet constituted an alternative in our country.
It may be strategically used to favour germination of the seed bank, e.g., after the control of adult individuals (with the adequate management of the resulting biomass) and the subsequent elimination of seedlings. This method provides an advantageous reduction of the seed bank, both by destroying part of the seeds or by stimulating the germination of the remainders.
Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.
Agricultural Research Council – Plant Protection Research Institute – Weed Research Division (2014) Management of invasive alien plants: A list of biocontrol agents released against invasive alien plants in South Africa. Available: http://www.arc.agric.za/arc-ppri/Documents/WebAgentsreleased.pdf [Retrieved 03/03/2014].
Dennill GB, Donnelly D, Stewart K, Impson FAC (1999) Insect agents used for the biological control of Australian Acacia species and Paraserianthes lophanta (Willd.) Nielsen (Fabaceae) in South Africa. African Entomology: Memoir no.1: 45-54.
Marchante E, Freitas H, Marchante H (2008) Guia prático para a identificação de plantas invasoras de Portugal Continental. Imprensa da Universidade de Coimbra, Coimbra, 183pp.
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