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Acacia pycnantha

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 Decreto-Lei nº 92/2019, 10 july)

Risk Assessment score: 23 | Value obtained according to a protocol adapted from the Australian Weed Risk Assessment (Pheloung et al. 1999), by Morais et al. (2017), according to which values above 13 mean that the species has risk of having invasive behavior in the Portuguese territory | Updated on 30/09/2017.

Synonymy: Acacia falcinella Meissner, Acacia petiolaris Lehm, Acacia westoni Maiden

Last update: 30/06/2021

Family: 
Fabaceae (Leguminosae)
Appearence: 
Trees and shrubs

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.

Flowers: golden yellow arranged in globular flower heads, of 8-10 mm diameter, in turn arranged (10-20) in racemes or panicles.

Fruits: dark brown or nearly black pods, compressed, sub-straight; seeds with short, whitish funicle.

Flowering: January to April.

 

Similar species

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).

 

 

Geographic areas where there are records of Acacia pycnantha

Other places where the species is invasive

Europe (Spain), South Africa, some regions of Australia.

 

Introduction reasons

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.

 

Economic impacts

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:

 

Physical control

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).

 

Chemical control

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.

 

Biological control

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.

 

Prescribed fire

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">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.