Scientific name: Robinia pseudoacacia L.
Common names: black locust, false acacia, locust tree, yellow locust
Family: Fabaceae (Leguminosae)
Risk Assessment score: 32 | 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.
Last update: 01/07/2021
How to recognise it
Leaves: deciduous, odd-pinnate, with 3-11 pairs of elliptic or ovate leaflets, with 15-60 x 4,5-30 mm, glabrous, with an apex generally retuse (less times, acute) and mucronate; robust spiny stipules.
Flowers: white, flashy, arranged in pendulous racemes.
Flowering: April to June.
Gleditsia triacanthos L. honey locust) also has robust spines, but they are divided in three parts, have smaller leaflets and much larger pods (up to 40 cm). Sophora japonica L. (pagoda tree) has similar leaves, but doesn’t have spiny stipules, the leaflets have an acute apex and the pod is strongly constricted between the seeds. Amorpha fruticosa L. (indigobush) has similar leaves but is a shrub, has purple flowers and much smaller pods.
Characteristics that aid invasion
Though it produces many seeds, most of them do not germinate.
Native distribution area
Central and Eastern North America.
Distribution in Portugal
Mainland Portugal (Minho, Trás-os-Montes, Douro Litoral, Beira Alta, Beira Baixa, Beira Litoral, Estremadura, Ribatejo, Alto Alentejo, Algarve).
Geographic areas where there are records of Robinia pseudoacacia
Europe (Spain, France, Greece, Hungary, Germany, Holland, United Kingdom, Cypress), Asia (Israel, turkey), South Africa, North America (Canada, Mexico, USA), South America (Argentina), Australia, New Zealand.
For ornamental, medicinal and forest reasons, as well as to stabilize soils.
Preferential invasion environments
Roadsides and banks of watercourses, disturbed areas. It appears in the understory of arboreal vegetation, even though it prefers a sunny location.
It develops in all types of soils but it prefers the light, fresh, sandy and dry soils.
Impacts on ecossystems
It may form monospecific dense populations (sometimes they form a large clone connected by the root system) inhibiting the development of species that need sun.
It produces a lot of nitrogen-rich litter, which promotes soil change.
Expensive control methodologies.
Natura 2000 network habitats more subject to impacts
– Alluvial forests with Alnus glutinosa (Alno-Padion, Alnion incanae, Salicion albae) (91E0);
– Riparian mixed forests of Quercus robur, Ulmus minor and Fraxinus angustifolia, along the great rivers (91F0);
– Salix alba and Populus alba galleries (92A0);
– Galicio-Portuguese oak woods with Quercus robur and Quercus pyrenaica (9230);
– Quercus faginea and Quercus canariensis Iberian woods (9240).
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 Robinia pseudoacacia include:
Hand pulling: preferential methodologyfor 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 main roots are left in the ground.
Physical + chemical control
Cut stump method: applied 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 ring-barked off or else should be repeated the initial methodology (cut stump method).
Stem injection : preferential methodology for plants with a diameter larger than 5 cm. Apply the herbicide directly on the vascular system by making several cuts (with an axe or saw), at the height most convenient to the operator, in an angle of 45º until the sapwood, and immediately inject (in the following seconds) the herbicide (active substance: glyphosate or triclopyr) in each incision with a squirt bottle. Apply around 1ml (0,5 to 2ml, according to the size of the cut) of herbicide in each incision.
The several cuts should be made at the same height on the trunk as to nearly touch, leaving around 2-4 cm of uncut bark between them. For smaller individuals, only 2 or 3 cuts are necessary and they shouldn’t be deep (to prevent the plant breaking).
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.
Basal bark method: applied to seedlings up to 15 cm diameter. The herbicide application (active substance: glyphosate or triclopyr) should be made at a height of 30 cm. For larger plants, the herbicide application should be preceded by ring-barking.
Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.
Dufour-Dror J-M (2012) Alien invasive plants in Israel. The Middle East Nature Conservation Promotion Association, Ahva, Jerusalem, 213pp.
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.
Wieseler S (2005) Black locust – Robinia pseudoacacia L. In: Plant Conservation Alliance’s Alien Plant Working Group. Weeds gone Wild: Alien Plant Invader of Natural Areas. Available: http://www.nps.gov/plants/alien/fact/rops1.htm [Retrieved 06/11/2012].