Baccharis halimifolia | Tree Groundsel
Regulated invasive species of Union concern under the European Regulation on the prevention and management of the introduction and spread of invasive alien species [1143/2014].
Introduction pathways - 1
Release in Nature
Introduction pathways subclass - 1
Release in nature for use, Ornamental purpose
NAPRA Ireland risk assessed
A dioecious woody shrub or small tree, up to 4m (EPPO, 2014). Leaves are obovate or elliptic and entire or with 2-6 teeth on the upper part of the leaf (Nesom, 2001). Flowers are inconspicuous, female whitish, male greenish and are borne in clusters on stalks. Fruit are achenes with a silvery tuft (pappus). The pappus catches in the wind and enables dispersal over a wide area. Mature plants have deeply fissured bark (CABI, 2017). Normally evergreen but can be deciduous in cooler parts of its range (CABI, 2017).
Fast growing, up to 40cm per annum (Rozas Ormazabal et al, 2012) shrubs that form dense monospecific thickets that monopolise resources and outcompete native plants. They are long lived, up to 25 years (EPPO, 2014) and so can completely transform the landscape. Tolerant of recurrent flooding and drying (CABI, 2017) as well as a wide range of soil nutrient levels and salinity (Nesom, 2001). Resistant to frost (Rozas Ormazabal et al, 2012). The dense stands provide protection for mosquito larvae from insecticide application (Brunel et al., 2010). Inflammable resin is produced by the leaves and wood increasing the frequency of fires (Brunel et al., 2010). However, it is not controlled by fire and will readily resprout from the base (Nesom, 2001). Pollen is produced in vast quantities and can cause hay fever type allergies (Herrera & Campos in EPPO, 2016). The leaves contain a cardiotoxic glycoside, which causes staggering, diarrhoea, trembling and convulsions and which can be fatal to grazing animals if consumed in great enough quantities (Nesom, 2001).
Principally littoral zones
Reproduces mainly by seed dispersal. The pappus are readily carried on the wind and can be dispersed over 5-6km (CABI, 2017). Seeds are produced in abundance and have a high germination percentage (Nesom, 2001). They may also be dispersed by water (CABI, 2017) and feasibly by animals. Also capable of sprouting from rootstock.
Pathway and vector description
Imported for use as an ornamental plant, particularly in coastal gardens due to its tolerance of salinity in soil and spray (CABI, 2017; Miller, 2002; Nesom, 2001) and its effectiveness as a windbreak (CABI, 2017). From there it readily disperses its seed. It was also used by municipal authorities to stabilise shorelines in tidal areas and as an ornamental plant along roadsides (EPPO, 2014).
Mechanism of impact
There is currently an EU wide ban on the sale, growing and keeping of this plant (European Commission, 2017).
For small plants hand removal is the most effective method (Department for the Environment and Territorial Policy of the Basque Government, 2014). Care must be taken that the whole root is removed. It is particularly effective if it can be done before the plants reach reproductive age (EPPO, 2016) thus eliminating the risk of spread by seed dispersal. Larger plants must be dug out or cut off more than 10cm below the soil surface (EPPO, 2016). Since the seed bank is estimated to last up to 2 years it is essential that cutting be carried out before the plants set seed (EPPO, 2016).
Digging using heavy machinery can be effective especially if carried out in the dormant season but can only be used in areas considered not to be of conservation value (Department for the Environment and Territorial Policy of the Basque Government, 2014).
Glyphosate gives good control. It is most effective if sprayed during flowering, August to October (EPPO, 2016). It can also be applied to the tree stump within 30 seconds of cutting (Department for the Environment and Territorial Policy of the Basque Government, 2014) and can give 97% success in small to medium sized infestations (EPPO, 2016). Manual methods should then be used in the following seasons to remove the new plants produced from the seed bank. In wet areas holes 5cm apart can be drilled in the stems and the herbcide instilled with a dropper or syringe. The holes should then be sealed up with resin (Department for the Environment and Territorial Policy of the Basque Government, 2014).
Pruning to 50cm above ground level and covering with polyethylene plastic or geotextile secured with rope (Department for the Environment and Territorial Policy of the Basque Government, 2014) is a slow method but it may be useful in sensitive areas.
Areas that have been treated should be regularly monitored for the presence of regrowth or recolonisation (Rozas Ormazabal, 2012).
Should be disposed of by incineration or by stacking with roots uppermost to prevent contact with the soil or water (EPPO, 2016).
Margins of coastal wetlands and estuaries but also sand dunes, fallow fields, hedgerows, waste-ground, woodlands, reedbeds and irrigation ditches.
Introduced to Australia, New Zealand, Asia (Georgia) and Europe (Belgium, France, Italy, Spain, the UK). The risk analysis carried out by the European and Mediterranean Plant Protection Organisation (2013) lists Ireland as one of the countries most at risk of invasion.
Native to North America (South Eastern states), Mexico, and the Caribbean. It is also native to Canada where it is regarded as an extremely rare species (EPPO, 2014).
Records submitted to Data Centre in 2022
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How can you help
Do not compost this species. Do not purchase or plant in your garden. Dispose of unwanted plants responsibly. Report sightings to the National Biodiversity Data Centre http://www.biodiversityireland.ie/projects/invasive-species/submit-sightings/
Brunel, S; Schrader, G; Brunder, G; Fried, G. (2010). Emerging invasive alien plants for the Mediterranean Basin. Bulletin OOEP/EPPO. Bulletin 40 (2), pp. 219-238. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2338.2010.02378.x/pdf Site accessed 16 August 2017.
CABI (2017). Invasive Species Compendium – Datasheet report for Baccharis hamilifolia (Grounsel-bush). Wallingford, UK: CAB International. http://www.cabi.org/isc/datasheet/8164 Site accessed 4 September 2017.
Department for the Environment and Territorial Policy of the Basque Government (2014) Baccharis halimifolia Management manual. Ihobe, Department for the Environment and Territorial Policy, Basque Government. 109 p. http://www.ingurumena.ejgv.euskadi.eus/contenidos/documentacion/baccharis/en_def/adjuntos/BaccharisHalimifoliaManagementManual_%20EN.pdf Site accessed 5 September 2017.
EPPO. (2016). PM9/23 (1) Baccharis halimifolia. EPPO Bulletin, 46 (3), pp. 567–575. doi:10.1111/epp.12338 http://onlinelibrary.wiley.com/doi/10.1111/epp.12338/full Site accessed 4 September 2017.
EPPO. (2014). Data sheets on invasive alien plants Baccharis halimifolia L. Asteraceae – Groundsel Bush . EPPO Bulletin, 44 (1), pp. 5–10. DOI: 10.1111/epp.12089 http://www.eppo.int/INVASIVE_PLANTS/ias_lists.htm Site accessed 4 September 2017.
EPPO. (2013). Report of a pest risk analysis for Baccharis halimifolia. EPPO. Paris. https://gd.eppo.int/taxon/BACHA/documents Site accessed 4 September 2017.
European Commission. (2017). Invasive Alien Species of Union Concern. European Union, Luxembourg.
Miller, C. (2002). Plant Fact Sheet. Eastern baccharis baccharis halimifolia L. United States Department of Agriculture - Natural Resources Conservation Services (USDA-NRCS) https://plants.usda.gov/factsheet/pdf/fs_baha.pdf Site accessed 4 September 2017.
Nesom, G (2001). Groundsel Tree—Baccharis halimifolia L.. USDA Natural Resources Conservation Service Plant Guide. https://plants.usda.gov/plantguide/pdf/pg_baha.pdf Site accessed 4 September 2017.
Rozas Ormazabal M et al. (2012). Restoration of habitats of Community interest in the Basque Country's estuaries. Layman Report Life+ estuaries of the Basque country project (LIFE08NAT/E/0055). http://www.ingurumena.ejgv.euskadi.eus/contenidos/documentacion/baccharis/en_def/adjuntos/BaccharisHalimifoliaManagementManual_%20EN.pdf Site accessed 5 September 2017.
CABI Datasheet (http://www.cabi.org/isc/datasheet/8164)
Was recorded in the Netherlands but seems to be no longer present (van Valkenburg in EPPO, 2014).