The situation of Baccharis halimifolia in the EPPO region
Baccharis halimifolia (Asteraceae – common name Salt Bush) is listed on the EPPO List of invasive alien plants. It originates from North America, and is invasive in the EPPO region. It has been introduced as an ornamental plant for its tolerance to salinity and wind.
EPPO region: Belgium, France, Italy, Spain, United Kingdom.
North America: Mexico (native), USA (native) (Alabama, Arkansas, Connecticut, District of Columbia, Florida, Georgia, Louisiana, Massachusetts, Maryland, Mississippi, North Carolina, New Jersey, New York, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Texas, Virginia).
Oceania: Australia (invasive) (New South Wales, Queensland), New Zealand (invasive).
B. halimifolia is a branching shrub or small tree growing up to 4 m high. The trunk can reach 16 cm diameter. Leaves are alternate, pale green, thick, those of the stem and lower branches obovate to elliptic or oblanceolate, 2-7 cm long and 1-5 cm wide, those of the branchlets are smaller, cuneate at the base, several-toothed above the middle. B. halimifolia is dioecious. Flower heads are situated in terminal or axillary clusters of 1 to 5. Flowers are small, female ones are whitish, male ones are greenish. Achenes are 1-2 mm long, pappus is bright-white, 6-8 mm long.
Biology and ecology
B. halimifolia is generally an evergreen, but in the cooler parts of its native range, it is deciduous. The species reproduces mainly by seeds, but can also reproduce vegetatively by sprouting. B. halimifolia flowers at the end of the summer (August to October in France) and is wind-pollinated. Seeds are produced from October to November (in France). They are abundant (about 1 million seeds are produced by one female plant) and germinate easily (usually in 1 to 2 weeks) if sufficient soil moisture is available. Seed longevity is of about 5 years. Optimum germination conditions are at temperatures comprised between 15 and 20°C. B. halimifolia grows fast and shrubs are mature within 2 years and flower every year.
B. halimifolia tolerates a high level of soil salinity as well as periodic floods, it can stand many types of soil and pH. It is frost tolerant, and can stand temperatures as low as -15°C.
In its native range, this shrub is found mostly in coastal habitats, e.g. salt marshes and tidal rivers, sandy places, but also on disturbed places far off the coast. In its introduced range, the species first colonizes anthropized habitats such as road sides, ditches, wastelands, etc. and then reaches semi-natural to natural habitats such as wetlands. According to the Corine Land Cover nomenclature, these habitats correspond to: coastal wetlands, banks of continental water, riverbanks/canalsides (dry river beds), road and rail networks and associated land, other artificial surfaces (wastelands).
The species has been introduced in France at the end of the 18th century, and is much appreciated for ornamental purposes due to its tolerance to salt and wind. Seeds are dispersed by wind and possibly by water.
B. halimifolia forms dense and impenetrable thickets that crowd out native vegetation and prevent the establishment of other plant species, including rare and vulnerable plant species.
When established near salt marshes, B. halimifolia is detrimental to salt production as ti forms a wind break and contamines salt with seeds. B. halimifolia also impedes treatments against mosquitoes in wetlands. The plant is very inflammable and may increase fire hazards, as well as the cost of wasteland management. The palatability of the plant is low, which can reduce the value of pastures. Seeds are poisonous if eaten and lethal cases of poisoning of cattle have been reported. Its pollen is also suspected to be allergenic and to cause hay fever.
The first step in controlling this species is the reduction of its use as an ornamental plant along roads.
Flooding with marine water could limit the spread of the species. Nevertheless, such a technique can only be considered in salt marshes. ;
Cutting and uprooting can locally control the plant, but these expensive measures have to be repeated several times because of the resprouting ability of the species, and the large seed bank. If plants are removed manually, the roots should be cut well below the soil surface to prevent resprouting. When uprooting is not possible, regularly cutting the shrubs before they set seeds can stop the spread of the plant. Sheep grazing can reduce the spread of B. halimifolia locally, when there is a heavy pasture load (the species has a low palatability).
Chemical control is done by spraying herbicides such as 2,4-D, dicamba plus MCPA, glyphosate, picloram plus 2,4-D, and tryclopyr.
Control through fire has proven to be inefficient. Several biological control agents have been tested, but are not regarded as highly efficient.
Charpentier A, Riou K, Thibault M (2006) Bilan de la campagne de contrôle de l’expansion du Baccharis halimifolia menée dans le parc naturel régional de Camargue (PNRC) en automne 2004 et 2005. http://www.parc-camargue.fr/Francais/upload/rapport_baccharis.pdf
Delivering Alien Invasive Species Inventories for Europe (DAISIE). http://www.europe-aliens.org/
Muller S (2004) Baccharis halimifolia In: (2004) Plantes invasives en France. (Ed. Muller S) pp. 40-43. 2004 Muséum national d’Histoire naturelle, Paris (FR), (Patrimoines naturels, 62).
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