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Conyza bonariensis

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Herb up to 60 cm, greyish-green, with flowers arranged in small off-white spherical flower heads.

Scientific name: Conyza bonariensis (L.) Cronq.

Common names: hairy fleabane, Argentine fleabane, fleabane

Family: Asteraceae (Compositae)

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: Erigeron bonariensis L., Erigeron linifolius Willd., Leptilon bonariense (L.) Small, Leptilon linifolium (Willd.) Small

Last update: 09/07/2014

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How to recognise it

Annual herb up to 60 cm, covered in short hairs that confer a greyish-green tone to the plant; simple primary stem with terminal panicles, posteriorly with long branches that overtop the main axis.

Leaves: greyish, pilose on both surfaces; basal leaves oblanceolateentire or with 2-5 coarse lobes on each side; upper leaves smaller, linearoblong, entire and sessile.

Flowers: arranged in capitula whose involucral bracts are densely hairy; ligules that are hard to observe (< 0,5 mm).

Fruits: dirty-white cypselas, each one with a pappus of 4-5 mm; (open) capitula with 8-15 mm diameter.

Flowering: June to August.

 
Similar species

The several Conyza species in Portugal are very similar and hard to distinguish. Additionally, the Conyza species hybridize very rapidly among themselves, originating hybrids with intermediate characteristics, causing further difficulty in the identification.

Conyza bonariensis is distinguished from the other species of Conyza (Conyza canadensis, Canadian fleabane, and Conyza sumatrensis, tall fleabane) for having a smaller plant syze and for having bigger and denser capitula (on the fruit) with dirty-white cypselas. It is also the only species that presents the shorter main axis overtopped by the lateral branches.

conyza-comparacao-legenda2

Inflorescences: comparison of the three most common Conyza species in Portugal.

 

Characteristics that aid invasion

It propagates by seed, producing high amounts of seeds (2000 to 230000 seeds per plant) of reduced persistence (2 to 3 years) and a graduated germination. The seeds are efficiently dispersed by the wind, rapidly enhancing their distribution area.

 

Native distribution area

South America.

 

Distribution in Portugal

Mainland Portugal (all provinces), Azores archipelago (all islands), Madeira archipelago (islands of Madeira and Porto Santo).

Geographic areas where there are records of Conyza bonariensis

Other places where the species is invasive

Europe (Spain, France, Italy, Croatia, Greece, Malta, Albania, Czech Republic), South Africa, Australia, New Zealand, Oriental Africa, North America (Mexico and USA), Central America.

 

Introduction reasons

Probably accidental, very ancient.

 

Preferential invasion environments

A ruderal weed species,very frequent in disturbed areas: urban areas, roadsides and crop fields or common lands. It also appears in natural and semi-natural areas (e.g., dunes) normally associated to disturbance events.

 

Impacts on ecossystems

It forms dense areas that prevent the growth of native vegetation.

 
Economic impacts

High costs in applying control methodologies, mainly in crop areas.

It reduces productivity in crop fields.

 
Other impacts

Due to the high production of pollen, it is considered an allergenic plant.

 

 

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 Conyza bonariensis include:

 

Physical control (preferencial methodology)

Hand pulling: it is applied to plants of all sizes. In more compacted substrates, hand pulling should be made during the rainy to facilitate the removal of the root system.

Agricultural practices of soil mobilization (tilling, harrowing): it is applied to plants of all sizes when dense infestations occur. It should be done before flowering.

 

Chemical control

Foliar application of herbicide. Spray with herbicide (active substance: glyphosate) limiting as much as possible its application to the target species. The herbicide application should be done during the early stages of the plant’s development, before the primary axis is developed.

The continued use of this herbicide has recently originated the appearance of several biotopes of Conzya that are resistant to it. However, as long as properly used, the herbicide application constitutes an effective way to reduce invasion.

 

Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.

Alves P, Aguiar C (2012) Três neófitos novos para a Flora de Portugal. Silva Lusitana 20 (1-2): 136-138.

CABI (2012) Conyza bonariensis. In: Invasive Species Compendium. CAB International, Wallingford, UK. Available: http://www.cabi.org/isc/ [Retrieved 10/11/2012].

Dana ED, Sanz-Elorza M, Vivas S, Sobrino E (2005) Especies vegetales invasoras en Andalucía. Consejería de Medio Ambiente, Junta de Andalucía, Sevilla, 233pp.

Dufour-Dror J-M (2012) Alien invasive plants in Israel. The Middle East Nature Conservation Promotion Association, Ahva, Jerusalem, 213pp.

INRB (2011) Avoadinha-peluda – Conyza bonariensis resistente ao glifosato. Boletim técnico. UIPP-BT/09.

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.

Silva L, Corvelo R, Moura M, Carvalho JA, Land EO (2008) Conyza bonariensis (L.) Cronq. In: Silva L, Land EO, Luengo JLR (eds) Flora e fauna terrestre invasora na Macaronésia. Top 100 nos Açores. Madeira e Canárias. Arena, Ponta Delgada, pp. 291-293.

USDA, NRCS. (2012) The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.  Available: http://plants.usda.gov [Retrieved 10/11/2012].

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