Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Conyza canadensis
(Canadian fleabane)

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Datasheet

Conyza canadensis (Canadian fleabane)

Summary

  • Last modified
  • 19 November 2019
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Natural Enemy
  • Host Plant
  • Preferred Scientific Name
  • Conyza canadensis
  • Preferred Common Name
  • Canadian fleabane
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • C. canadensis is now a common weed in temperate to tropical regions. It is a mainly annual herbaceous weed spreading by producing high numbers of wind-dispersed seeds. It prefers undisturbed sites and is a particular problem in low-tillage systems su...

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Pictures

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PictureTitleCaptionCopyright
Conyza canadensis (Canadian fleabane); Habit, often seen standing 2m tall or taller along the American River trail system. Rancho Cordova, California, USA. August 2019.
TitleHabit
CaptionConyza canadensis (Canadian fleabane); Habit, often seen standing 2m tall or taller along the American River trail system. Rancho Cordova, California, USA. August 2019.
Copyright©Matt Lavin/via Flickr - CC BY-SA 2.0
Conyza canadensis (Canadian fleabane); Habit, often seen standing 2m tall or taller along the American River trail system. Rancho Cordova, California, USA. August 2019.
HabitConyza canadensis (Canadian fleabane); Habit, often seen standing 2m tall or taller along the American River trail system. Rancho Cordova, California, USA. August 2019.©Matt Lavin/via Flickr - CC BY-SA 2.0
Conyza canadensis (Canadian fleabane); Seeds with pappus. August 2014.
TitleSeeds with pappus
CaptionConyza canadensis (Canadian fleabane); Seeds with pappus. August 2014.
Copyright©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Seeds with pappus. August 2014.
Seeds with pappusConyza canadensis (Canadian fleabane); Seeds with pappus. August 2014.©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Flowers. Hockenheim, Baden-Württemberg, Deutschland. October 2017.
TitleFlowers
CaptionConyza canadensis (Canadian fleabane); Flowers. Hockenheim, Baden-Württemberg, Deutschland. October 2017.
Copyright©Andreas Rockstein/via Flickr - CC BY-SA 2.0
Conyza canadensis (Canadian fleabane); Flowers. Hockenheim, Baden-Württemberg, Deutschland. October 2017.
FlowersConyza canadensis (Canadian fleabane); Flowers. Hockenheim, Baden-Württemberg, Deutschland. October 2017.©Andreas Rockstein/via Flickr - CC BY-SA 2.0
Conyza canadensis (Canadian fleabane); Flowers. July 2010.
TitleFlowers
CaptionConyza canadensis (Canadian fleabane); Flowers. July 2010.
Copyright©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Flowers. July 2010.
FlowersConyza canadensis (Canadian fleabane); Flowers. July 2010.©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Flowers. September 2009.
TitleFlowers
CaptionConyza canadensis (Canadian fleabane); Flowers. September 2009.
Copyright©Dalgial/via Wkimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Flowers. September 2009.
FlowersConyza canadensis (Canadian fleabane); Flowers. September 2009.©Dalgial/via Wkimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Seeding habit. July 2006.
TitleSeeding habit
CaptionConyza canadensis (Canadian fleabane); Seeding habit. July 2006.
Copyright©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Seeding habit. July 2006.
Seeding habitConyza canadensis (Canadian fleabane); Seeding habit. July 2006.©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Seedhead. August 2010.
TitleSeedhead
CaptionConyza canadensis (Canadian fleabane); Seedhead. August 2010.
Copyright©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Seedhead. August 2010.
SeedheadConyza canadensis (Canadian fleabane); Seedhead. August 2010.©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Seeding habit. Hockenheim, Baden-Württemberg, Deutschland. October 2017.
TitleSeeding habit
CaptionConyza canadensis (Canadian fleabane); Seeding habit. Hockenheim, Baden-Württemberg, Deutschland. October 2017.
Copyright©Andreas Rockstein/via Flickr - CC BY-SA 2.0
Conyza canadensis (Canadian fleabane); Seeding habit. Hockenheim, Baden-Württemberg, Deutschland. October 2017.
Seeding habitConyza canadensis (Canadian fleabane); Seeding habit. Hockenheim, Baden-Württemberg, Deutschland. October 2017.©Andreas Rockstein/via Flickr - CC BY-SA 2.0
Conyza canadensis (Canadian fleabane); Foliage and seedheads. Ash Creek Spring, Calico Basin, Nevada, USA. September 2008.
TitleFoliage and seedheads
CaptionConyza canadensis (Canadian fleabane); Foliage and seedheads. Ash Creek Spring, Calico Basin, Nevada, USA. September 2008.
Copyright©Stan Shebs/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Foliage and seedheads. Ash Creek Spring, Calico Basin, Nevada, USA. September 2008.
Foliage and seedheadsConyza canadensis (Canadian fleabane); Foliage and seedheads. Ash Creek Spring, Calico Basin, Nevada, USA. September 2008.©Stan Shebs/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Seeding habit. Villiago, Belluno, Italy. October 2008.
TitleSeeding habit
CaptionConyza canadensis (Canadian fleabane); Seeding habit. Villiago, Belluno, Italy. October 2008.
Copyright©Enrico Blasutto/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Seeding habit. Villiago, Belluno, Italy. October 2008.
Seeding habitConyza canadensis (Canadian fleabane); Seeding habit. Villiago, Belluno, Italy. October 2008.©Enrico Blasutto/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Foliage. Hamilton Parish, Bermuda. July 2009.
TitleFoliage
CaptionConyza canadensis (Canadian fleabane); Foliage. Hamilton Parish, Bermuda. July 2009.
Copyright©Sam Fraser-Smith/via Flickr - CC BY 2.0
Conyza canadensis (Canadian fleabane); Foliage. Hamilton Parish, Bermuda. July 2009.
FoliageConyza canadensis (Canadian fleabane); Foliage. Hamilton Parish, Bermuda. July 2009.©Sam Fraser-Smith/via Flickr - CC BY 2.0
Conyza canadensis (Canadian fleabane); Vegetative stage. September 2012.
TitleHabit
CaptionConyza canadensis (Canadian fleabane); Vegetative stage. September 2012.
Copyright©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
Conyza canadensis (Canadian fleabane); Vegetative stage. September 2012.
HabitConyza canadensis (Canadian fleabane); Vegetative stage. September 2012.©Rasbak/via Wikimedia Commons - CC BY-SA 3.0
C. canadensis vegetative stage.
TitleVegetative stage
CaptionC. canadensis vegetative stage.
Copyright©Chris Parker/Bristol, UK
C. canadensis vegetative stage.
Vegetative stageC. canadensis vegetative stage.©Chris Parker/Bristol, UK
Leaves of C. canadensis (left), C. sumatrensis (middle) and C. bonariensis (right).
TitleLeaf comparison
CaptionLeaves of C. canadensis (left), C. sumatrensis (middle) and C. bonariensis (right).
Copyright©Chris Parker/Bristol, UK
Leaves of C. canadensis (left), C. sumatrensis (middle) and C. bonariensis (right).
Leaf comparisonLeaves of C. canadensis (left), C. sumatrensis (middle) and C. bonariensis (right).©Chris Parker/Bristol, UK

Identity

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Preferred Scientific Name

  • Conyza canadensis (L.) Cronq. (1943)

Preferred Common Name

  • Canadian fleabane

Other Scientific Names

  • Erigeron canadensis L.
  • Erigeron pusillus Nutt.
  • Trimorpha canadensis (L.) Lindm.

International Common Names

  • English: horseweed
  • Spanish: erigeron del Canada; escoba dura; hierba de caballo; hierba impia; olivarda
  • French: erigéron du Canada; vergerette du Canada
  • Portuguese: avoadinha

Local Common Names

  • Canada: mare's tail
  • Colombia: cvenadillo
  • Cuba: conyza; zancarana
  • France: erigeron de Canada; vergerette de Canada
  • Germany: Kanadischer berufkraut; Kanadisher katzenschweif
  • India: jarayupriya
  • Iraq: thail el-faras
  • Italy: impi; saeppola
  • Japan: himemukashiyomogi
  • Madagascar: sarijamala
  • Mauritius: herbe gandi
  • Mexico: pegajosa
  • Netherlands: fijnstraal, Canadeese
  • Norway: canadese fijnstraal; hestehamp
  • Poland: przymiotno kasnadyjskie
  • Puerto Rico: pascueta; rozuz
  • South Africa: armoedskruid; kanadese skraalhans
  • Spain: altabaca; canem bord; erigeron de Canada; zamarraga
  • Sweden: kanadabinka
  • Turkey: sifa out
  • USA: butterweed; Canada horseweed; fireweed; hogweed
  • Yugoslavia (Serbia and Montenegro): repusnjaca

EPPO code

  • ERICA (Erigeron canadensis)
  • ERIPS (Erigeron pusillus)

Summary of Invasiveness

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C. canadensis is now a common weed in temperate to tropical regions. It is a mainly annual herbaceous weed spreading by producing high numbers of wind-dispersed seeds. It prefers undisturbed sites and is a particular problem in low-tillage systems such as orchards, plantations but also in some agricultural crops. It may be controlled by tillage at a suitable growth stage, but otherwise, it has developed resistance to many herbicides in a large number of countries. It has been introduced internationally as a contaminant of cereals, forage seeds and cotton, and there is a risk of further similar introduction to countries where it is not yet established. It could become a problem invasive in protected areas, though may be controlled naturally as it is an early-successional species, often being replaced by perennial grasses.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Asterales
  •                         Family: Asteraceae
  •                             Genus: Conyza
  •                                 Species: Conyza canadensis

Notes on Taxonomy and Nomenclature

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The species was first described by Linnaeus as Erigeron canadensis in 1753, and transferred to the genus Conyza in 1943 by Cronquist. C. canadensis is a clearly defined species and is not nomenclaturally confused with any other related species, unlike several others within the genus (see datasheets on C. bonariensis and C. sumatrensis). It is, however, still widely referred to by its older name, Erigeron canadensis. Thebauld and Abbott (1995) noted that C. canadensis was the only diploid species of five invasive European species tested, and was more closely related to the genus Erigeron than the other taxa. This supports a hypothesis that C. canadensis is older in evolutionary terms.

Description

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C. canadensis is an erect annual with a long taproot and one or more stems arising from a basal rosette, it is usually about 1 m high but may be much taller. Leaves are up to 10 cm long and about 1 cm wide with some shallow teeth, clear green (not greyish as in other common Conyza species), almost glabrous on the surfaces, but with some scattered hairs. Leaf margins ciliate and with longer conspicuous hairs towards the leaf base. Flower heads are very numerous on short pedicels, only 2-3 mm in diameter when fresh (broader in pressed specimens), involucral bracts about 5 mm long, glabrous. Disc florets yellow, contrasting with distinct white ray florets which are 0.5 to 1 mm long, the latter distinguishing C. canadensis from other common weedy Conyza species. Seeds 1.0-1.3 mm long with 10-25 off-white pappus hairs, 2-4 mm long (Holm et al., 1997).

Plant Type

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Annual
Biennial
Broadleaved
Herbaceous
Seed propagated

Distribution

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C. canadensis is native to North America (USA and Canada) but spread to Europe as early as the 1600s (Michael, 1977) and later to much of Asia and Australia, including tropical regions such as in the Americas. However, in Africa it is so far restricted to north and south subtropical regions (Holm et al., 1997). In Bhutan, it is restricted to higher elevations, over 2000 m (Parker, 1992) but is apparently not so restricted in Central America. The native range elsewhere in the Americas remains obscure, but it is considered as exotic in Central America and the Caribbean in this datasheet. Weaver (2001) reported that the species was native to all provinces of Canada except Newfoundland, whereas USDA-ARS (2004) included Newfoundland in the native range.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Last updated: 01 Jun 2021
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes

Africa

EswatiniPresentIntroduced
LesothoPresentIntroduced
MadagascarPresentIntroduced
MauritiusPresentIntroduced
MozambiquePresentIntroduced
NigeriaPresentIntroduced
South AfricaPresentIntroduced
SudanPresentIntroduced
TunisiaPresentIntroduced
ZimbabwePresentIntroduced

Asia

BhutanPresentIntroduced
ChinaPresentIntroduced
-AnhuiPresent
-HebeiPresentIntroducedOriginal citation: Wang et al., 1990
-HenanPresentIntroducedOriginal citation: Wang et al., 1990
-JiangxiPresentIntroducedOriginal citation: Wang et al., 1990
-ShaanxiPresentIntroducedOriginal citation: Wang et al., 1990
-ShandongPresentIntroducedOriginal citation: Wang et al., 1990
-ShanxiPresentIntroducedOriginal citation: Wang et al., 1990
-SichuanPresentIntroducedOriginal citation: Wang et al., 1990
-YunnanPresentIntroduced
-ZhejiangPresentIntroducedOriginal citation: Wang et al., 1990
IndiaPresent, WidespreadIntroduced
-HaryanaPresentIntroduced
-Jammu and KashmirPresentIntroducedOriginal citation: Siddiq et al. (1987)
-UttarakhandPresent
IndonesiaPresentIntroduced
IranPresentIntroduced
IraqPresentIntroduced
IsraelPresentIntroduced
JapanPresentIntroduced
-HokkaidoPresent, WidespreadIntroduced
-HonshuPresent, WidespreadIntroduced
-KyushuPresent, WidespreadIntroduced
-Ryukyu IslandsPresent, WidespreadIntroduced
-ShikokuPresent, WidespreadIntroduced
JordanPresentIntroduced
North KoreaPresent, WidespreadIntroduced
PakistanPresentIntroduced
PhilippinesPresent, WidespreadIntroduced
South KoreaPresent, WidespreadIntroduced
TaiwanPresent, WidespreadIntroduced
ThailandPresentIntroduced
TurkeyPresentIntroduced
VietnamPresentIntroduced

Europe

AlbaniaPresentIntroducedInvasive
AndorraPresentIntroducedInvasive
AustriaPresentIntroducedInvasive
BelarusPresentIntroducedInvasive
BelgiumPresentIntroducedInvasive
Bosnia and HerzegovinaPresentIntroducedInvasive
BulgariaPresentIntroducedInvasive
CroatiaPresentIntroducedInvasive
CzechoslovakiaPresentIntroducedInvasive
Federal Republic of YugoslaviaPresentIntroducedInvasive
DenmarkPresentIntroducedInvasive
EstoniaPresentIntroducedInvasive
FinlandPresentIntroducedInvasive
FrancePresentIntroducedInvasive
GermanyPresentIntroducedInvasive
GibraltarPresentIntroducedInvasive
GreecePresentIntroducedInvasive
HungaryPresentIntroducedInvasive
ItalyPresentIntroducedInvasive
LatviaPresentIntroducedInvasive
LiechtensteinPresentIntroducedInvasive
LithuaniaPresentIntroducedInvasive
LuxembourgPresentIntroducedInvasive
MoldovaPresentIntroducedInvasive
MonacoPresentIntroducedInvasive
NetherlandsPresentIntroducedInvasive
North MacedoniaPresentIntroducedInvasive
NorwayPresentIntroducedInvasive
PolandPresentIntroducedInvasive
PortugalPresentIntroducedInvasive
-AzoresPresent
RomaniaPresentIntroducedInvasive
RussiaPresentPresent based on regional distribution.
-Central RussiaPresentIntroducedInvasive
-Southern RussiaPresentIntroducedInvasive
San MarinoPresentIntroducedInvasive
SerbiaPresent
Serbia and MontenegroPresentIntroducedInvasive
SlovakiaPresentIntroducedInvasive
SloveniaPresentIntroducedInvasive
SpainPresentIntroducedInvasive
-Canary IslandsPresentIntroducedInvasive
SwedenPresentIntroducedInvasive
SwitzerlandPresentIntroducedInvasive
UkrainePresentIntroducedInvasive
United KingdomPresentIntroducedInvasive

North America

BelizePresentIntroduced
CanadaPresent, WidespreadNative
-AlbertaPresentNative
-British ColumbiaPresentNative
-ManitobaPresentNative
-Newfoundland and LabradorPresentNative
-Northwest TerritoriesPresentNative
-Nova ScotiaPresentNative
-NunavutPresentNative
-OntarioPresentNative
-Prince Edward IslandPresentNative
-QuebecPresentNative
-SaskatchewanPresentNative
-YukonPresentNative
Costa RicaPresentIntroduced
CubaPresentIntroducedInvasive
El SalvadorPresentIntroduced
GuatemalaPresentIntroduced
HondurasPresentIntroduced
JamaicaPresentIntroduced
MexicoPresentIntroduced
NicaraguaPresentIntroduced
PanamaPresentIntroduced
Puerto RicoPresentIntroduced
Trinidad and TobagoPresentIntroduced
Turks and Caicos IslandsPresentIntroduced
United StatesPresentPresent based on regional distribution.
-AlabamaPresent, WidespreadNative
-ArizonaPresent, WidespreadNative
-ArkansasPresent, WidespreadNative
-CaliforniaPresent, WidespreadNative
-ColoradoPresent, WidespreadNative
-ConnecticutPresent, WidespreadNative
-DelawarePresent, WidespreadNative
-FloridaPresent, WidespreadNative
-GeorgiaPresent, WidespreadNative
-HawaiiPresent, WidespreadIntroduced
-IdahoPresent, WidespreadNative
-IllinoisPresent, WidespreadNative
-IndianaPresent, WidespreadNative
-IowaPresent, WidespreadNative
-KansasPresent, WidespreadNative
-KentuckyPresent, WidespreadNative
-LouisianaPresent, WidespreadNative
-MainePresent, WidespreadNative
-MarylandPresent, WidespreadNative
-MassachusettsPresent, WidespreadNative
-MichiganPresent, WidespreadNative
-MinnesotaPresent, WidespreadNative
-MississippiPresent, WidespreadNative
-MissouriPresent, WidespreadNative
-MontanaPresent, WidespreadNative
-NebraskaPresent, WidespreadNative
-NevadaPresent, WidespreadNative
-New HampshirePresent, WidespreadNative
-New JerseyPresent, WidespreadNative
-New MexicoPresent, WidespreadNative
-New YorkPresent, WidespreadNative
-North CarolinaPresent, WidespreadNative
-North DakotaPresent, WidespreadNative
-OhioPresent, WidespreadNative
-OklahomaPresent, WidespreadNative
-OregonPresent, WidespreadNative
-PennsylvaniaPresent, WidespreadNative
-Rhode IslandPresent, WidespreadNative
-South CarolinaPresent, WidespreadNative
-South DakotaPresent, WidespreadNative
-TennesseePresent, WidespreadNative
-TexasPresent, WidespreadNative
-UtahPresent, WidespreadNative
-VermontPresent, WidespreadNative
-VirginiaPresent, WidespreadNative
-WashingtonPresent, WidespreadNative
-West VirginiaPresent, WidespreadNative
-WisconsinPresent, WidespreadNative
-WyomingPresent, WidespreadNative

Oceania

AustraliaPresentIntroduced
-QueenslandPresentIntroduced
-South AustraliaPresentIntroduced
-TasmaniaPresentIntroduced
-Western AustraliaPresentIntroduced
FijiPresent, WidespreadIntroduced
New ZealandPresentIntroduced
Papua New GuineaPresent, WidespreadIntroduced

South America

BrazilPresentIntroduced
ChilePresentIntroduced
ColombiaPresentIntroduced
EcuadorPresentIntroduced
GuyanaPresentIntroduced
PeruPresentIntroduced
SurinamePresentIntroduced
VenezuelaPresentIntroduced

Risk of Introduction

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Although there is a risk of accidental introduction of C. canadensis, the fact that it is already so widespread means that the phytosanitary risk is relatively low. It is present in many regions where it is able to survive and grow and exclusion from other areas where it is not yet present may prove impossible. However, certain quarantine measures may ensure that it does not spread into certain specified areas within a country or region, such as protected areas. Being a weed of mainly undisturbed ground, the potential risks to such sites may be considerable.

Habitat

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C. canadensis is a weed of agriculture and forestry in temperate and subtropical climates and at higher elevations in some parts of the tropics. It is associated with perennial crops, fallows and field borders and, in annual crops, is favoured by reduced tillage. It is sometimes associated with sandy soils and irrigation, but is not limited to these conditions. It is also a weed of roadsides, old fields and is also associated with recently disturbed land, as an early successional species (Thebaud et al., 1996).

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial
Terrestrial ManagedCultivated / agricultural land Present, no further details Harmful (pest or invasive)
Terrestrial ManagedManaged forests, plantations and orchards Present, no further details Harmful (pest or invasive)
Terrestrial ManagedManaged grasslands (grazing systems) Present, no further details Harmful (pest or invasive)
Terrestrial ManagedDisturbed areas Present, no further details Harmful (pest or invasive)
Terrestrial ManagedRail / roadsides Present, no further details Harmful (pest or invasive)
Terrestrial Natural / Semi-naturalNatural forests Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

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C. canadensis occurs in a wide range of crops, annual and perennial, especially where tillage is less intensive. It has been reported in many orchard and other tree crops, including forestry, in grassland and forage crops, and also in annual crops being managed under minimal or reduced tillage regimes. It is also found as a weed in fields producing flowering bulbs and perennials, in forest nurseries, and in ornamental situations in turfgrass.

Biology and Ecology

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Genetics

C. canadensis is a diploid species, with a chromosome number of 2n=18. This is in contrast with several other species of Conyza, which were ascertained as allopolyploids (Thebaud and Abbot, 1995). As there is a tendency in plants to increasing ploidy levels, it may be assumed that C. canadensis is an ancestral member of the genus, and other species may have arisen via hybridization events. Chromosome size has been studied by Gosteva (1998).

Physiology and Phenology

C. canadensis is predominantly an annual plant, germinating in autumn and persisting as a rosette of leaves over the winter before bolting and flowering the following spring. It may, however, behave as a biennial in temperate climates, but rarely, if ever, persists for a second season after flowering. Seeds need a temperature of 10-25°C and require light for germination (Zinzolker et al., 1985). Establishment occurs mainly in occasionally disturbed situations. Intensive cultivations for annual crops apparently bury most of the seed and greatly reduce emergence, while in completely uncultivated situations other vegetation tends to interfere with its establishment (Escarré et al., 1998; Németh et al., 1998). After establishment as a rosette, elongation of the stem is inhibited by short days but occurs rapidly under longer day conditions (Zinzolker et al., 1985). For further information on the biology of C. canadensis, refer to Weaver (2001).

Reproductive Biology

Seed production can be immense, up to 250,000 seeds per plant (Holm et al., 1997; Weaver, 2001), and seed dispersal by wind is made highly efficient by the pappus (Weaver, 2001). Seed size is small, but also variable, with Fenner (1983) describing the rather complex relation between seed size, seedling establishment and vigour.

Environmental Requirements

C. canadensis is native to an area with a broad climatic amplitude, though is most common in temperate and mediterannean zones, it is found from tundra and taiga to the sub-tropics. Where introduced, it can even be found in tropical regions, though generally at higher altitudes.

There is little evidence for preference regarding soil type, with C. canadensis apparently able to grow in a wide range of soil types.

Associations

Prieur-Richard et al. (2002) studied in detail the invasion of C. bonariensis in Mediterranean annual plant communities (see the datasheet on C. bonariensis), though comparisons with C. canadensis may be invalid, as Conyza species are observed to have significantly different characteristics in terms of their position in plant succession. Nonetheless, Conyza spp. including C. canadensis are generally early successional species (e.g. Escarré et al., 1998), though Thebaud et al. (1996) noted that C. canadensis was restricted to recently disturbed areas, whereas C. sumatrensis colonized early- to mid-successional old fields. In Japan, they were noted as dominant in two-year-old fields, being able to grow as shade-tolerant rosettes under the canopy of other annuals, and being gradually succeeded by perennial grasses in later years (Ohtsuka, 1998).

Soil Tolerances

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Soil drainage

  • free
  • impeded

Soil reaction

  • acid
  • neutral

Soil texture

  • heavy
  • light
  • medium

Special soil tolerances

  • infertile
  • saline
  • shallow
  • sodic

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Basidiophora entospora Pathogen Plants|Leaves
Engyaulus pulchellus Herbivore Plants|Roots; Plants|Stems
Procecidochares australis Herbivore Plants|Stems
Uroleucon behuri Herbivore Plants|Leaves; Plants|Stems
Uroleucon erigeronense Herbivore Plants|Leaves; Plants|Stems

Means of Movement and Dispersal

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Natural Dispersal (Non-Biotic)

C. canadensis is principally a wind-dispersed species (e.g. Ohtsuka, 1998), facilitated by light seed accompanied by a pappus which aids flight.

Vector Transmission

No information is available on the possibility of spread by animals, but if it occurs, it is likely to be only of minor significance in comparison to wind-dispersal.

Agricultural Practices

C. canadensis is encouraged by irrigation, perhaps partly because of the distribution of seed by irrigation water (Holm et al., 1997). Mowing along roadsides, especially during seed production, is also likely to increase spread. Also, late tillage or other practices at such inappropriate times will also facilitate seed dispersal.

Accidental Introduction

Seed of several Conyza species now widely present as weeds outside of their native ranges were probably introduced to most of their introduced ranges accidentally as contaminants in cotton, cereals or forage grains/seed. The first appearance of C. bonariensis around textile mills in Europe and elsewhere where exotic means it may have been a contaminant of cotton, and seeds of other Conyza species may have been introduced via this pathway also. C. canadensis was considered by Park et al. (2001) to have been introduced into Korea Republic with imported cereals for concentrate feed or within seeds for forage production. This is a likely pathway, considering how the species is a weed in forage seed production stands, e.g. in lucerne (Dimitrova and Milanova, 2003).

Also a weed in nurseries, Conyza spp. may be spread as seed present in the soil in pots or other planting containers that accompany nursery stock, either as ornamentals (Gallitano and Skroch, 1993) or for establishing forest plantations (Prach et al., 1995). The spread of C. canadensis, along with numerous other weeds in central European forests, was thought to have been assisted by seeds in tree containers (Prach et al., 1995), and thus, presence in soil must be considered as a potential pathway.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Soil, sand and gravelSeeds in potting compost. Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Growing medium accompanying plants weeds/seeds Yes Pest or symptoms usually visible to the naked eye
True seeds (inc. grain) weeds/seeds Yes Pest or symptoms usually visible to the naked eye
Plant parts not known to carry the pest in trade/transport
Bark
Bulbs/Tubers/Corms/Rhizomes
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Leaves
Roots
Seedlings/Micropropagated plants
Stems (above ground)/Shoots/Trunks/Branches
Wood

Wood Packaging

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Wood Packaging not known to carry the pest in trade/transport
Loose wood packing material
Non-wood
Processed or treated wood
Solid wood packing material with bark
Solid wood packing material without bark

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) None
Crop production None
Environment (generally) None
Fisheries / aquaculture None
Forestry production None
Human health None
Livestock production None
Native fauna None
Native flora None
Rare/protected species None
Tourism None
Trade/international relations None
Transport/travel None

Impact

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Holm et al. (1997) record that C. canadensis occurs as a weed in 70 countries, in more than 40 crops. It is most common in the less intensively cultivated perennial crops, such as fruit orchards, vines, forestry, tea, grassland, sugarcane, pineapple and ornamental nurseries. It has also become increasingly important in zero-tilled annual crops, such as cotton and soyabean, where the seeds are left on the soil surface and are exposed to the light necessary for germination, and are not controlled by normal pre-planting tillage (Buhler and Owen, 1997). Having germinated in the autumn it is often well grown by the time of planting and thus quite difficult to control. Its importance is increased by its widespread resistance to paraquat and triazines (see Chemical Control). The are few estimates of its competitive effect, but in Romania yield reductions of 64% have been recorded in sugar beet (Sarpe and Torge, 1980) and Holm et al. (1997) note that vegetative growth of vines can be reduced by 28%. There are some reports of damaging allelopathic effects, for example, to Trifolium repens and lettuce (Souto et al., 1990) It may cause additional economic damage as a result of its aromatic oils contaminating those harvested from Mentha spp. (Ogg et al., 1975).

It is recorded as an alternative host of Tomato bushy stunt virus (Grbelja et al., 1988), and as a host for numerous other serious plant viruses including Tomato spotted wilt virus and Cucumber mosaic virus, nematodes such as Meloidogyne javanica (Dahiya et al., 1998) and Rotylenchulus reniformis (Wang et al., 2003), fungal pathogens such as Sclerotinia minor, also aster yellows phytoplasma, and a range of insect pests (e.g. Weaver, 2001).

Environmental Impact

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The presence of C. canadensis is seen to have significant effects on the soil carbon:nitrogen ratio in a subtropical orchard (Chen et al., 2004), and as such can be expected to have similar effects on natural ecosystems if it become invasive there, though the actual importance of any changes to soil have yet to be ascertained in such situations.

Risk and Impact Factors

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Invasiveness
  • Proved invasive outside its native range
  • Highly adaptable to different environments
  • Highly mobile locally
  • Has high reproductive potential
Impact outcomes
  • Negatively impacts agriculture
Impact mechanisms
  • Competition - monopolizing resources
  • Pest and disease transmission
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult/costly to control

Uses

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In Japan and China, the essential oils from C. canadensis are used in the treatment of jaundice (Miyazawa et al., 1992), and the oils have been observed to have antifungal effects. Also, plant extracts have some antifeedant effects on insect species, and as such have potential use as repellents in stored grains. There are also some reports of suppression of other weeds, which could perhaps be regarded as beneficial (Varadi et al., 1987).

Uses List

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Materials

  • Essential oils

Medicinal, pharmaceutical

  • Traditional/folklore

Similarities to Other Species/Conditions

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Several other Conyza spp. are common weeds, overlapping with C. canadensis in distribution, but these are generally distinguished by having more finely hairy, greyish-green foliage, without the scattered long marginal hairs, and flower heads without ray florets (see datasheets on C. bonariensis and C. sumatrensis). See also Reutelingsperger (2000) for a key differentiating these species.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control

In traditional farming, C. canadensis is controlled satisfactorily by tillage, hand-weeding and also suitable crop rotation (e.g. Leroux et al., 1996). In more developed systems, non-chemical methods include the use of living mulches of, for example, Trifolium subterraneum (Enache and Ilnicki, 1988). Other mulches, living or inert, are observed to increase control of C. canadensis, which may be expected as seeds require light for germination. The use of cover crops may also have a similar effect, due to direct competition for light and possible water and plant nutrients, and were shown to be effective in controlling C. canadensis in apple orchards in Korea (Jung et al., 1998). It is, however, surprisingly resistant to destruction by soil solarization (Horowitz et al., 1983).

Chemical Control

C. canadensis is normally susceptible to most of the herbicides used to control annual broad-leaved weeds, including 2,4-D and dicamba. However, it has developed widespread resistance to paraquat and the triazines in Europe and the USA. The mechanisms of resistance have been studied in detail, including the dual resistance to both herbicide groups in Hungary (Polos et al., 1988; Lehoczki et al., 1992; Darko et al., 1996). Paraquat resistance has been shown to be controlled by a single dominant gene (Yamasue et al., 1992). This resistance automatically confers moderate resistance to diquat, and triazine resistance results in less susceptibility to bromacil and lenacil. Linuron resistance is also reported from France (Beuret, 1988) and terbacil resistance in Hungary (Molnar et al., 1988). One previously isolated report of resistance to glyphosate (Talbert et al., 1975) is now supported by others, e.g. Solymosi (2001) in Hungary and Van Gessel (2001) in the USA, confirming the increased resistance of this species to such herbicides normally effective along with a wide range of other alternatives depending on the particular cropping regime. These include sulfonylurea herbicides (Németh et al., 1998), cyanazine, sulfallate, glufosinate, oxyfluorfen, hexazinone, tebuthiuron, amitrole, asulam, oryzalin, clopyralid and imazapyr. Inconsistent results are reported with diuron, metribuzin, bentazon and acifluorfen, while poor results have been reported with oxadiazon and imazethapyr.

Biological Control

There has been consideration of biological control possibilities in Italy (Pecora, 1977), the insects of interest including the tephritid Procecidochares australis from USA and the coleopteran Agrilus pulchellus [Engyaulus pulchellus] which is known to attack other Conyza/Erigeron species; but there are no reports of any practical progress.

References

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Baliousis E, 2014. Recent data from the flora of the island of Limnos (NE Aegean, Greece): new alien invasive species affecting the agricultural economy of the island. Edinburgh Journal of Botany, 71(2):275-285. http://www.journals.cup.org/action/displayJournal?jid=EJB

Bebawi FF; Neugebohrn L, 1991. A review of plants of northern Sudan with special reference to their uses. A review of plants of northern Sudan with special reference to their uses., 294pp.; [many col. pl., 1 map]; 10 ref.

Beuret E, 1988. Peculiar feature of resistance to atrazine and linuron in Amaranthus lividus L. and Erigeron canadensis L. VIIIe Colloque International sur la Biologie, l'Ecologie et la Systematique des Mauvaises Herbes. Paris, France: A.N.P.P., Vol. 1:277-286.

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Chen X; Tang JJ; Fang ZG, 2004. Effects of weed communities with various species numbers on soil features in a subtropical orchard ecosystem. Agriculture, Ecosystems and Environment, 102(3):377-388.

Cronquist A, 1976. Conyza Less. In: Tutin TG, Heywood VH, Burges NA, Moore DM, Valentine DH, Walters SM, Webb DA, eds. Flora Europaea, Volume 4, Plantaginaceae to Compositae (and Rubiaceae). Cambridge, UK: Cambridge University Press.

Dahiya RS; Mangat BPS; Bhatti DS, 1988. Some new host records of Meloidogyne javanica. International Nematology Network Newsletter, 5(3):32-34.

Dark= T; Vßradi G; Dulai S; Lehoczki E, 1996. Atrazine-resistant biotypes of Conyza canadensis have altered fluorescence quenching and xanthophyll cycle pattern. Plant Physiology and Biochemistry (Paris), 34(6):843-852; 46 ref.

Dimitrova T; Milanova S, 2003. Control of Canadian fleabane (erigeron canadensis L.) in seed production stands of Lucerne (Medicago sativa L.). Bulgarian Journal of Agricultural Science, 9(3):349-352.

Enache A; Ilnicki RD, 1988. Subterranean clover: a new approach to weed control. Proceedings of the 42nd annual meeting of the Northeastern Weed Science Society, 34.

EscarrT J; Debussche M; Imbert E; Lepart J; ThTbaud C, 1998. Life history traits of three exotic invasive Compositae: Conyza canadensis, Conyza sumatrensis and Crepis sancta. Comptes-rendus 6e^grave~me Symposium Me^acute~diterrane^acute~en EWRS, Montpellier, France, 13-15 Mai 1998., 11-17; 28 ref.

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Gosteva EV, 1998. Densitometric scanning of plant chromosomes for their identification. Tsitologiya i Genetika, 32(5):17-21; 11 ref.

Grbelja J; Eric Z; Jeknic Z, 1988. Erigeron canadensis L. - a potential source of infection by the tomato bushy stunt virus for cultivated plants. Fragmenta Herbologica Jugoslavica, 17(1-2):95-99.

Henty EE; Pritchard GH, 1975. Weeds of New Guinea and their Control. Lp, Papua New Guinea: Department of Forests, Division of Botany, Botany Bulletin No.7.

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Jung JS; Lee JS; Choi CD; Cheung JD, 1998. A study on sod culture using water foxtail (Alopecurus aequalis var. amurensis) in apple orchard. Korean Journal of Weed Science, 18(2):128-135; 17 ref.

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Leroux GD; Ben(it DL; Banville S, 1996. Effect of crop rotations on weed control, Bidens cernua and Erigeron canadensis populations, and carrot yields in organic soils. Crop Protection, 15(2):171-178; 20 ref.

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Polos E; Mikulas J; Szigeti Z; Matkovics B; Hai DQ; Parducz A; Lehoczki E, 1988. Paraquat and atrazine co-resistance in Conyza canadensis (L.) Cronq. Pesticide Biochemistry and Physiology, 30(2):142-154

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Souto XC; Gonzalez L; Reigosa MJ, 1990. Preliminary study of the allelopathic potential of twelve weed species. Actas de la Reunion de la Sociedad Espanola de Malherbologia, 199-206.

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Thebaud C; Abbott RJ, 1995. Characterization of invasive Conyza species (Asteraceae) in Europe: quantitative trait and isozyme analysis. American Journal of Botany, 82(3):360-368.

Thebaud C; Finzi AC; Affre L; Debussche M; Escarre J, 1996. Assessing why two introduced Conyza differ in their ability to invade Mediterranean old fields. Ecology, 77(3):791-804.

USDA-ARS, 2004. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch.aspx

VanGessel MJ, 2001. Glyphosate-resistant horseweed from Delaware. Weed Science, 49(6):703-705; 14 ref.

Varadi G; Mikulas J; Polos E, 1987. Allelopathy of weeds in vineyards. Proceedings of the 1987 British Crop Protection Conference, Weeds, Vol.2:671-678.

Wang KH; Sipes BS; Schmitt DP, 2003. Intercropping cover crops with pineapple for the management of Rotylenchulus reniformis. Journal of Nematology, 35(1):39-47.

Wang ZR, 1990. Farmland Weeds in China. Beijing, China: Agricultural Publishing House.

Weaver SE, 2001. The biology of Canadian weeds. 115. Conyza canadensis. Canadian Journal of Plant Science, 81(4):867-875; many ref.

Wells MJ; Balsinhas AA; Joffe H; Engelbrecht VM; Harding G; Stirton CH, 1986. A catalogue of problem plants in South Africa. Memoirs of the botanical survey of South Africa No 53. Pretoria, South Africa: Botanical Research Institute.

Whittle CA; Duchesne LC; Needham T, 1997. The impact of broadcast burning and fire severity on species composition and abundance of surface vegetation in a jack pine (Pinus banksiana) clear-cut. Forest Ecology and Management, 94(1/3):141-148; 33 ref.

Yamasue Y; Kamiyama K; Hanioka Y; Kusanagi T, 1992. Paraquat resistance and its inheritance in seed germination of the foliar-resistant biotypes of Erigeron canadensis L. and E. sumatrensis Retz. Pesticide Biochemistry and Physiology, 44(1):21-27.

Zinzolker A; Kigel J; Rubin B, 1985. Effects of environmental factors on the germination and flowering of Conyza albida, C. bonariensis and C. canadensis. Phytoparasitica, 13(3/4):229-230.

Distribution References

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