(Arctotheca calendula)

Multiple Resistance: 3 Sites of Action
ALS inhibitors (B/2)
Phytoene Desaturase inhibitors (F1/12)
EPSP synthase inhibitors (G/9)

Australia, Western Australia
Capeweed (Arctotheca calendula) is a dicot weed in the Asteraceae family.  In Western Australia this weed first evolved multiple resistance (to 3 herbicide sites of action) in 2020 and infests Wheat.  Multiple resistance has evolved to herbicides in the Groups B/2, F1/12, and G/9.  These particular biotypes are known to have resistance to diflufenican, glyphosate, and metosulam and they may be cross-resistant to other herbicides in the Groups B/2, F1/12, and G/9.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

If we do not have a picture for this weed, or you can provide a better picture (scan, digital camera etc) please please e-mail it to us.

QUIK STATS (last updated Feb 26, 2021 )

Common NameCapeweed
SpeciesArctotheca calendula
GroupALS inhibitors (B/2)
Phytoene Desaturase inhibitors (F1/12)
EPSP synthase inhibitors (G/9)
Herbicidesdiflufenican, glyphosate, and metosulam
LocationAustralia, Western Australia
Contributors - (Alphabetically)Michael Ashworth, Hugh Beckie, and Heping Han 
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Pest Management Science 2021.  DOI 10.1002/ps.6295 

Identification of the first glyphosate-resistant capeweed (Arctotheca calendula) population

 Yaseen Khalil,a* Michael B Ashworth,a Heping Han,a Yu Qin,a Roberto L Rocha,a Brent Pritchard,b David Cameronc and Hugh J Beckiea Abstract


BACKGROUND: Glyphosate is routinely used in Australia to control the Arctotheca species Arctotheca calendula (L.) Levyns (referred hereinafter as capeweed). This study identifies the first global case of field-evolved glyphosate-resistant capeweed, collected from the grainbelt of Western Australia.

RESULTS: In 2020, a capeweed biotype that was collected from Borden in the southern Western Australian grainbelt was confirmed to be glyphosate-resistant (referred hereinafter as Spence population). When compared to the pooled mortality of six field-collected, glyphosate susceptible capeweed populations (S1, S2, S3, S4, S5 and S6), the Spence population was found > 11-fold more resistant to glyphosate than the pooled results of the susceptible populations (S1–S6) at the lethal dose of 50% (LD50) level. The growth of the Spence population was also less affected, requiring > 13-fold more glyphosate to reduce growth than the pooled susceptible populations at the growth reduction of 50% (GR50) level. Sequencing of the plastidic 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene indicated no known single gene mutation imparting glyphosate resistance. This study, however, did not investigate any other known mechanisms that impart glyphosate resistance. When screened at the field-applied rate, this Spence population was also found to survive an inhibitor of acetolactate synthase (ALS) (metosulam) and an inhibitor of phytoene desaturase (diflufenican).

CONCLUSIONS: This is the first confirmation of glyphosate resistance evolution in a capeweed population globally. With capeweed resistance already confirmed to photosystem-I inhibiting herbicides (paraquat and diquat), this study emphasizes the importance of using integrated measures that do not depend only on the use of non-selective herbicides for controlling herbicide resistance-prone capeweed populations. © 2021 Society of Chemical Industry

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Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Capeweed biotype with this Capeweed biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetic studies on Group B, F1, G/2, 12, 9 resistant Capeweed have not been reported to the site.  There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature
Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database.  If you know anything about the mechanism of resistance for this biotype then please update the database.
Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes.  If you have any information pertaining to the fitness of multiple resistant Capeweed from Western Australia please update the database.
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PhD Student
University of Western Australia, School of Botany
Australian Herbicide Resistance Initiative
University of Western Australia
Crawley, 6009, Western Australia
Email Michael Ashworth
Web   : Web Site Link
Research Scientist
Agriculture & Agri-Food Canada, Science & Technology Branch
Herbicide-Resistant & Novel-Trait Plants
107 Science Place
Saskatoon, S7N 0X2, Saskatchewan
Email Hugh Beckie
Web   : Web Site Link
Research associate
Australian herbicide resistance initiative
University of Aestern Australia
Perth, 6009, Western Australia
Email Heping Han
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Western Australia have been instrumental in providing you this information. Particular thanks is given to Michael Ashworth, Hugh Beckie, and Heping Han for providing detailed information.
Herbicide Resistant Capeweed Globally
(Arctotheca calendula)
Herbicide Resistant Capeweed Globally
(Arctotheca calendula)
Drag a column header and drop it here to group by that column
Herbicide Resistant Capeweed Globally
(Arctotheca calendula)
#CountryFirstYearSituationActive IngredientsSite of Action
1 Australia (Victoria) AustraliaVictoria1986 Alfalfa diquat 1 PSI Electron Diverter (D/22)
21Arctotheca calendulaCapeweed22
2 Australia (South Australia) AustraliaSouth Australia2015 Fallow 2,4-D 1 Auxin Mimics (O/4)
21Arctotheca calendulaCapeweed15055
3 Australia (Western Australia) AustraliaWestern Australia2020 Wheat diflufenican, glyphosate, and metosulam 1 Multiple Resistance: 3 Sites of Action
ALS inhibitors (B/2)
Phytoene Desaturase inhibitors (F1/12)
EPSP synthase inhibitors (G/9)
21Arctotheca calendulaCapeweed19216
Literature about Similar Cases

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PERMISSION MUST BE OBTAINED FIRST if you intend to base a significant portion of a scientific paper on data derived from this site. Citation:
Heap, I.  The International Herbicide-Resistant Weed Database.  Online.  Saturday, April 10, 2021 .  Available Copyright © 1993- 2021 All rights reserved. Fair use of this material is encouraged. Proper citation is requested.