International Survey of Herbicide-Resistant Weeds

Countries Weeds Herbicides Mutations Graphs References Researchers
(Centaurea stoebe ssp. micranthos)

Synthetic Auxins (O/4)

Canada, British Columbia
Spotted knapweed (Centaurea stoebe ssp. micranthos) is a dicot weed in the Asteraceae family.  In British Columbia this weed first evolved resistance to Group O/4 herbicides in 2013 and infests Rangeland.   Group O/4 herbicides are known as Synthetic Auxins (Synthetic auxins (action like indoleacetic acid)).  Research has shown that these particular biotypes are resistant to clopyralid, and picloram and they may be cross-resistant to other Group O/4 herbicides.

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 Dec 16, 2016 )

Common NameSpotted knapweed
SpeciesCentaurea stoebe ssp. micranthos
GroupSynthetic Auxins (O/4)
Herbicidesclopyralid, and picloram
LocationCanada, British Columbia
Contributors - (Alphabetically)Linda Hall, and Amy Mangin 
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Amy Mangin

Can. J. Plant Sci. 00: 1–4 (0000)

First report: spotted knapweed (Centaurea stoebe) resistance to auxinic herbicides

Amy R. Mangin and Linda M. Hall

Abstract: Spotted knapweed is a prohibited noxious weed that is primarily controlled with auxinic herbicides. A population collected from a managed rangeland in East Kootenay, BC, was highly resistant to both clopyralid and picloram, with R/S ratios of >25 600 and 28, respectively. This is the first report of resistance in spotted knapweed.

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Confirmation Tests

Greenhouse trials comparing a known susceptible Spotted knapweed biotype with this Spotted knapweed 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 O/4 resistant Spotted knapweed 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 Group O/4 resistant Spotted knapweed from British Columbia please update the database.
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Alberta Agriculture
Plant Industry Division
Agronomy Unit
4550 New Linden Hill Rd
Ste 501,
Edmonton, T6H 5Z2, Alberta
Email Linda Hall
Graduate Student
University of Alberta
Food and Nutritional Sciences
410 Agriculture/Forestry Centre
Edmonton, T6G 2E1, Alberta
Email Amy Mangin


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in British Columbia have been instrumental in providing you this information. Particular thanks is given to Linda Hall, and Amy Mangin for providing detailed information.
Herbicide Resistant Spotted knapweed Globally
(Centaurea stoebe ssp. micranthos)
Herbicide Resistant Spotted knapweed Globally
(Centaurea stoebe ssp. micranthos)
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Herbicide Resistant Spotted knapweed Globally
(Centaurea stoebe ssp. micranthos)
#CountryFirstYearSituationActive IngredientsSite of Action
1 Canada (British Columbia) CanadaBritish Columbia2013 Rangeland clopyralid, and picloram 7 Synthetic Auxins (O/4)
334Centaurea stoebe ssp. micranthosSpotted knapweed15061
Literature about Similar Cases

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Cite this site as: Heap, I.  The International Survey of Herbicide Resistant Weeds.  Online.  Internet.  Sunday, March 18, 2018 .  Available
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