HRAC GROUP 4 (LEGACY O) RESISTANT ITALIAN THISTLE
(Carduus pycnocephalus)

Auxin Mimics HRAC Group 4 (Legacy O)

New Zealand

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INTRODUCTION ITALIAN THISTLE Italian Thistle (Carduus pycnocephalus) is a dicot weed in the Asteraceae family.  In New Zealand this weed first evolved resistance to Group 4 (Legacy O) herbicides in 1997 and infests Pastures.   Group 4 (Legacy O) herbicides are known as Auxin Mimics (Auxin Mimics ).  Research has shown that these particular biotypes are resistant to 2,4-D, MCPA, and MCPB and they may be cross-resistant to other Group 4 (Legacy O) 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.

QUIK STATS (last updated Dec 13, 2013 ) Common Name Italian Thistle Species Carduus pycnocephalus Group Auxin Mimics HRAC Group 4 (Legacy O) Herbicides 2,4-D, MCPA, and MCPB Location New Zealand Year 1997 Situation(s) Pastures Contributors - (Alphabetically) Kerry Harrington  Edit this Case  |  Add New Case of Resistance  |  Add Note

ACADEMIC ASPECTS Confirmation Tests Field, and Greenhouse trials comparing a known susceptible Italian Thistle biotype with this Italian Thistle biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.   Genetics Genetic studies on HRAC Group 4 resistant Italian Thistle 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 4 (Legacy O) resistant Italian Thistle from New Zealand please update the database.   Edit Case  |  Add Note  |  Add Article  |  Add New Case  |  Help

CONTRIBUTING WEED SCIENTISTS KERRY HARRINGTON Associate Professor in Weed Science Massey University School of Agriculture Private Bag 11-222 Palmerston North, 4442, Manawatu New Zealand Email Kerry Harrington Web   : Web Site Link

ACKNOWLEDGEMENTS The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in New Zealand have been instrumental in providing you this information. Particular thanks is given to Kerry Harrington for providing detailed information.

Herbicide Resistant Italian Thistle Globally (Carduus pycnocephalus) Herbicide Resistant Italian Thistle Globally (Carduus pycnocephalus) Drag a column header and drop it here to group by that column Herbicide Resistant Italian Thistle Globally (Carduus pycnocephalus) # Country Country StateName FirstYear Situation Active Ingredients CountryID Site of Action WeedID Species CommonName ResistID 1 New Zealand New Zealand   1997 Pastures 2,4-D, MCPA, and MCPB 30 Auxin Mimics ( HRAC Group 4 (Legacy O) 43 Carduus pycnocephalus Italian Thistle 513

Literature about Similar Cases

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Harrington, K. C.. 1989. Distribution and cross-tolerance of MCPA-tolerant nodding thistle. : 39 - 42.

By using petri dish assays and collected seeds, at least 12 new sites were identified in Hawkes Bay and Waikato where nodding thistle (Carduus nutans) showed tolerance to MCPA at 1.1 kg/ha. Slender winged thistle (Carduus pycnocephalus) showed a similar level of tolerance at the one site at which it was studied. Tolerance by nodding thistle of other herbicides, especially MCPB at 2.4 kg and 2,4-D at 1.1 kg was also shown..

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