<b>HRAC Group 2</b> <font size='2'> (Legacy B) </font> resistant Helianthus annuus from United States, Iowa

International Survey of Herbicide-Resistant Weeds

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Tuesday, November 26, 2024

HRAC GROUP 2 (LEGACY B) RESISTANT COMMON SUNFLOWER
(Helianthus annuus)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

United States, Iowa

INTRODUCTION		COMMON SUNFLOWER
Common Sunflower (Helianthus annuus) is a dicot weed in the Asteraceae family. In Iowa this weed first evolved resistance to Group 2 (Legacy B) herbicides in 1997 and infests Corn (maize), and Soybean. Group 2 (Legacy B) herbicides are known as Inhibition of Acetolactate Synthase (Inhibition of Acetolactate Synthase ). Research has shown that these particular biotypes are resistant to chlorimuron-ethyl, and imazethapyr and they may be cross-resistant to other Group 2 (Legacy B) 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 Jan 15, 2010 )
Common Name	Common Sunflower
Species	Helianthus annuus
Group	Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicides	chlorimuron-ethyl, and imazethapyr
Location	United States, Iowa
Year	1997
Situation(s)	Corn (maize), and Soybean
Contributors - (Alphabetically)	Robert Hartzler, and Ian Zelaya
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NOTES ABOUT THIS BIOTYPE

GENERAL

Ian Zelaya

The resistant common sunflower biotype was collected in Cherokee, IA. Greenhouse and laboratory studies confirmed that the Cherokee, IA biotype was cross-resistant to imazethapyr (GR50 R:S ratio = 36) and chlorimuron-ethyl (GR50 R:S ratio = 43). The susceptible common sunflower biotype was collected at Woodruff Farm in Ames, IA. Source: Zelaya, I. A., and M. D. K. Owen. 2004. Evolved resistance to acetolactate synthase-inhibiting herbicides in common sunflower (Helianthus annuus), giant ragweed (Ambrosia trifida), and shattercane (Sorghum bicolor) in Iowa. Weed Science 52:538-548.

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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Common Sunflower biotype with this Common Sunflower 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 2 resistant Common Sunflower 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 2 (Legacy B) resistant Common Sunflower from Iowa please update the database.

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CONTRIBUTING WEED SCIENTISTS

ROBERT HARTZLER

Extension Weed Specialist and Professor of Agronomy Iowa State University Weed Science 2104 Agronomy Hall Ames, 50011, Iowa United States Email Robert Hartzler Web : Web Site Link

IAN ZELAYA

Extension Weed Specialist and Professor of Agronomy Syngenta Weed Control Unit Carrera 7 No. 113-43 Piso 10 Bogotá, 50011, Iowa Colombia Email Ian Zelaya Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Iowa have been instrumental in providing you this information. Particular thanks is given to Robert Hartzler, and Ian Zelaya for providing detailed information.

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Herbicide Resistant Common Sunflower Globally
(Helianthus annuus)

Country

FirstYear

Situation

Active Ingredients

Site of Action

France

2009

Sunflower

imazamox, and tribenuron-methyl