HRAC GROUP 2 (LEGACY B) RESISTANT THREEHORN BEDSTRAW
(Galium tricornutum)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Australia, South Australia

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INTRODUCTION THREEHORN BEDSTRAW Threehorn Bedstraw (Galium tricornutum) is a dicot weed in the Rubiaceae family.  In South Australia this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2012 and infests Spring Barley, and Wheat.   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 imazamox, imazapyr, iodosulfuron-methyl-Na, and pyroxsulam 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 21, 2014 ) Common Name Threehorn Bedstraw Species Galium tricornutum Group Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B) Herbicides imazamox, imazapyr, iodosulfuron-methyl-Na, and pyroxsulam Location Australia, South Australia Year 2012 Situation(s) Spring Barley, and Wheat Contributors - (Alphabetically) Peter Boutsalis, and Christopher Preston  Edit this Case  |  Add New Case of Resistance  |  Add Note

ACADEMIC ASPECTS Confirmation Tests Greenhouse, and Laboratory trials comparing a known susceptible Threehorn Bedstraw biotype with this Threehorn Bedstraw 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 Threehorn Bedstraw 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 Threehorn Bedstraw from South Australia please update the database.   Edit Case  |  Add Note  |  Add Article  |  Add New Case  |  Help

CONTRIBUTING WEED SCIENTISTS PETER BOUTSALIS Postdoctural Fellow/ Consultant University Of Adelaide / Plant Science Consulting Plant And Pest Science 800 N Lindbergh Blvd 02G Adelaide, 5064, South Australia Australia Email Peter Boutsalis CHRISTOPHER PRESTON Postdoctural Fellow/ Consultant University Of Adelaide - Waite Campus Crc For Australian Weed Management And School Of Agriculture Box 2146 Adelaide, 5064, South Australia Australia Email Christopher Preston

ACKNOWLEDGEMENTS The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in South Australia have been instrumental in providing you this information. Particular thanks is given to Peter Boutsalis, and Christopher Preston for providing detailed information.

Herbicide Resistant Threehorn Bedstraw Globally (Galium tricornutum) Herbicide Resistant Threehorn Bedstraw Globally (Galium tricornutum) Drag a column header and drop it here to group by that column Herbicide Resistant Threehorn Bedstraw Globally (Galium tricornutum) # Country Country StateName FirstYear Situation Active Ingredients CountryID Site of Action WeedID Species CommonName ResistID 1 Australia (South Australia) Australia South Australia 2012 Spring Barley, and Wheat imazamox, imazapyr, iodosulfuron-methyl-Na, and pyroxsulam 1 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B) 306 Galium tricornutum Threehorn Bedstraw 7837

Literature about Similar Cases

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Moerkerk, M. R.. 1999. Chemical control of bedstraw (Galium tricornutum Dandy) in wheat, barley, field peas, chickpeas and faba beans in southern Australia. Plant Protection Quarterly 14 : 24 - 29.

Field experiments were carried out in Victoria between 1991 and 1994 to assess the efficacy of selective herbicides for the control of bedstraw in commercial field crops, Imazethapyr provided acceptable control of bedstraw in faba beans, field peas and chickpeas when applied pre-emergence, and in field peas post-emergence. Chickpea and faba beans were intolerant to imazethapyr applied post-emergence. Flumetsulam applied post-emergence gave effective control of bedstraw seed production in chickpeas and field peas. Faba beans were intolerant to flumetsulam. Bentazone, pyridate, diflufenican, simazine and metribuzin failed to give adequate control of bedstraw in pulse crops. In wheat and barley, chemicals applied early post-emergence that provided acceptable crop safety and control bedstraw included bromoxynil + MCPA ester + dicamba, flumetsulam, bromoxynil + diflufenican, fluroxypyr and amidosulfuron. Metsulfuron-methyl, metsulfuron-methyl + bromoxynil + MCPA ester, bromoxynil + MCPA ester and chlorsulfuron did not consistently control bedstraw in cereals. Bedstraw could be effectively controlled at later cereal growth stages with 2,4-D amine or fluroxypyr. Yield responses to chemical control of bedstraw were greater with herbicide applied earlier than later in the growing season. The implication of chemical control options on potential herbicide resistance development in bedstraw is discussed..

Black, I. D. ; Mayfield, A. ; Matic, R.. 1994. Chemical control of bedstraw (Galium tricornutum Dandy) and bifora (Bifora testiculata L.) in wheat, barley and field peas. Plant Protection Quarterly 9 : 24 - 27.

In field trials conducted on the Yorke Peninsula in South Australia during 1986-91, the effects were evaluated of 13 selective herbicides for the control of G. tricornutum and B. testiculata in wheat, barley and peas. When applied early post-em. or at the early tillering stage of wheat or barley, fluroxypyr at 175-250 g/ha, dicamba at 140 g, dicamba + MCPA ester at 112 + 476 g, dicamba + bromoxynil + MCPA ester at 56 + 196 + 392 g, chlorsulfuron at 19 g, triasulfuron + terbutryn at 10 + 300 g and diflufenican + MCPA ester at 25 + 250 g controlled G. tricornutum, on av., by ≥90% and resulted in crop yields of 98-128% of the untreated controls. Imazethapyr at 20-100 g applied post-plant pre-em. or early post-em., metribuzin + imazethapyr at 146-197 + 20 g applied early post-em., and flumetsulam at 20 g applied early or later post-em. were the most effective treatments for the control of G. tricornutum in peas (80-90% control). However, crop tolerance of the flumetsulam treatments was marginal, especially following the earlier application date. When applied early post-em. to wheat or barley, chlorsulfuron at 15 g or triasulfuron at 26 g + bromoxynil + MCPA ester (both at 140 g) and metsulfuron-methyl + diuron + MCPA ester (at 4 + 250 + 175 g) provided ≥90% control of B. testiculata. Crop tolerance was satisfactory, except for metsulfuron-methyl + diuron + MCPA ester, and for the high concn of metribuzin in wheat. Imazethapyr (at 60-100 g) and metribuzin (at 210-290 g) applied early post-em. and cyanazine (750-1000 g) applied early or later post-em. were the most effective treatments for the control of B. testiculata in peas (80-90% control). Crop tolerance was acceptable except for some cyanazine treatments and some of the higher concn of metribuzin..

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