HRAC GROUP 5 (LEGACY C1 C2) RESISTANT SQUIRRELTAIL FESCUE
(Vulpia bromoides)

PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)

Australia, Western Australia

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INTRODUCTION SQUIRRELTAIL FESCUE Squirreltail Fescue (Vulpia bromoides) is a monocot weed in the Poaceae family.  In Western Australia this weed first evolved resistance to Group 5 (Legacy C1 C2) herbicides in 2014 and infests Pastures.   Group 5 (Legacy C1 C2) herbicides are known as PSII inhibitors - Serine 264 Binders (Inhbition of Photosynthesis at PSll - Serine 264 Binders ).  Research has shown that these particular biotypes are resistant to simazine and they may be cross-resistant to other Group 5 (Legacy C1 C2) 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 Feb 06, 2016 ) Common Name Squirreltail Fescue Species Vulpia bromoides Group PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2) Herbicides simazine Location Australia, Western Australia Year 2014 Situation(s) Pastures Contributors - (Alphabetically) Michael Ashworth, and Stephen Powles  Edit this Case  |  Add New Case of Resistance  |  Add Note

ACADEMIC ASPECTS Confirmation Tests Greenhouse, and Laboratory trials comparing a known susceptible Squirreltail Fescue biotype with this Squirreltail Fescue 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 5 resistant Squirreltail Fescue 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 Studies on the mechanism of resistance of Group 5 (Legacy C1 C2) resistant Squirreltail Fescue from Western Australia indicate that resistance is due to an altered target site.  There may be a note below or an article discussing the mechanism of resistance in the Fact Sheets and Other Literature   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 5 (Legacy C1 C2) resistant Squirreltail Fescue from Western Australia please update the database.   Edit Case  |  Add Note  |  Add Article  |  Add New Case  |  Help

CONTRIBUTING WEED SCIENTISTS MICHAEL ASHWORTH PhD Student University of Western Australia, School of Botany Australian Herbicide Resistance Initiative University of Western Australia Crawley, 6009, Western Australia Australia Email Michael Ashworth Web   : Web Site Link STEPHEN POWLES Professor And Research Director University Of Western Australia School Of Plant Biology 2276 Dahlk Circle Crawley, 6009, Western Australia Australia Email Stephen Powles Web   : Web Site Link

ACKNOWLEDGEMENTS 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, and Stephen Powles for providing detailed information.

Herbicide Resistant Squirreltail Fescue Globally (Vulpia bromoides) Herbicide Resistant Squirreltail Fescue Globally (Vulpia bromoides) Drag a column header and drop it here to group by that column Herbicide Resistant Squirreltail Fescue Globally (Vulpia bromoides) # Country Country StateName FirstYear Situation Active Ingredients CountryID Site of Action WeedID Species CommonName ResistID 1 Australia (Victoria) Australia Victoria 1990 Alfalfa diquat, and paraquat 1 PS I Electron Diversion ( HRAC Group 22 (Legacy D) 173 Vulpia bromoides Squirreltail Fescue 17 2 Australia (Victoria) Australia Victoria 2009 Pastures simazine 1 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2) 173 Vulpia bromoides Squirreltail Fescue 7841 3 Australia (Western Australia) Australia Western Australia 2014 Pastures simazine 1 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2) 173 Vulpia bromoides Squirreltail Fescue 11030

Literature about Similar Cases

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Yu Qin ; Friesen, L. J. S. ; Zhang XiaoQi ; Powles, S. B.. 2004. Tolerance to acetolactate synthase and acetyl-coenzyme A carboxylase inhibiting herbicides in Vulpia bromoides is conferred by two co-existing resistance mechanisms. Pesticide Biochemistry and Physiology 78 : 21 - 30.

Vulpia bromoides is a grass species naturally tolerant to acetolactate synthase (ALS) and acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides. The mechanism of tolerance to ALS herbicides was determined as cytochrome P450-monooxygenase mediated metabolic detoxification. The ALS enzyme extract partially purified from V. bromoides shoot tissue was found to be as sensitive as that of herbicide susceptible Lolium rigidum to ALS-inhibiting sulfonylurea (SU), triazolopyrimidine (TP), and imidazolinone (IM) herbicides. Furthermore, phytotoxicity of the wheat-selective SU herbicide chlorsulfuron was significantly enhanced in vivo in the presence of the known P450 inhibitor malathion. In contract, the biochemical basis of tolerance to ACCase inhibiting herbicides was established as an insensitive ACCase. In vitro ACCase inhibition assays showed that, compared to a herbicide susceptible L. rigidum, the V. bromoides ACCase was moderately (4.5- to 9.5-fold) insensitive to the aryloxyphenoxypropionate (APP) herbicides diclofop, fluazifop, and haloxyfop and highly insensitive (20- to >71-fold) to the cyclohexanedione (CHD) herbicides sethoxydim and tralkoxydim. No differential absorption or de-esterification of fluazifop-P-butyl was observed between the two species at 48 h after herbicide application, and furthermore V. bromoides did not detoxify fluazifop acid as rapidly as susceptible L. rigidum. It is concluded that two co-existing resistance mechanisms, i.e., an enhanced metabolism of ALS herbicides and an insensitive target ACCase, endow natural tolerance to ALS and ACCase inhibiting herbicides in V. bromoides..

Purba, E. ; Preston, C. ; Powles, S. B.. 1993. Paraquat resistance in a biotype of Vulpia bromoides (L.) S. F. Gray. Weed Research (Oxford) 33 : 409 - 413.

Laboratory experiments were conducted to study a biotype of V. bromoides which had survived field applications of 125 g/ha paraquat and 75 g diquat in a lucerne field at Elmhurst, Victoria. Pot-grown resistant and a susceptible biotypes of V. bromoides were sprayed with paraquat at concn of 12.5-800 g and diquat at 25-800 g. Applications of paraquat at 50 g killed all of the susceptible V. bromoides plants but only 6% of the resistant biotype. The LD₅₀ for paraquat of the resistant biotype was 5- to 6-fold higher than for the susceptible biotype. The resistant biotype was also resistant to diquat, but was susceptible to glyphosate at 720 g and metribuzin at 300 g. Application of 100 g paraquat at anthesis completely suppressed seed set of the susceptible biotype and reduced that of the resistant biotype by 95%. Seed set by the paraquat-treated resistant biotype, however, showed little reduction. This is the 4th species to have been found to be resistant to bipyridyl herbicides in this field; the other herbicide resistant weeds are Hordeum glaucum, H. leporinum [Hordeum murinum subsp. leporinum] and Arctotheca calendula..

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