(Ammannia auriculata)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Eared Redstem (Ammannia auriculata) is a dicot weed in the Lythraceae family.  In China this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2023 and infests Rice.   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 bensulfuron-methyl 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.

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QUIK STATS (last updated Mar 11, 2023 )

Common NameEared Redstem
SpeciesAmmannia auriculata
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Contributors - (Alphabetically)Ian Heap 
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Competitiveness of bensulfuron-methyl-susceptible and -resistant biotypes of Ammannia auriculata Willd. in direct-seeded rice.

Author(s) : Yang SiYu ;  Liu Jie ;  Liu Rui ;  Zhou GuoJun ;  Chen Chang ;  Zhou WeiJun ;  Basharat Ali ;  Gui WenJun ;  Zhu JinWen ;  Ditommaso, A.

Author Affiliation : Ministry of Agriculture and Rural Affairs Key Lab of Molecular Biology of Crop Pathogens and Insects, Department of Plant Protection, Zhejiang University, Hangzhou 310058, China.

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 Journal article : Agronomy 2023 Vol.13 No.4

Abstract : Ammannia auriculata Willd. (eared redstem) has become one of the most troublesome weeds in paddy rice in China. Resistance to bensulfuron-methyl (BSM) has spread extensively in this species. Greenhouse and field experiments were conducted to determine how the eared redstem biotype and density affect competition against rice. In the greenhouse experiment, five treatments were tested: a BSM-susceptible biotype at low density (58 plants m-2, SL), a BSM-susceptible biotype at high density (288 plants m-2, SH), a BSM-resistant biotype at low density (RL), a BSM-resistant biotype at high density (RH), and a control without eared redstem (CK). Eared redstem grew slowly until 15 days after sowing (DAS); however, growth accelerated after 20 DAS, and the eared redstem plants were taller than the rice from 55 DAS on. The SH and RH treatments were associated with greater intraspecific competition: eared redstem plants in the SH and RH treatments had fewer branches, fewer capsules, and less shoot dry weight per individual plant relative to the SL and RL treatments. The SH and RH treatments also caused greater reductions in the rice yield. The dry weight of rice at 141 DAS was reduced by 73% in the SL treatment, 98% in the SH treatment, 51% in the RL treatment, and 82% in the RH treatment, all relative to the CK. At 141 DAS, BSM-resistant plants were smaller than BSM-susceptible plants, suggesting a fitness cost of herbicide resistance in the absence of a herbicide. In the field study, eared redstem densities as low as 5 plants m-2 reduced the rice yield by 22%. A density of 50 eared redstem plants m-2 reduced the rice yield by 70%. Overall, these findings demonstrate that eared redstem is a highly aggressive weed species and threatens the rice yield even at a low density. However, the findings also demonstrate that BSM-resistant populations are less competitive. There is an urgent need to develop integrated management programs for this aggressive weed, which may include tactics to shift competitive dynamics in favor of rice. Additionally, this research provides the theoretical basis for the damage level, resistance risk evaluation, and management strategy of eared redstem in rice cropping systems.

ISSN : 2073-4395

DOI : 10.3390/agronomy13041152  

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Confirmation Tests

Field, and Greenhouse trials comparing a known susceptible Eared Redstem biotype with this Eared Redstem 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 HRAC Group 2 resistant Eared Redstem 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 Eared Redstem from China please update the database.
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International Survey of Herbicide-Resistant Weeds
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The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in China have been instrumental in providing you this information. Particular thanks is given to Ian Heap for providing detailed information.
Herbicide Resistant Eared Redstem Globally
(Ammannia auriculata)
Herbicide Resistant Eared Redstem Globally
(Ammannia auriculata)
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Herbicide Resistant Eared Redstem Globally
(Ammannia auriculata)
#CountryFirstYearSituationActive IngredientsSite of Action
1 ChinaChina 2023 Rice bensulfuron-methyl 9 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
183Ammannia auriculataEared Redstem27280
2 United States (California) United StatesCalifornia1997 Rice bensulfuron-methyl 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
183Ammannia auriculataEared Redstem1098
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Heap, I.  The International Herbicide-Resistant Weed Database.  Online.  Thursday, July 18, 2024 .  Available Copyright © 1993- 2024 All rights reserved. Fair use of this material is encouraged. Proper citation is requested.