International Survey of Herbicide-Resistant Weeds

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(Bidens pilosa)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Brazil, Mato Grosso Do Sul
Hairy Beggarticks (Bidens pilosa) is a dicot weed in the Asteraceae family.  In Brazil this weed first evolved resistance to Group 2 (Legacy B) herbicides in 1993 and infests 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, imazaquin, imazethapyr, nicosulfuron, and pyrithiobac-sodium 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 Dec 07, 2000 )

Common NameHairy Beggarticks
SpeciesBidens pilosa
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicideschlorimuron-ethyl, imazaquin, imazethapyr, nicosulfuron, and pyrithiobac-sodium
LocationBrazil, Mato Grosso Do Sul
Contributors - (Alphabetically)Pedro Christoffoleti 
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Pedro Christoffoleti
The fist site of B. pilosa resistant to ALS inhibitor herbicide was found after 6 applications of imazaquin/chlorimuron in the soybean area. The areas with this weed occurs is a mixture of the species Bidens pilosa and Bidens subalternans. Bioassays and dose response curves has been conducted in the greenhouse conditions as ESALQ/USP - Brazil in Master of Science Dissertation by Patricia A. Monqueiro, adviser by Pedro J. Christoffoleti, and it proved a cross resistance of this biotype to Sulfonilureia, Imidazolinone, Triazolopiirimidina and Pirimidiloxibenzoato. Also some laboratory test has proved that resistance is due to an altered site of the ALS enzyme. The summary of Patrícia's dissertation is as follow: The weeds Bidens pilosa/Bidens subalternans and Amaranthus quitensis are controlled in the soybean crop by herbicides; but the acetolactate synthase (ALS - code EC inhibitor herbicides are the most sprayed by soybean growers. However, the intensive and repetitive use of these herbicides in São Gabriel do Oeste county (MS - Brazil) and in the provinces of Córdoba and Tucumã (Argentina), selected resistant biotypes of these weeds. Therefore, it was developed a research project aiming to study the biology, management and the genetic/biochemical caracterization, using these weed biotypes. From greenhouse experiments dose-response curves and GR50 values were obtained, proving the cross resistance to imidazolinones and sulfonylureas of Bidens pilosa/Bidens subalternans and Amaranthus quitensis. It was also evaluated, under field conditons, the control of the resistant biotype of Bidens pilosa/Bidens subalternans to ALS inhibitor herbicides and alternatives (herbicides with different mechanism of action from ALS inhibition). It was concluded that the herbicide chlorimuron-ethyl and imazethapyr, at reccommended rate did not control the resistant biotype, but the alternative herbicides lactofen, fomesafen and bentazon were efficient. Seeds of Bidens pilosa/Bidens subalternans from plants of the ALS inhibitor herbicides failure in the field experiment and Amaranthus quitensis scapes from Argentina, were collected and used to install experiments in the greennhouse, whete it was tested the same treatements used in the field experiment. The results proved that alternative herbicides, sprayed alone, or in mixture with ALS inhibitor, controlled efficently both resistant and susceptible populations. It was conducted experiments of growth analysis of the resistant and susceptible biotypes of these weeds, in order to compare the competitive ability of the biotypes. According to the results, there is no adaptative cost to the resistant biotype. It was conducted a bioassay, in order to test a rapid detection of resistant biotypes to ALS inhibitor herbicides, spraying at the same time inhibitor herbicides of ALS and KARI (an enzyme that act in the reaction right after the acetolactate formation). The results of the acetolactate accumulation in resistant plants was meassured by the accumulation of acetoin, which concentration was meassured by the color of the solution developed in naphtol and creatine. By this test it was possible to confirm the resistance of the biotypes of Bidens pilosa/Bidens subalternans and Amaranthus quitensis due to an insensitivity of the ALS. The sequencing of the gen that codify the ALS in resistant and susceptible of Amaranthus quitensis, did not show any mutation in the Domain A, suggesting that other possition

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Confirmation Tests

Field, Greenhouse, and Laboratory trials comparing a known susceptible Hairy Beggarticks biotype with this Hairy Beggarticks 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 Hairy Beggarticks indicate that the inheritance is determined by a nuclear trait.  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 2 (Legacy B) resistant Hairy Beggarticks from Brazil 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 2 (Legacy B) resistant Hairy Beggarticks from Brazil please update the database.
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Associate Professor III
Universidade de Sao Paulo
Crop Science Department
ESALQ - USP - LPV - Av. Padua Dias 11 - C. Postal 09
Piracicaba, 13418-900, São Paulo
Email Pedro Christoffoleti
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Brazil have been instrumental in providing you this information. Particular thanks is given to Pedro Christoffoleti for providing detailed information.
Herbicide Resistant Hairy Beggarticks Globally
(Bidens pilosa)
Herbicide Resistant Hairy Beggarticks Globally
(Bidens pilosa)
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Herbicide Resistant Hairy Beggarticks Globally
(Bidens pilosa)
#CountryFirstYearSituationActive IngredientsSite of Action
1 BrazilBrazil 1993 Soybean chlorimuron-ethyl, imazaquin, imazethapyr, nicosulfuron, and pyrithiobac-sodium 5 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
32Bidens pilosaHairy Beggarticks42
2 BrazilBrazil 2016 Corn (maize), and Soybean atrazine, and imazethapyr 5 Multiple Resistance: 2 Sites of Action
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
32Bidens pilosaHairy Beggarticks14053
3 BrazilBrazil 2022 Soybean fomesafen 5 Inhibition of Protoporphyrinogen Oxidase ( HRAC Group 14 (Legacy E)
32Bidens pilosaHairy Beggarticks27288
4 KenyaKenya 1991 Coffee paraquat 26 PS I Electron Diversion ( HRAC Group 22 (Legacy D)
32Bidens pilosaHairy Beggarticks381
5 MexicoMexico 2014 Lime, and sour glyphosate 29 Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)
32Bidens pilosaHairy Beggarticks9923
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