International Survey of Herbicide-Resistant Weeds

Countries Weeds Herbicides Mutations Graphs References Researchers
(Anthemis cotula)

ALS inhibitors (B/2)

United States, Washington
Mayweed Chamomile (Anthemis cotula) is a dicot weed in the Asteraceae family.  In Washington this weed first evolved resistance to Group B/2 herbicides in 2010 and infests Spring Barley, and Wheat.   Group B/2 herbicides are known as ALS inhibitors (Inhibition of acetolactate synthase ALS (acetohydroxyacid synthase AHAS)).  Research has shown that these particular biotypes are resistant to cloransulam-methyl, imazethapyr, thifensulfuron-methyl, and tribenuron-methyl and they may be cross-resistant to other Group B/2 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.

If we do not have a picture for this weed, or you can provide a better picture (scan, digital camera etc) please please e-mail it to us.

QUIK STATS (last updated Apr 15, 2015 )

Common NameMayweed Chamomile
SpeciesAnthemis cotula
GroupALS inhibitors (B/2)
Herbicidescloransulam-methyl, imazethapyr, thifensulfuron-methyl, and tribenuron-methyl
LocationUnited States, Washington
Situation(s)Spring Barley, and Wheat
Contributors - (Alphabetically)Carol Mallory-Smith, and Alejandro Perez-Jones 
Edit this Case  |  Add New Case of Resistance  |  Add Note



Carol Mallory-Smith

Multiple Pro197 ALS Substitutions Endow Resistance to ALS Inhibitors within and among Mayweed Chamomile Populations. 2011. Suphannika Intanon, Alejandro Perez-Jones, Andrew G. Hulting, and Carol A. Mallory-Smith. Weed Science 2011 59:431–437 

Mayweed chamomile seeds were collected from six different fields across the Pacific Northwest. All populations (each collection site was considered a population) were suspected to have some level of acetolactate synthase (ALS) resistance. Greenhouse and laboratory studies were conducted to determine if these populations were resistant to three different classes of ALS inhibitors: sulfonylureas (SU), imidazolinones (IMI), and triazolopyrimidines (TP). A whole-plant dose–response and in vitro ALS activity studies confirmed cross-resistance to thifensulfuron + tribenuron/chlorsulfuron (SU), imazethapyr (IMI), and cloransulam (TP); however, resistance varied by herbicide class and population. Two ALS isoforms of the ALS gene (ALS1 and ALS2) were identified in mayweed chamomile; however, only mutations in ALS1 were responsible for resistance. No mutations were found in ALS2. Sequence analysis of the partial ALS gene identified four point mutations at position 197 (Pro197 to Leu, Gln, Thr, or Ser) in the resistant populations. This study demonstrates genotypic variation associated with cross-resistance to ALS inhibitors within and between populations.

Edit this Note  |  Add New Note


Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Mayweed Chamomile biotype with this Mayweed Chamomile 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 Group B/2 resistant Mayweed Chamomile 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 B/2 resistant Mayweed Chamomile from Washington 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 B/2 resistant Mayweed Chamomile from Washington please update the database.
Edit Case  |  Add Note  |  Add Article  |  Add New Case  |  Help


Oregon State University
Department of Crop And Soil Science
331B Crop Science Bldg
Corvallis, 97331, Oregon
United States
Email Carol Mallory-Smith
Web   : Web Site Link
Weed Research Specialist
Chemistry Technology
402 West State Farm Road
St. Louis, 63167, Missouri
United States
Email Alejandro Perez-Jones
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Washington have been instrumental in providing you this information. Particular thanks is given to Carol Mallory-Smith, and Alejandro Perez-Jones for providing detailed information.
Herbicide Resistant Mayweed Chamomile Globally
(Anthemis cotula)
Herbicide Resistant Mayweed Chamomile Globally
(Anthemis cotula)
Drag a column header and drop it here to group by that column
Herbicide Resistant Mayweed Chamomile Globally
(Anthemis cotula)
#CountryFirstYearSituationActive IngredientsSite of Action
1 ChileChile 2010 Wheat iodosulfuron-methyl-sodium, metsulfuron-methyl, and pyroxsulam 8 ALS inhibitors (B/2)
19Anthemis cotulaMayweed Chamomile5584
2 United States (Idaho) United StatesIdaho1997 Canola, Cereals, Chickpea, Lentils, Peas, and Wheat chlorsulfuron, imazethapyr, thifensulfuron-methyl, and tribenuron-methyl 45 ALS inhibitors (B/2)
19Anthemis cotulaMayweed Chamomile524
3 United States (Washington) United StatesWashington2010 Spring Barley, and Wheat cloransulam-methyl, imazethapyr, thifensulfuron-methyl, and tribenuron-methyl 45 ALS inhibitors (B/2)
19Anthemis cotulaMayweed Chamomile10987
Literature about Similar Cases

Page size:
Page: of 0
Items 0 to 0 of 0

Page size:
Page: of 0
Items 0 to 0 of 0
PERMISSION MUST BE OBTAINED FIRST if you intend to base a significant portion of a scientific paper on data derived from this site.
Cite this site as: Heap, I.  The International Survey of Herbicide Resistant Weeds.  Online.  Internet.  Sunday, September 20, 2020 .  Available
Copyright © 1993- 2020 All rights reserved. Fair use of this material is encouraged. Proper citation is requested.