Herbicide Resistant Weed Maps


  • Ontario repository of herbicide resistant weeds
  • Testing services for suspected herbicide resistant weeds
  • Ontario counties with confirmed herbicide resistant weed populations
  • Testing services for suspected herbicide resistant weeds
  • Ontario expertise in herbicide resistance

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    An online repository of all herbicide resistant weed testing results since 1998 can be found here. Users will be able to search for herbicide resistant weed species and create distribution maps.

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    There are two testing solutions available in Ontario. The plant bio-assay service offered by the Tardif lab at the University of Guelph requires that mature seed is collected in the fall and submitted. Plants are then grown from that seed and sprayed at various doses of the herbicide(s) suspected. Results are provided typically by March, the service is provided at no cost to Ontario farmers. The molecular testing service, requires plant tissue that is roughly “quarter sized”, so a single leaf is often adequate. Results can be obtained within a couple of weeks, but it is a fee based service. Fortunately, there is a funded surveillance project that will process samples at no cost. A sampling protocol for this project can be downloaded here.

  • Free plant bioassay testing by the University of Guelph
  • Molecular testing by TurnKey Genomics (private lab)

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    In Ontario there are 22 different weed species that are resistant to one or more herbicide groups. The table below contains all records of confirmed herbicide resistant weed species in Ontario since 1981 (as of February, 2021)

    Weed species confirmed resistant to a herbicide group by county in Ontario since 1981

    CountyWeed SpeciesHerbicide Group Example Herbicide(s)
    BrantLamb's-quarterGroup 5Aatrex, Sencor
    BrantGreen pigweedGroup 5Aatrex, Sencor
    BrantGoosefootGroup 5Aatrex, Sencor
    BrantCommon ragweedGroup 5Aatrex, Sencor
    BrantCanada fleabaneGroup 9glyphosate
    BrantCanada fleabaneGroup 2Classic, FirstRate
    BruceWaterhempGroup 2Pursuit, Pinnacle
    BruceRedroot pigweedGroup 2Pursuit, Classic
    BruceLamb's-quarterGroup 5Aatrex, Sencor
    BruceGreen pigweedGroup 2Pursuit, Classic
    BruceGreen pigweedGroup 5Aatrex, Sencor
    BruceEastern black nightshadeGroup 2Pursuit
    BruceCommon ragweedGroup 2Pursuit, Classic
    BruceCommon ragweedGroup 5Aatrex, Sencor
    BruceCanada fleabaneGroup 9glyphosate
    CarletonEastern black nightshadeGroup 2Pursuit
    CarletonCommon ragweedGroup 2Pursuit, Classic
    Chatham-KentWaterhempGroup 9glyphosate
    Chatham-KentRedroot pigweedGroup 2Pursuit, Classic
    Chatham-KentRedroot pigweedGroup 5Aatrex, Sencor
    Chatham-KentRedroot pigweedGroup 6Basagran, Pardner
    Chatham-KentRedroot pigweedGroup 7Lorox
    Chatham-KentLarge crabgrassGroup 1Assure II
    Chatham-KentLamb's-quarterGroup 2Pursuit, Pinnacle
    Chatham-KentLamb's-quarterGroup 5Aatrex, Sencor
    Chatham-KentGreen pigweedGroup 2Pursuit, Classic
    Chatham-KentGreen pigweedGroup 6Basagran, Pardner
    Chatham-KentGreen pigweedGroup 5Aatrex, Sencor
    Chatham-KentGiant RagweedGroup 9glyphosate
    Chatham-KentGiant RagweedGroup 2Pursuit, Classic
    Chatham-KentEastern black nightshadeGroup 22Reglone, Gramoxone
    Chatham-KentCommon ragweedGroup 2Pursuit, Classic
    Chatham-KentCanada fleabaneGroup 9glyphosate
    Chatham-KentCanada fleabaneGroup 2Classic, FirstRate
    DufferinLamb's-quarterGroup 5Aatrex, Sencor
    DufferinGreen pigweedGroup 5Aatrex, Sencor
    DufferinCanada fleabaneGroup 9glyphosate
    DurhamLamb's-quarterGroup 5Aatrex, Sencor
    DurhamGreen pigweedGroup 5Aatrex, Sencor
    DurhamCanada fleabaneGroup 9glyphosate
    ElginRedroot pigweedGroup 2Pursuit, Classic
    ElginLamb's-quarterGroup 2Pursuit, Pinnacle
    ElginLamb's-quarterGroup 5Aatrex, Sencor
    ElginGreen pigweedGroup 2Pursuit, Classic
    ElginGreen pigweedGroup 5Aatrex, Sencor
    ElginGreen pigweedGroup 5Aatrex, Sencor
    ElginGiant foxtailGroup 2Accent, Pursuit
    ElginEastern black nightshadeGroup 2Pursuit
    ElginCommon ragweedGroup 2Pursuit, Classic
    ElginCanada fleabaneGroup 9glyphosate
    ElginCanada fleabaneGroup 2Classic, FirstRate
    EssexWaterhempGroup 5Aatrex, Sencor
    EssexWaterhempGroup 9glyphosate
    EssexWaterhempGroup 2Classic, Pinnacle, Pursuit
    EssexWaterhempGroup 14Reflex, Blazer
    EssexSmooth pigweedGroup 6Basagran, Pardner
    EssexRedroot pigweedGroup 2Pursuit, Classic
    EssexRedroot pigweedGroup 6Basagran, Pardner
    EssexLamb's-quarterGroup 2Pursuit, Pinnacle
    EssexLamb's-quarterGroup 5Aatrex, Sencor
    EssexGreen pigweedGroup 2Pursuit, Classic
    EssexGreen pigweedGroup 6Basagran, Pardner
    EssexGreen pigweedGroup 5Aatrex, Sencor
    EssexGiant RagweedGroup 9glyphosate
    EssexGiant RagweedGroup 2Pursuit, Classic
    EssexGiant foxtailGroup 2Accent, Pursuit
    EssexField peppergrassGroup 22Reglone, Gramoxone
    EssexCommon ragweedGroup 2Pursuit, Classic
    EssexCommon ragweedGroup 9glyphosate
    EssexCommon ragweedGroup 5Aatrex, Sencor
    EssexCanada fleabaneGroup 22Reglone, Gramoxone
    EssexCanada fleabaneGroup 2Classic, FirstRate
    FrontenacLamb's-quarterGroup 5Aatrex, Sencor
    FrontenacGreen pigweedGroup 5Aatrex, Sencor
    FrontenacCanada fleabaneGroup 9glyphosate
    FrontenacCanada fleabaneGroup 2Classic, FirstRate
    GreyWitchgrassGroup 5Aatrex, Sencor
    GreyLamb's-quarterGroup 5Aatrex, Sencor
    GreyGreen pigweedGroup 5Aatrex, Sencor
    HaldimandWitchgrassGroup 5Aatrex, Sencor
    HaldimandRedroot pigweedGroup 2Pursuit, Classic
    HaldimandLamb's-quarterGroup 5Aatrex, Sencor
    HaldimandGreen pigweedGroup 2Pursuit, Classic
    HaldimandGreen pigweedGroup 5Aatrex, Sencor
    HaldimandCommon ragweedGroup 2Pursuit, Classic
    HaldimandCommon ragweedGroup 5Aatrex, Sencor
    HaldimandCanada fleabaneGroup 9glyphosate
    HaldimandCanada fleabaneGroup 2Classic, FirstRate
    HaliburtonLamb's-quarterGroup 5Aatrex, Sencor
    HaliburtonGreen pigweedGroup 5Aatrex, Sencor
    HaltonWild CarrotGroup 4dicamba, 2,4-D
    HaltonLamb's-quarterGroup 5Aatrex, Sencor
    HaltonGreen pigweedGroup 5Aatrex, Sencor
    HaltonCanada fleabaneGroup 9glyphosate
    HaltonCanada fleabaneGroup 2Classic, FirstRate
    HamiltonRedroot pigweedGroup 2Pursuit, Classic
    HamiltonLamb's-quarterGroup 5Aatrex, Sencor
    HamiltonGreen pigweedGroup 2Pursuit, Classic
    HamiltonGreen pigweedGroup 5Aatrex, Sencor
    HamiltonCommon ragweedGroup 5Aatrex, Sencor
    HamiltonCanada fleabaneGroup 9glyphosate
    HamiltonCanada fleabaneGroup 2Classic, FirstRate
    HastingsLamb's-quarterGroup 5Aatrex, Sencor
    HastingsCanada fleabaneGroup 9glyphosate
    HuronRedroot pigweedGroup 2Pursuit, Classic
    HuronRedroot pigweedGroup 7Lorox
    HuronLamb's-quarterGroup 5Aatrex, Sencor
    HuronGreen pigweedGroup 2Pursuit, Classic
    HuronGreen pigweedGroup 5Aatrex, Sencor
    HuronGreen pigweedGroup 5Aatrex, Sencor
    HuronGreen foxtailGroup 2Accent, Pursuit
    HuronEastern black nightshadeGroup 2Pursuit
    HuronCommon ragweedGroup 2Pursuit, Classic
    HuronCanada fleabaneGroup 9glyphosate
    HuronCanada fleabaneGroup 2Classic, FirstRate
    Kawartha LakesLamb's-quarterGroup 5Aatrex, Sencor
    Kawartha LakesGreen pigweedGroup 5Aatrex, Sencor
    Kawartha LakesGreen foxtailGroup 2Accent, Pursuit
    LambtonWaterhempGroup 5Aatrex, Sencor
    LambtonWaterhempGroup 9glyphosate
    LambtonWaterhempGroup 2Classic, Pinnacle, Pursuit
    LambtonWaterhempGroup 14Reflex, Blazer
    LambtonRedroot pigweedGroup 2Pursuit, Classic
    LambtonLamb's-quarterGroup 2Pursuit, Pinnacle
    LambtonLamb's-quarterGroup 5Aatrex, Sencor
    LambtonGreen pigweedGroup 2Pursuit, Classic
    LambtonGreen pigweedGroup 5Aatrex, Sencor
    LambtonGreen foxtailGroup 2Accent, Pursuit
    LambtonGiant RagweedGroup 9glyphosate
    LambtonGiant RagweedGroup 2Pursuit, Classic
    LambtonGiant foxtailGroup 2Accent, Pursuit
    LambtonCommon ragweedGroup 2Pursuit, Classic
    LambtonCockleburGroup 2Pursuit, Classic
    LambtonCanada fleabaneGroup 9glyphosate
    LambtonCanada fleabaneGroup 2Classic, FirstRate
    LanarkLamb's-quarterGroup 5Aatrex, Sencor
    LanarkGreen pigweedGroup 5Aatrex, Sencor
    Leeds and GrenvilleWitchgrassGroup 5Aatrex, Sencor
    Leeds and GrenvilleLamb's-quarterGroup 5Aatrex, Sencor
    Leeds and GrenvilleGreen pigweedGroup 5Aatrex, Sencor
    Lennox and AddingtonRedroot pigweedGroup 2Pursuit, Classic
    Lennox and AddingtonLamb's-quarterGroup 5Aatrex, Sencor
    Lennox and AddingtonGreen pigweedGroup 2Pursuit, Classic
    Lennox and AddingtonGreen pigweedGroup 5Aatrex, Sencor
    Lennox and AddingtonGiant RagweedGroup 9glyphosate
    Lennox and AddingtonCommon ragweedGroup 5Aatrex, Sencor
    Lennox and AddingtonCanada fleabaneGroup 9glyphosate
    Lennox and AddingtonCanada fleabaneGroup 2Classic, FirstRate
    MiddlesexRedroot pigweedGroup 2Pursuit, Classic
    MiddlesexRedroot pigweedGroup 7Lorox
    MiddlesexLamb's-quarterGroup 2Pursuit, Pinnacle
    MiddlesexLamb's-quarterGroup 5Aatrex, Sencor
    MiddlesexGreen pigweedGroup 2Pursuit, Classic
    MiddlesexGreen pigweedGroup 7Lorox
    MiddlesexGreen pigweedGroup 7Linuron
    MiddlesexGreen pigweedGroup 5Aatrex, Sencor
    MiddlesexEastern black nightshadeGroup 2Pursuit
    MiddlesexCommon ragweedGroup 2Pursuit, Classic
    MiddlesexCanada fleabaneGroup 9glyphosate
    NiagaraLamb's-quarterGroup 5Aatrex, Sencor
    NiagaraGreen pigweedGroup 5Aatrex, Sencor
    NiagaraGreen pigweedGroup 5Aatrex, Sencor
    NiagaraCommon ragweedGroup 2Pursuit, Classic
    NiagaraCommon ragweedGroup 5Aatrex, Sencor
    NiagaraCanada fleabaneGroup 9glyphosate
    NiagaraCanada fleabaneGroup 2Classic, FirstRate
    NorfolkWitchgrassGroup 5Aatrex, Sencor
    NorfolkLamb's-quarterGroup 5Aatrex, Sencor
    NorfolkCommon ragweedGroup 5Aatrex, Sencor
    NorfolkCommon ragweedGroup 5Aatrex, Sencor
    NorfolkCommon ragweedGroup 2Pursuit, Classic
    NorfolkCanada fleabaneGroup 9glyphosate
    NorfolkCanada fleabaneGroup 2Classic, FirstRate
    NorthumberlandLamb's-quarterGroup 5Aatrex, Sencor
    NorthumberlandGreen pigweedGroup 5Aatrex, Sencor
    NorthumberlandCanada fleabaneGroup 9glyphosate
    NorthumberlandCanada fleabaneGroup 2Classic, FirstRate
    OttawaLamb's-quarterGroup 5Aatrex, Sencor
    OttawaGreen pigweedGroup 5Aatrex, Sencor
    OttawaEastern black nightshadeGroup 2Pursuit
    OttawaCommon ragweedGroup 2Pursuit, Classic
    OttawaCanada fleabaneGroup 9glyphosate
    OxfordRedroot pigweedGroup 2Pursuit, Classic
    OxfordLamb's-quarterGroup 5Aatrex, Sencor
    OxfordGreen pigweedGroup 2Pursuit, Classic
    OxfordGreen pigweedGroup 5Aatrex, Sencor
    OxfordGreen pigweedGroup 5Aatrex, Sencor
    OxfordGreen foxtailGroup 2Accent, Pursuit
    OxfordGiant foxtailGroup 2Accent, Pursuit
    OxfordEastern black nightshadeGroup 2Pursuit
    OxfordCommon ragweedGroup 2Pursuit, Classic
    OxfordCanada fleabaneGroup 9glyphosate
    OxfordCanada fleabaneGroup 2Classic, FirstRate
    PeelLamb's-quarterGroup 5Aatrex, Sencor
    PeelGreen pigweedGroup 5Aatrex, Sencor
    PeelCanada fleabaneGroup 9glyphosate
    PeelCanada fleabaneGroup 2Classic, FirstRate
    PerthRedroot pigweedGroup 2Pursuit, Classic
    PerthLamb's-quarterGroup 5Aatrex, Sencor
    PerthGreen pigweedGroup 2Pursuit, Classic
    PerthGreen foxtailGroup 2Accent, Pursuit
    PerthEastern black nightshadeGroup 2Pursuit
    PerthCommon ragweedGroup 2Pursuit, Classic
    PerthCanada fleabaneGroup 9glyphosate
    PerthCanada fleabaneGroup 2Classic, FirstRate
    PeterboroughLamb's-quarterGroup 5Aatrex, Sencor
    PeterboroughGreen pigweedGroup 5Aatrex, Sencor
    PeterboroughCanada fleabaneGroup 9glyphosate
    PeterboroughCanada fleabaneGroup 2Classic, FirstRate
    Prescott-RussellWitchgrassGroup 5Aatrex, Sencor
    Prescott-RussellLamb's-quarterGroup 5Aatrex, Sencor
    Prescott-RussellGreen pigweedGroup 5Aatrex, Sencor
    Prescott-RussellCommon ragweedGroup 2Pursuit, Classic
    Prince EdwardLamb's-quarterGroup 5Aatrex, Sencor
    Prince EdwardCanada fleabaneGroup 9glyphosate
    RenfrewLamb's-quarterGroup 5Aatrex, Sencor
    SimcoeRedroot pigweedGroup 2Pursuit, Classic
    SimcoeRedroot pigweedGroup 5Aatrex, Sencor
    SimcoeRedroot pigweedGroup 7Lorox
    SimcoeLamb's-quarterGroup 2Pursuit, Pinnacle
    SimcoeLamb's-quarterGroup 5Aatrex, Sencor
    SimcoeGreen pigweedGroup 2Pursuit, Classic
    SimcoeGreen pigweedGroup 5Aatrex, Sencor
    SimcoeGreen pigweedGroup 7Lorox
    SimcoeGreen pigweedGroup 7Linuron
    SimcoeEastern black nightshadeGroup 2Pursuit
    SimcoeCommon ragweedGroup 2Pursuit, Classic
    SimcoeCanada fleabaneGroup 9glyphosate
    Stormont, Dundas & GlengarryWild mustardGroup 5Aatrex, Sencor
    Stormont, Dundas & GlengarryRedroot pigweedGroup 2Pursuit, Classic
    Stormont, Dundas & GlengarryRedroot pigweedGroup 5Aatrex, Sencor
    Stormont, Dundas & GlengarryLamb's-quarterGroup 2Pursuit, Pinnacle
    Stormont, Dundas & GlengarryLamb's-quarterGroup 5Aatrex, Sencor
    Stormont, Dundas & GlengarryGreen pigweedGroup 2Pursuit, Classic
    Stormont, Dundas & GlengarryGreen pigweedGroup 5Aatrex, Sencor
    Stormont, Dundas & GlengarryEastern black nightshadeGroup 2Pursuit
    Stormont, Dundas & GlengarryCommon ragweedGroup 2Pursuit, Classic
    Stormont, Dundas & GlengarryCanada fleabaneGroup 9glyphosate
    Stormont, Dundas & GlengarryCanada fleabaneGroup 2Classic, FirstRate
    VictoriaGreen foxtailGroup 2Accent, Pursuit
    WaterlooRedroot pigweedGroup 5Aatrex, Sencor
    WaterlooLamb's-quarterGroup 5Aatrex, Sencor
    WaterlooGreen pigweedGroup 5Aatrex, Sencor
    WaterlooCanada fleabaneGroup 9glyphosate
    WaterlooCanada fleabaneGroup 2Classic, FirstRate
    WaterlooBarnyardgrassGroup 5Aatrex, Sencor
    WellingtonWitchgrassGroup 5Aatrex, Sencor
    WellingtonRedroot pigweedGroup 2Pursuit, Classic
    WellingtonLamb's-quarterGroup 5Aatrex, Sencor
    WellingtonGreen pigweedGroup 2Pursuit, Classic
    WellingtonGreen pigweedGroup 5Aatrex, Sencor
    WellingtonGreen foxtailGroup 2Accent, Pursuit
    WellingtonEastern black nightshadeGroup 2Pursuit
    WellingtonCommon ragweedGroup 2Pursuit, Classic
    WellingtonCommon ragweedGroup 5Aatrex, Sencor
    WellingtonCanada fleabaneGroup 9glyphosate
    WellingtonCanada fleabaneGroup 2Classic, FirstRate
    YorkYellow foxtailGroup 5Aatrex, Sencor
    YorkLamb's-quarterGroup 5Aatrex, Sencor
    YorkGreen pigweedGroup 5Aatrex, Sencor
    YorkCommon groundselGroup 5Aatrex, Sencor
    YorkCanada fleabaneGroup 9glyphosate
    YorkCanada fleabaneGroup 2Classic, FirstRate
    Chatham-KentWaterhempGroup 2Pursuit, Pinnacle, Classic
    Chatham-KentWaterhempGroup 5Aatrex, Sencor
    Chatham-KentWaterhempGroup 14Reflex, Blazer
    HuronWaterhempGroup 2Pursuit, Pinnacle, Classic
    HuronWaterhempGroup 5Aatrex, Sencor
    HuronWaterhempGroup 9glyphosate
    HuronWaterhempGroup 14Reflex, Blazer
    HaldimandWaterhempGroup 2Pursuit, Pinnacle, Classic
    HaldimandWaterhempGroup 5Aatrex, Sencor
    HaldimandWaterhempGroup 9glyphosate
    HaldimandWaterhempGroup 14Reflex, Blazer
    MiddlesexWaterhempGroup 2Pursuit, Pinnacle, Classic
    MiddlesexWaterhempGroup 5Aatrex, Sencor
    MiddlesexWaterhempGroup 9glyphosate
    NorfolkWaterhempGroup 2Pursuit, Pinnacle, Classic
    NorfolkWaterhempGroup 9glyphosate
    NorfolkWaterhempGroup 14Reflex, Blazer
    WellingtonWaterhempGroup 2Pursuit, Pinnacle, Classic
    WellingtonWaterhempGroup 9glyphosate
    WellingtonWaterhempGroup 14Reflex, Blazer
    BrantWaterhempGroup 2Pursuit, Pinnacle, Classic
    BrantWaterhempGroup 9glyphosate
    BruceWaterhempGroup 9glyphosate
    ElginWaterhempGroup 2Pursuit, Pinnacle, Classic
    ElginWaterhempGroup 9glyphosate
    NorthumberlandWaterhempGroup 2Pursuit, Pinnacle, Classic
    NorthumberlandWaterhempGroup 9glyphosate
    WentworthWaterhempGroup 2Pursuit, Pinnacle, Classic
    WentworthWaterhempGroup 9glyphosate
    EssexCanada fleabaneGroup 9glyphosate
    WellingtonWild CarrotGroup 4dicamba, 2,4-D
    HuronLarge crabgrassGroup 1Assure II
    Last updated Feb 2021

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Academia (in alphabetical order):
Dr. François Tardif, University of Guelph (Main campus)
Dr. Peter Sikkema, University of Guelph (Ridgetown campus)

Extension (in alphabetical order):
Mike Cowbrough, OMAFRA Weed Specialist (Field Crops)
Kristen Obeid, OMAFRA Weed Specialist (Horticulture Crops)