International Survey of Herbicide-Resistant Weeds

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Status of Herbicide Resistance in Idaho - Donn Thill : January, 2014

In north Idaho, the serious herbicide resistant weed is Italian ryegrass. There are biotypes resistant to all group 1 herbicides, most group 2 and flufenacet (15). Other biotypes have a mixed bag of resistance; resistance to several group ones, but not cethodim or pinoxadim. Nearly 75% of ryegrass infestation are resistant to the older group 1 herbicides – those listed in the table. Group 2 resistance is becoming more common. We are relying group 15; flufenacet and pyroxosulfone (to be registered soon). So far there is no cross resistance reported to the two group 15 herbicides. In southern Idaho, the most serious herbicide resistant weed is likely kochia.
Herbicide Resistant Weeds in Idaho, United States.
#YearSpeciesSite of ActionActivesContacts
1 230Prickly Lettuce1987Lactuca serriola
Prickly Lettuce		United States
(Idaho)		Idaho  Inhibition of Acetolactate Synthase (B/2) Inhibition of Acetolactate Synthase (B/2) chlorsulfuron, imazethapyr, metsulfuron-methyl, thifensulfuron-methyl, triasulfuron, tribenuron-methyl Donn Thill
2 232Kochia1989Kochia scoparia
Kochia		United States
(Idaho)		IdahoID Inhibition of Acetolactate Synthase (B/2) Inhibition of Acetolactate Synthase (B/2) chlorsulfuron Donn Thill
3 512Russian-thistle1990Salsola tragus
Russian-thistle		United States
(Idaho)		IdahoID Inhibition of Acetolactate Synthase (B/2) Inhibition of Acetolactate Synthase (B/2) chlorsulfuron Donn Thill
4 519Italian Ryegrass1991Lolium perenne ssp. multiflorum
Italian Ryegrass		United States
(Idaho)		Idaho  Inhibition of Acetyl CoA Carboxylase (A/1) Inhibition of Acetyl CoA Carboxylase (A/1) clodinafop-propargyl, diclofop-methyl, quizalofop-ethyl, sethoxydim Steven Seefeldt, Donn Thill
5 235Wild Oat1992Avena fatua
Wild Oat		United States
(Idaho)		IdahoID Inhibition of Acetyl CoA Carboxylase (A/1) Inhibition of Acetyl CoA Carboxylase (A/1) clodinafop-propargyl, diclofop-methyl, fenoxaprop-ethyl Donn Thill
6 234Wild Oat1993Avena fatua
Wild Oat		United States
(Idaho)		IdahoID Cell elongation inhibitors (Z/8), Very Long-Chain Fatty Acid Synthesis inhibitors (K3 N/15) Multiple Resistance: 2 Sites of Action
Cell elongation inhibitors (Z/8)
Very Long-Chain Fatty Acid Synthesis inhibitors (K3 N/15) 		difenzoquat, tri-allate Donn Thill
7 524Mayweed Chamomile1997Anthemis cotula
Mayweed Chamomile		United States
(Idaho)		Idaho  Inhibition of Acetolactate Synthase (B/2) Inhibition of Acetolactate Synthase (B/2) chlorsulfuron, imazethapyr, thifensulfuron-methyl, tribenuron-methyl Steven Seefeldt, Donn Thill
8 1058Kochia1997Kochia scoparia
Kochia		United States
(Idaho)		IdahoID Auxin Mimics (O/4) Auxin Mimics (O/4) dicamba Don Morishita
9 5280Italian Ryegrass2005Lolium perenne ssp. multiflorum
Italian Ryegrass		United States
(Idaho)		Idaho  Inhibition of Acetolactate Synthase (B/2), Inhibition of Acetyl CoA Carboxylase (A/1), Very Long-Chain Fatty Acid Synthesis inhibitors (K3 N/15) Multiple Resistance: 3 Sites of Action
Inhibition of Acetolactate Synthase (B/2)
Inhibition of Acetyl CoA Carboxylase (A/1)
Very Long-Chain Fatty Acid Synthesis inhibitors (K3 N/15) 		clethodim, clodinafop-propargyl, diclofop-methyl, flufenacet, quizalofop-ethyl, triasulfuron Donn Thill
10 5293Redroot Pigweed2005Amaranthus retroflexus
Redroot Pigweed		United States
(Idaho)		Idaho  PSII inhibitors - Serine 264 Binders (C1 C2/5) PSII inhibitors - Serine 264 Binders (C1 C2/5) metribuzin Pamela Hutchinson
11 9945Kochia2014Kochia scoparia
Kochia		United States
(Idaho)		Idaho  Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9) Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9) glyphosate Don Morishita, Prashant Jha
12 27264Tall Waterhemp2023Amaranthus tuberculatus (=A. rudis)
Tall Waterhemp		United States
(Idaho)		Idaho  Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9) Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9) glyphosate Todd Gaines, Joel Felix, Lucas Araújo, Albert Adjesiwor, Clarke Alder
13 27265Palmer Amaranth2023Amaranthus palmeri
Palmer Amaranth		United States
(Idaho)		Idaho  Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9) Inhibition of Enolpyruvyl Shikimate Phosphate Synthase (G/9) glyphosate Todd Gaines, Joel Felix, Lucas Araújo, Albert Adjesiwor, Clarke Alder
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Cite this site as: Heap, I.  The International Survey of Herbicide Resistant Weeds.  Online.  Internet.  Tuesday, July 1, 2025 .  Available  www.weedscience.org
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