Herbicide-Resistant Weeds in Cotton: Global Trends, Species Distribution and Herbicide Groups Affected
04 March 2026, Chicago: Herbicide resistance in weeds has become one of the most important agronomic challenges affecting cotton production worldwide. Over the past five decades, intensive herbicide use, particularly in cropping systems that rely heavily on chemical weed control, has created strong selection pressure on weed populations. As a result, several weed species have evolved resistance to herbicides that were once highly effective.
Cotton production systems are particularly vulnerable to herbicide resistance because of the widespread adoption of herbicide-tolerant varieties and the repeated use of similar herbicide modes of action. Herbicides such as glyphosate (EPSPS inhibitors), acetolactate synthase (ALS) inhibitors, and acetyl-CoA carboxylase (ACCase) inhibitors have been widely used in cotton systems for weed management. Over time, this repeated exposure has enabled certain weed species to develop resistance mechanisms that allow them to survive and reproduce despite herbicide applications.
Globally, herbicide-resistant weeds in cotton have been reported across several major cotton-producing regions including the United States, Brazil, Australia, China, Israel, Mexico, Paraguay, Greece and South Africa. Among these regions, the United States accounts for the largest number of documented cases, particularly in southern cotton-producing states such as Arkansas, Mississippi, Tennessee, Georgia and North Carolina.
One of the most problematic weeds globally is Palmer amaranth (Amaranthus palmeri). This species has evolved resistance to multiple herbicide groups including ALS inhibitors, glyphosate (EPSPS inhibitors), microtubule assembly inhibitors, protoporphyrinogen oxidase inhibitors and auxin mimics. In some cases, populations have developed resistance to five different herbicide sites of action, making management extremely difficult.
Other important resistant weeds in cotton include tall waterhemp (Amaranthus tuberculatus), horseweed (Conyza canadensis), goosegrass (Eleusine indica), johnsongrass (Sorghum halepense) and Italian ryegrass (Lolium perenne ssp. multiflorum). These species have developed resistance to different herbicide groups and are now widely reported in cotton fields across several countries.
Grass weeds such as junglerice (Echinochloa colona) and sourgrass (Digitaria insularis) have also evolved resistance to glyphosate in cotton production systems, particularly in Australia and South America. The emergence of multiple-resistant populations, capable of surviving herbicides from two or more groups, has further complicated weed management strategies.
| # | Year | Species | Common Name | Country / Region | Herbicide Site of Action |
|---|---|---|---|---|---|
| 1 | 1973 | Eleusine indica | Goosegrass | United States (North Carolina) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 2 | 1974 | Eleusine indica | Goosegrass | United States (South Carolina) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 3 | 1985 | Xanthium strumarium | Common Cocklebur | United States (South Carolina) | Nucleic acid inhibitors – HRAC Group 17 |
| 4 | 1987 | Eleusine indica | Goosegrass | United States (Alabama) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 5 | 1988 | Xanthium strumarium | Common Cocklebur | United States (Alabama) | Nucleic acid inhibitors – HRAC Group 17 |
| 6 | 1988 | Eleusine indica | Goosegrass | United States (Tennessee) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 7 | 1989 | Eleusine indica | Goosegrass | United States (Arkansas) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 8 | 1989 | Xanthium strumarium | Common Cocklebur | United States (Arkansas) | Nucleic acid inhibitors – HRAC Group 17 |
| 9 | 1989 | Amaranthus palmeri | Palmer Amaranth | United States (South Carolina) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 10 | 1991 | Sorghum halepense | Johnsongrass | United States (Mississippi) | ACCase inhibitors – HRAC Group 1 |
| 11 | 1991 | Xanthium strumarium | Common Cocklebur | United States (Tennessee) | Nucleic acid inhibitors – HRAC Group 17 |
| 12 | 1992 | Eleusine indica | Goosegrass | United States (Georgia) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 13 | 1992 | Xanthium strumarium | Common Cocklebur | United States (Louisiana) | Nucleic acid inhibitors – HRAC Group 17 |
| 14 | 1992 | Sorghum halepense | Johnsongrass | United States (Mississippi) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 15 | 1994 | Eleusine indica | Goosegrass | United States (Mississippi) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 16 | 1994 | Xanthium strumarium | Common Cocklebur | United States (Mississippi) | Nucleic acid inhibitors – HRAC Group 17 |
| 17 | 1994 | Amaranthus tuberculatus | Tall Waterhemp | United States (Missouri) | ALS inhibitors – HRAC Group 2 |
| 18 | 1994 | Xanthium strumarium | Common Cocklebur | United States (North Carolina) | Nucleic acid inhibitors – HRAC Group 17 |
| 19 | 1994 | Amaranthus palmeri | Palmer Amaranth | United States (Tennessee) | ALS inhibitors – HRAC Group 2 |
| 20 | 1997 | Sorghum halepense | Johnsongrass | United States (Louisiana) | ACCase inhibitors – HRAC Group 1 |
| 21 | 1997 | Amaranthus palmeri | Palmer Amaranth | United States (South Carolina) | ALS inhibitors – HRAC Group 2 |
| 22 | 1998 | Amaranthus palmeri | Palmer Amaranth | United States (Tennessee) | Microtubule Assembly inhibitors – HRAC Group 3 |
| 23 | 2001 | Conyza canadensis | Horseweed | United States (Tennessee) | EPSPS inhibitors – HRAC Group 9 |
| 24 | 2002 | Conyza canadensis | Horseweed | United States (Missouri) | EPSPS inhibitors – HRAC Group 9 |
| 25 | 2003 | Conyza canadensis | Horseweed | United States (Arkansas) | EPSPS inhibitors – HRAC Group 9 |
| 26 | 2003 | Conyza canadensis | Horseweed | United States (Mississippi) | EPSPS inhibitors – HRAC Group 9 |
| 27 | 2003 | Conyza canadensis | Horseweed | United States (North Carolina) | EPSPS inhibitors – HRAC Group 9 |
| 28 | 2005 | Sorghum halepense | Johnsongrass | Greece | ACCase inhibitors – HRAC Group 1 |
| 29 | 2005 | Digitaria insularis | Sourgrass | Paraguay | EPSPS inhibitors – HRAC Group 9 |
| 30 | 2005 | Amaranthus palmeri | Palmer Amaranth | United States (Georgia) | EPSPS inhibitors – HRAC Group 9 |
| 31 | 2005 | Conyza canadensis | Horseweed | United States (Kansas) | EPSPS inhibitors – HRAC Group 9 |
| 32 | 2005 | Lolium perenne ssp. multiflorum | Italian Ryegrass | United States (Mississippi) | EPSPS inhibitors – HRAC Group 9 |
| 33 | 2005 | Amaranthus palmeri | Palmer Amaranth | United States (North Carolina) | EPSPS inhibitors – HRAC Group 9 |
| 34 | 2006 | Sorghum halepense | Johnsongrass | Israel | ACCase inhibitors – HRAC Group 1 |
| 35 | 2006 | Ambrosia artemisiifolia | Common Ragweed | United States (North Carolina) | EPSPS inhibitors – HRAC Group 9 |
| 36 | 2006 | Amaranthus palmeri | Palmer Amaranth | United States (Arkansas) | EPSPS inhibitors – HRAC Group 9 |
| 37 | 2006 | Amaranthus palmeri | Palmer Amaranth | United States (South Carolina) | EPSPS inhibitors – HRAC Group 9 |
| 38 | 2006 | Amaranthus palmeri | Palmer Amaranth | United States (Tennessee) | EPSPS inhibitors – HRAC Group 9 |
| 39 | 2006 | Amaranthus tuberculatus | Tall Waterhemp | United States (Texas) | EPSPS inhibitors – HRAC Group 9 |
| 40 | 2007 | Kochia scoparia | Kochia | United States (Kansas) | EPSPS inhibitors – HRAC Group 9 |
| 41 | 2007 | Ambrosia trifida | Giant Ragweed | United States (Tennessee) | EPSPS inhibitors – HRAC Group 9 |
| 42 | 2008 | Amaranthus palmeri | Palmer Amaranth | Israel | ALS inhibitors – HRAC Group 2 |
| 43 | 2008 | Echinochloa colona | Junglerice | United States (California) | EPSPS inhibitors – HRAC Group 9 |
| 44 | 2008 | Amaranthus palmeri | Palmer Amaranth | United States (Georgia) | Multiple resistance – ALS + EPSPS |
| 45 | 2008 | Amaranthus palmeri | Palmer Amaranth | United States (Mississippi) | Multiple resistance – ALS + EPSPS |
| 46 | 2008 | Amaranthus palmeri | Palmer Amaranth | United States (Missouri) | EPSPS inhibitors – HRAC Group 9 |
| 47 | 2009 | Lolium perenne ssp. multiflorum | Italian Ryegrass | United States (North Carolina) | EPSPS inhibitors – HRAC Group 9 |
| 48 | 2009 | Amaranthus tuberculatus | Tall Waterhemp | United States (Missouri) | Multiple resistance – ALS + EPSPS |
| 49 | 2009 | Amaranthus palmeri | Palmer Amaranth | United States (Tennessee) | Multiple resistance – ALS + EPSPS |
| 50 | 2010 | Echinochloa colona | Junglerice | Australia (Western Australia) | EPSPS inhibitors – HRAC Group 9 |
| 51 | 2010 | Amaranthus palmeri | Palmer Amaranth | United States (Louisiana) | EPSPS inhibitors – HRAC Group 9 |
| 52 | 2010 | Eleusine indica | Goosegrass | United States (Mississippi) | EPSPS inhibitors – HRAC Group 9 |
| 53 | 2010 | Amaranthus palmeri | Palmer Amaranth | United States (South Carolina) | Multiple resistance – ALS + EPSPS |
| 54 | 2011 | Amaranthus retroflexus | Redroot Pigweed | Brazil | Multiple resistance – ALS + PSII |
| 55 | 2011 | Amaranthus viridis | Slender Amaranth | Brazil | Multiple resistance – ALS + PSII |
| 56 | 2011 | Digitaria sanguinalis | Large Crabgrass | China | ACCase inhibitors – HRAC Group 1 |
| 57 | 2011 | Amaranthus palmeri | Palmer Amaranth | United States (Kansas) | EPSPS inhibitors – HRAC Group 9 |
| 58 | 2011 | Conyza canadensis | Horseweed | United States (Kansas) | ALS inhibitors – HRAC Group 2 |
| 59 | 2011 | Amaranthus tuberculatus | Tall Waterhemp | United States (Tennessee) | EPSPS inhibitors – HRAC Group 9 |
| 60 | 2011 | Amaranthus palmeri | Palmer Amaranth | United States (Texas) | EPSPS inhibitors – HRAC Group 9 |
| 61 | 2012 | Amaranthus retroflexus | Redroot Pigweed | Brazil | ALS inhibitors – HRAC Group 2 |
| 62 | 2012 | Amaranthus palmeri | Palmer Amaranth | United States (Arizona) | Multiple resistance – ALS + EPSPS |
| 63 | 2012 | Amaranthus spinosus | Spiny Amaranth | United States (Mississippi) | EPSPS inhibitors – HRAC Group 9 |
| 64 | 2013 | Ageratum conyzoides | Tropical Whiteweed | Brazil | ALS inhibitors – HRAC Group 2 |
| 65 | 2013 | Conyza canadensis | Horseweed | United States (Alabama) | EPSPS inhibitors – HRAC Group 9 |
| 66 | 2013 | Ambrosia artemisiifolia | Common Ragweed | United States (Alabama) | EPSPS inhibitors – HRAC Group 9 |
| 67 | 2013 | Amaranthus palmeri | Palmer Amaranth | United States (Florida) | EPSPS inhibitors – HRAC Group 9 |
| 68 | 2013 | Amaranthus spinosus | Spiny Amaranth | United States (Mississippi) | ALS inhibitors – HRAC Group 2 |
| 69 | 2014 | Amaranthus retroflexus | Redroot Pigweed | Brazil | PPO inhibitors – HRAC Group 14 |
| 70 | 2014 | Sonchus oleraceus | Annual Sowthistle | Australia (New South Wales) | EPSPS inhibitors – HRAC Group 9 |
| 71 | 2014 | Lolium perenne ssp. multiflorum | Italian Ryegrass | United States (Louisiana) | EPSPS inhibitors – HRAC Group 9 |
| 72 | 2015 | Amaranthus tuberculatus | Tall Waterhemp | United States (Arkansas) | EPSPS inhibitors – HRAC Group 9 |
| 73 | 2015 | Amaranthus tuberculatus | Tall Waterhemp | United States (Louisiana) | EPSPS inhibitors – HRAC Group 9 |
| 74 | 2015 | Amaranthus palmeri | Palmer Amaranth | Brazil | EPSPS inhibitors – HRAC Group 9 |
| 75 | 2016 | Amaranthus palmeri | Palmer Amaranth | Brazil | Multiple resistance – ALS + EPSPS |
| 76 | 2016 | Amaranthus palmeri | Palmer Amaranth | United States (Arkansas) | Multiple resistance – 5 herbicide groups |
| 77 | 2016 | Amaranthus palmeri | Palmer Amaranth | Mexico | EPSPS inhibitors – HRAC Group 9 |
| 78 | 2017 | Eleusine indica | Goosegrass | Brazil | Multiple resistance – ACCase + EPSPS |
| 79 | 2017 | Sorghum halepense | Johnsongrass | Israel | ALS inhibitors – HRAC Group 2 |
| 80 | 2018 | Conyza canadensis | Horseweed | United States (Oklahoma) | ALS inhibitors – HRAC Group 2 |
| 81 | 2018 | Amaranthus palmeri | Palmer Amaranth | South Africa | Multiple resistance – ALS + EPSPS |
| 82 | 2019 | Amaranthus tuberculatus | Tall Waterhemp | Israel | ALS inhibitors – HRAC Group 2 |
| 83 | 2020 | Amaranthus palmeri | Palmer Amaranth | United States (Arkansas) | Glutamine Synthetase inhibitors – HRAC Group 10 |
| 84 | 2020 | Amaranthus palmeri | Palmer Amaranth | United States (Tennessee) | Multiple resistance – EPSPS + Auxin Mimics |
| 85 | 2022 | Amaranthus palmeri | Palmer Amaranth | United States (North Carolina) | Glutamine Synthetase inhibitors – HRAC Group 10 |
| 86 | 2023 | Amaranthus palmeri | Palmer Amaranth | United States (Arkansas) | Auxin Mimics – HRAC Group 4 |
| 87 | 2017 | Eleusine indica | Goosegrass | Brazil | ACCase + EPSPS resistance |
Most Frequently Reported Herbicide-Resistant Weed Species in Cotton
| Rank | Weed Species | Common Name | Approximate Number of Reports |
|---|---|---|---|
| 1 | Amaranthus palmeri | Palmer Amaranth | Most frequent globally |
| 2 | Eleusine indica | Goosegrass | Widely reported in US and Brazil |
| 3 | Conyza canadensis | Horseweed | Multiple US states |
| 4 | Amaranthus tuberculatus | Tall Waterhemp | Major weed in US cotton systems |
| 5 | Sorghum halepense | Johnsongrass | Several countries including US and Greece |
| 6 | Xanthium strumarium | Common Cocklebur | Early resistance cases in US |
Palmer amaranth clearly dominates resistance reports and has become one of the most problematic weeds in cotton globally due to its rapid growth, high seed production and ability to develop resistance to multiple herbicide groups.
Herbicide Groups Most Affected by Resistance in Cotton
| HRAC Group | Herbicide Mode of Action | Examples | Resistance Frequency |
|---|---|---|---|
| Group 9 | EPSPS inhibitors | Glyphosate | Most common globally |
| Group 2 | ALS inhibitors | Imazethapyr, Chlorimuron | Very common |
| Group 3 | Microtubule inhibitors | Trifluralin | Early resistance cases |
| Group 1 | ACCase inhibitors | Clethodim, Fluazifop | Moderate |
| Group 14 | PPO inhibitors | Fomesafen | Increasing |
| Group 4 | Auxin mimics | 2,4-D, Dicamba | Recent cases |
| Group 10 | Glutamine synthetase inhibitors | Glufosinate | Emerging resistance |
Glyphosate resistance remains the most widespread problem, particularly due to the extensive use of glyphosate-tolerant cropping systems.
Implications for Cotton Production
The rapid spread of herbicide-resistant weeds has major implications for global cotton production. Farmers are facing higher weed management costs, increased herbicide applications and in some cases reduced crop yields. The emergence of weeds resistant to multiple herbicide groups further reduces available chemical control options.
To address this challenge, agronomists increasingly recommend integrated weed management strategies. These include rotating herbicide modes of action, using herbicide mixtures, adopting crop rotation and cover crops, and integrating mechanical weed control methods. Monitoring weed populations and early detection of resistance are also critical for preventing the spread of resistant weeds.
As cotton production continues to intensify globally, managing herbicide resistance will remain a key priority for researchers, extension specialists and farmers. Sustainable weed management practices that combine chemical and non-chemical approaches will be essential to maintain effective weed control in cotton systems in the coming decades.
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