| Welcome to the Home of |
| Horseweed |
| (Conyza canadensis) |
| www.btny.purdue.edu/weedscience |
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| Funding for our horseweed research and extension efforts has been provided by: |
| Indiana Soybean Board |
| Purdue University Ag Research Programs |
| Monsanto |
| Syngenta |
| Dow Agrosciences |
| BASF |
| Valent |
| Dupont |
| USDA Critical and Emerging Pest Program |
| Publications |
| Late-Season Weed Escapes in Indiana Soybean Fields - Crop Management Brief |
| Crop Rotation and Tillage System Influence Late- Season Incidence of - Giant Ragweed and Horseweed in Indiana Soybean - Crop Management Brief |
| Biology and Management of Horseweed - Extension Publication # 323 |
| Newsletter Articles |
| Glyphosate -Tolerant/Resistant Marestail is Widespread in Southeastern Indiana Counties |
| Update on the Occurrence of Glyphosate-Resistant Marestail/Horseweed |
| Identifying Glyphosate Resistant Marestail/Horseweed in the Field |
| Herbicide Resistant Horseweed/Marestail |
Horseweed ( Conyza canadensis ) is more commonly known as marestail to most Indiana farmers. Horseweed is native to the United States, but it has recently become much more problematic to control in Roundup Ready soybean production. Horseweed is well adapted to no-till crop production. It has developed resistance to several different herbicides including glyphosate products (www.weedscience.com). Horseweed was the first broadleaf weed documented to develop resistance to glyphosate (Vangessel 2001) in the United States. Since this initial report, glyphosate resistance has been reported in several other states including Indiana.
In Indiana , the first case of glyphosate resistance was confirmed in Jackson County in 2002. With 90% of the soybean acres planted to Roundup Ready varieties and 60% of soybeans grown utilizing no-till practices in Indiana, it is a high priority for the Purdue Weed Science Team to help Indiana soybean producers find the best alternatives to keep horseweed from becoming an even bigger threat to agriculture production and environmental quality.
The objective of this website is to provide information on the distribution, biology and management of glyphosate-resistant horseweed in Indiana and selected other states. The site contains frequently updated maps showing locations of glyphosate-resistant horseweed, and our latest research results on the biology and management of this weed. If you have any questions about this site or you have information and links you would like added to this site, please contact Vince Davis, Valerie Mock, Bill Johnson, or Glenn Nice.
Distribution of Glyphosate-Resistant Horseweed in Indiana and Ohio
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| Sites Surveyed - this page displays the intensity and location of Indiana counties that have been surveyed for horseweed escapes in 2003 through 2005. |
| Materials and Methods - this is a concise abstract on how the sample locations were determined and how samples were screened for resistance. For even more information, see the 2003 Survey Development poster, or the 2004 WSSA Horseweed Survey presentation. |
| IN Screening Results - this page is an interactive map of IN that allows users to find detailed information regarding the location of glyphosate resistant samples collected in the fall of 2003 through 2005. |
| IN and OH Screening Results - this page has a two state map showing counties with confirmed glyphosate resistant horseweed in both IN and OH. |
| Sampling Form - If you want to take action on horseweed escapes near you, this form is available for crop advisors and producers to use for collecting the proper information to submit a horseweed sample to the weed science department at Purdue University to confirm glyphosate resistance. |
| Horseweed Biology, Ecology, and Management |
| Biology and ecology of horseweed at Purdue results will be posted soon, but to learn more about the research currently being conducted, click here to read a master's thesis proposal by Vince Davis. |
| Horseweed response to glyphosate doses. Experiments have been conducted and are currently being repeated to study the response to ranging rates of glyphosate. To learn more visit the glyphosate dose-response on selected populations poster or abstract. |
| Horseweed response to other herbicides. Resistance to ALS inhibitors has been identified in several IN horseweed populations. ALS inhibitor dose-response experiments on selected populations, and initial ALS inhibitor and 2,4-D screening is currently being conducted in the greenhouse on all horseweed populations collected thus far. Initial greenhouse screens on over 450 populations should be completed by spring 2007. To learn more about these experiments, please check back later for results. |
| Horseweed management trials were conducted in 2003 and 2004. To learn more about those trials and their results, visit the 2003 efficacy of glyphosate tank mixes poster, presentation, or abstract. And, visit the 2004 control of GR Horseweed in corn and soybean with post herbicides poster or abstract. |
| I am concerned about controlling glyphosate-resistant horseweed, What should I do? - this page has the current Purdue recommendations for no-tillage soybean producers in southeastern IN. |
For more information regarding this web page please contact:
Vince Davis, Valerie Mock, Bill Johnson, or Glenn Nice.
This web site was posted on Sept. 15, 2004 and last updated on Sept. 11, 2006.