Field Facts: Marestail
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Marestail is a herbicide-resistant weed found across the Midwest. The weed typically begins its growing season in the fall, survives over winter and is still present in spring. It can also start its growing season in spring. So, burndown applications are important for controlling marestail, especially because it’s capable of reducing soybean yield by up to 80%.1
- Common names: Marestail, horseweed, Canada fleabane
- Scientific name: Conyza canadensis 2
- Cotyledons: Small, round
- Leaf shape: Lance-shaped
- Central, flowering stalk with hairs
- Flowers: Clustered, small and white
- Reproduction: Seeds
Fast facts
- If left to flourish, marestail can rob soybean yield of up to 80%.1
- Marestail can grow up to 6 feet tall. Once a plant grows up to 5 inches, control becomes much more difficult.3
- Each plant can produce 200,000 seeds per plant — which are spread primarily by wind — that can travel to neighboring farms and even nearby states.3
- Marestail can begin its growing season in fall or spring. Plants that emerge in the fall can survive the winter and continue growing as the row crop emerges.3
- Marestail begins its growth cycle as a small rosette between 1 to 4 inches across. While scouting, it is important to look beneath debris because the plants may otherwise remain hidden.4
- Many states in the Midwest are fighting the ever-growing population of marestail that is resistant to glyphosate and ALS-inhibiting herbicides.4
- According to International Herbicide-Resistant Weed Database, the first confirmation of glyphosate-resistant marestail was in Delaware in 2000. Since then, resistance has spread to crops in 24 states.
Control tips
- A herbicide program approach that includes burndown applications, multiple passes, several modes of action and residual activity is good for controlling marestail in both corn and soybeans.
- Applying a burndown in fall or early spring is very important for controlling marestail, because it becomes increasingly difficult to control as it grows larger. Elevore® herbicide provides excellent burndown control.
- In corn, a good preemergence choice is SureStart® II herbicide followed by a timely postemergence application of Resicore® herbicide.
- In soybeans, a good option for a preemergence is Kyber™ herbicide followed by a postemergence application of EverpreX® herbicide. For Enlist E3® soybeans, applying Kyber preemergence followed by Enlist One® herbicide or Enlist Duo® herbicide postemergence works well against marestail.
- Planting corn and/or small grains in rotation can help control marestail. The canopy of corn can suppress growth, while small grains can be highly competitive. 2
1Integrated Crop Management News and Iowa State University Extension and Outreach 2021. 2020 Summary of Herbicide Evaluations for Marestail (Horseweed) Control in Soybeans. https://crops.extension.iastate.edu/cropnews/2021/02/2020-summary-herbicide-evaluations-marestail-horseweed-control-soybean
2Integrated Crop Management News and Iowa State University Extension and Outreach 2017. Fall Marestail (Horseweed) Management. https://crops.extension.iastate.edu/cropnews/2017/10/fall-marestail-horseweed-management
3Penn State Extension 2017. Marestail (Horseweed) Management. https://extension.psu.edu/marestail-horseweed-management
4Nebraska Institute of Agriculture and Natural Resources 2016. Fall is Optimal for Marestail Management. https://cropwatch.unl.edu/2016/fall-optimal-marestail-management
The transgenic soybean event in Enlist E3® soybeans is jointly developed and owned by Corteva Agriscience LLC and MS Technologies, L.L.C. Enlist Duo® and Enlist One® herbicides are not registered for sale or use in all states or counties. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your area. Enlist Duo and Enlist One herbicides are the only 2,4-D products authorized for use with Enlist® crops. Consult Enlist herbicide labels for weed species controlled. Elevore®, EverpreX®, Kyber™, Resicore® and SureStart® II are not registered for sale or use in all states. Resicore and SureStart II are not available for sale, distribution or use in Nassau and Suffolk counties in the state of New York. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Consult the label before purchase or use for full details. Always read and follow label directions.