Horseweed, or marestail, as it’s more commonly known, can present major problems for your row-crop operation if it is ignored during the winter. A single plant can produce 200,000 seeds, and more than 90% of horseweed that emerges in the fall can survive until springtime.¹
You can combat this prolific problem child and its herbicide resistance issues through post-harvest scouting and an effective burndown strategy.
How to get rid of horseweed: Understanding overwintering survival mechanisms
Horseweed’s life cycle makes it particularly pernicious during the winter months. It all starts during late summer and fall, when horseweed seeds germinate.
The plant survives during winter as basal rosettes, which are pubescent, club-shaped leaves that grow to about 3” long.² This gives them a massive head start that can complicate spring burndown efforts in no-till fields, as stems can grow to 6’ tall.
Horseweed control and herbicide resistance
Getting ahead of horseweed is especially important because glyphosate resistance in this weed species is particularly widespread. In fact, horseweed was one of the first weeds to develop resistance to glyphosate.
The weed spreads far and wide rapidly via wind-blown seeds, so it’s critical to use multiple sites of action to mitigate the spread of resistance before the weed bolts, along with other best management practices such as the use of cover crops.
Impact of weather conditions on burndown timing for horseweed control
For effective horseweed control, keep some important nuances in mind. Mild winter and spring weather can trigger early weed growth. This can happen below 50 F, which is too cool for herbicides to activate effectively. As a result, horseweed can bolt and easily outgrow spring burndowns.
A common management timeline starts with the use of effective herbicides in the fall followed by a burndown herbicide with residuals in the spring.³
Follow label directions carefully to optimize your weed control throughout the fall, winter and early spring. Use the right carrier type, volume and nozzle. Try to apply herbicide on sunny days with warm temperatures above 40 F throughout the day and night for best results.⁴ Prioritize any no-till fields, as horseweed grows most aggressively in this type of environment.
Work with your trusted adviser to evaluate the BASF herbicide portfolio for several effective products to manage horseweed.
How to kill horseweed: The value of early spring scouting
Your post-harvest weed management should only be one phase of your horseweed control strategy. It’s important to get back into the field in early spring to identify dense monocultures of overwintered rosettes while they are still small.
Spring burndown can avoid an out-of-control situation in which the weed’s unbranched stems bolt and elongate just as you prepare to plant your next corn or soybean crop.
Whether you call it horseweed or marestail, experts are available to help you sort out herbicide and other management decisions. Reach out to your seed retailer, a nearby extension office agent or a seed company professional like your regional BASF representative.
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Endnotes
- Ikley, Joe. “Horseweed.” Ag Hub, North Dakota State University,https://www.ndsu.edu/agriculture/ag-hub/horseweed. Accessed 1 Oct. 2026.
- Hartzler, Bob, and Meaghan Anderson. “Horseweed (Marestail).” Integrated Crop Management, Iowa State University Extension and Outreach, 8 June 2026,https://crops.extension.iastate.edu/encyclopedia/horseweed-marestail. Accessed 1 Oct. 2026.
- Loux, Mark, and Bill Johnson. “Control of Marestail in No-till Soybeans.” The Ohio State University and Purdue Extension Weed Science,https://ag.purdue.edu/btny/purdueweedscience/wp-content/uploads/2021/02/marestail-fact-2014-latest.pdf. Accessed 1 Oct. 2026.
- Anderson, Meaghan. “Weeds Took Advantage of a Mild Winter.” Integrated Crop Management, Iowa State University Extension and Outreach, 12 Mar. 2024,https://crops.extension.iastate.edu/cropnews/2024/03/weeds-took-advantage-mild-winter. Accessed 1 Oct. 2026.
