Strategies for Palmer Amaranth Control in Corn and Soybeans

Palmer amaranth is one of the most aggressive and costly weeds in U.S. row crops.
If you’re growing corn or soybeans, you know this weed can outcompete your crops, reduce yields, and develop resistance to herbicides faster than almost any other species. The good news is that a proactive, diversified management strategy can protect your crops from this destructive weed.

Cultural practices for Palmer amaranth control in corn and soybeans

Narrow row spacing

When crops like soybeans are planted closer together, the canopy will close sooner. Palmer amaranth thrives in open areas, so a closed canopy can prevent late-season emergence. This narrow spacing can be especially helpful in hot and dry climates where soybeans grow more slowly and the open areas of a field become prone to Palmer amaranth outbreaks.¹

Crop rotation

Continuous corn or soybeans limits the types of strategies you can implement on your fields. When you rotate soybeans with different crop families, including corn and small grains like wheat, you can disrupt the life cycle of Palmer amaranth with different planting and harvest timing.² You can also rotate to different modes of action for herbicide applications that would be unavailable in continuous corn or soybeans.³

Cover crops

Palmer amaranth weeds aren’t very tolerant of shade and often need open areas with full sun to thrive. Additionally, they prefer disturbed areas to grow. Keeping soil covered with a cover crop that accumulates high biomass levels (preferably more than 7500 lbs dry biomass per acre) can significantly reduce the seed germination of Palmer amaranth. Cover crops of this type include cereal rye, wheat, or hairy vetch. A delayed termination and early fall cover crop planting can optimize the effect.⁴

Herbicide strategies for Palmer amaranth control in corn and soybeans

Start clean

Equipment can be one of the leading spreaders of Palmer amaranth seed. So, if you’re coming from a field that has a history of Palmer amaranth, make sure everything is clean. Then, start your fields with a weed-free seedbed. That means either tilling under or using a burndown herbicide if you are no-till. A weed-free bed will make your weed management much easier later in the growing season.⁵
Using Sharpen® herbicide as a burndown prior to planting will control small, emerged Palmer amaranth and provide soil residual.

Pre-plant or pre-emergence application

Once you have a clean seedbed, apply a pre-emergence herbicide to delay and prevent weed seed germination. Make sure treatments are as close to planting as possible, as applications earlier than 1-2 weeks before planting are less effective. ⁶

Timely post-emergence applications

Even with strong pre-emergence control, Palmer amaranth can still break through. That’s why timely post-emergence herbicide applications are essential. The key is to apply herbicides when Palmer amaranth is still small, less than 3-4 inches tall. At this stage, it’s much more vulnerable to control, and delaying treatment can result in poor herbicidal efficacy and little control over weed seed production. Apply about 3-4 weeks after planting soybeans and 4-5 weeks after planting corn.⁷

Liberty® Ultra herbicide can by used in LibertyLink® corn and soybeans with the LibertyLink trait such as Xitavo® or E3 soybeans.

Residual herbicides

Including a residual herbicide in your post-emergence pass helps extend control until there is adequate canopy closure. This reduces the chance of late-season flushes, especially in fields where canopy development is slower due to drought or wider row spacing. Applying layered residuals at planting and then another during post-emergence gives your crop the competitive edge it needs during the critical weed-free period.⁸

Both Outlook® and Zidua® herbicides can be used post in corn and soybeans providing residprotection from Palmer amaranth and many other weeds.

Mechanical practices for Palmer amaranth control in corn and soybeans

Tillage

Due to Palmer amaranth’s ability to develop resistance to herbicides, mechanical control can often give your weed management an added boost. Deep tillage with a moldboard plow every 3-4 years can bury weed seeds deep enough so they won’t germinate. Studies have shown that deep tillage can reduce the emergence of pigweed species, like Palmer amaranth, by up to 73%.⁹
However, it’s important to remember that Palmer amaranth seeds can survive for several years in the soil. If you use tillage, avoid bringing buried seeds back to the surface in future passes by limiting disturbance to the top 1–2 inches. Using shallow tillage or setting implements to a consistent depth can help leave deeper seeds undisturbed. Tillage can be especially helpful in fields with heavy infestations or where herbicide resistance is already a concern.

Hand pulling

If you have a few weeds that have escaped your previous control methods, hand pulling can be an effective resort. Plants can produce hundreds of thousands of seeds if left unchecked, so removing even a few before they go to seed can make a big difference. Just be sure to remove plants completely from the field. Don’t just toss them into the row, as they may still drop seed.

Palmer amaranth is not just another weed; it is a threat to long-term profitability and sustainability. By taking a proactive, multi-faceted approach now, farmers can protect their yields, reduce resistance risk, and stay ahead of one of agriculture’s most aggressive invaders.

Experts are available to help you make your 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

1. Temple, Laura. “Integrated Weed Management Effectively Fights Resistance.” Soybean Research & Information Network, July 2021, https://soybeanresearchinfo.com/research-highlight/integrated-weed-management-effectively-fights-resistance/
2. VanGessel, Mark and Quintin Johnson. “Palmer Amaranth Control in Crop Land.” University of Delaware Cooperative Extension, 2019, https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/weed-science/WF21-PalmerAmaranth_19.pdf
3. Temple. “Integrated Weed Management Effectively Fights Resistance.”
4. Scruggs, Eric, Michael Flessner, and David Holshouser. “Palmer Amaranth (Amaranthus palmeri) Control in Soybeans.” Virginia Cooperative Extension, Virginia Tech, 2020. https://www.pubs.ext.vt.edu/2808/2808-1006/2808-1006.html
5. VanGessel and Johnson. “Palmer Amaranth Control in Crop Land.”
6. VanGessel and Johnson. “Palmer Amaranth Control in Crop Land.”
7. VanGessel and Johnson. “Palmer Amaranth Control in Crop Land.”
8. VanGessel and Johnson. “Palmer Amaranth Control in Crop Land.”
9. Farmer, Jaime A., et al. “Influence of tillage method on management of Amaranthus species in soybean.” Weed Technology 31.1 (2017): 10-20.