Palmer amaranth is one of the most competitive weeds in corn and soybean fields across the United States. The weed is capable of reducing soybean yield by nearly 80% and corn yield by more than 90%.1 Palmer amaranth is also highly adaptive; herbicide-resistant populations of the weed have been found in more than half of the 50 states.
- Common name: Palmer amaranth
- Scientific name: Amaranthus palmeri
- Cotyledons: Long and narrow
- Leaf shape: Leaves are ovular or diamond-shaped, smooth and arranged in an alternate pattern. Leaves may have a sharp spine at their tips.
- Stems: Smooth
- Flowers: Female flowers have large bracts (up to ¼ inch long) that can become sharp, making the seed heads painful to handle.2
- Palmer amaranth is native to the southwestern United States, but it has spread to several areas of the country, including the Midwest.
- Palmer amaranth is now considered the most competitive weed in Midwest fields and is capable of reducing soybean yield by nearly 80% and corn yield by more than 90%.1
- The weed is so competitive, in part, because it grows very fast. Palmer amaranth can grow by as much as 2½ inches per day.3
- Palmer amaranth is dioecious, meaning male and female flowers grow on different plants. This trait increases the weed’s genetic diversity, allowing it to more easily develop herbicide resistance.3
- One female Palmer amaranth can produce up to 600,000 seeds.3
- Populations of Palmer amaranth have shown resistance to five herbicide groups. Those are Group 2 (ALS inhibitors), Group 3 (microtubule assembly inhibitors), Group 9 (EPSP synthase inhibitors), Group 14 (PPO inhibitors) and Group 27 (HPPD inhibitors).
- According to the International Herbicide-Resistant Weed Database, 29 states have reported populations of herbicide-resistant Palmer amaranth in crops.
- As with all herbicide-resistant weeds, a program approach that includes a burndown and pre- and postemergence residual herbicide applications with multiple modes of action can control Palmer amaranth.
- In corn, a good preemergence option is SureStart® II herbicide, followed by a timely postemergence application of Resicore® herbicide. Resicore® XL herbicide, when it becomes available, will also be a good choice for pre- or postemergence control. The new product is currently on track for registration from the U.S. Environmental Protection Agency in 2022.
- In soybeans, a good preemergence option to use is Kyber™ herbicide, followed by a postemergence application of DuPont™ EverpreX® herbicide. For Enlist E3® soybeans, applying Kyber preemergence followed by a postemergence of Enlist One® herbicide plus Liberty herbicide or Enlist Duo® herbicide works well against Palmer amaranth. According to 2020 Corteva Agriscience trials, a tank mix of Enlist One plus Liberty provided 91% control of Palmer amaranth.
- Cultural practices also can help keep Palmer amaranth under control. Some of those practices include:
- Crop rotation, which allows farmers to use herbicides with different modes of action in the field. Rotating to cereal rye is a good idea, as this crop can provide a mulch that helps suppress Palmer amaranth.
- Practicing deep tillage, which can bury the small Palmer amaranth seeds below their preferred emergence depth.
- Harvesting heavily infested fields last, because machinery easily spreads Palmer amaranth seeds from one field to another. Harvesting infested fields last lessens the possibility of spreading those seeds to uninfested fields.
1Hager, A. 2018. Remain Vigilant for Palmer Amaranth. https://farmdocdaily.illinois.edu/2018/07/remain-vigilant-for-palmer-amaranth.html
2Hartzler, B. 2021. Palmer amaranth: ID, biology and management. https://crops.extension.iastate.edu/encyclopedia/palmer-amaranth-id-biology-and-management
3United Soybean Board. 2021. Palmer amaranth. https://iwilltakeaction.com/weed/palmer-amaranth
4Corteva Agriscience field trials, 2020. Control of 3- to 4-inch Palmer amaranth with Enlist One® herbicide at 32 fluid ounces, Liberty® herbicide at 32 fl. oz., glyphosate DMA at 29 fl. oz. and AMS at 2.5 v/v.
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. Resicore® XL has not yet received regulatory approvals; approvals are pending. The information presented here is not an offer for sale. 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. Liberty is a registered trademark of BASF. 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.