Field Facts: Waterhemp
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Waterhemp has the unique ability to adapt to control tactics and has evolved resistance to multiple modes of action, making it one of the most challenging weeds that Midwest corn and soybean growers face today.
- Common names: Waterhemp, rough-fruit amaranth, tall waterhemp
- Scientific name: Amaranthus tuberculatus
- Cotyledons: Egg- to ovate-shaped
- Leaf shape: Lanceolate
- Stems: Hairless
- Flowers: Individual plants produce either staminate flowers (male) or pistillate flowers (female). Both types of flowers are less than ⅛ inch long. Each staminate flower consists of five sepals, five stamens and no petals; it is surrounded by one to three narrow bracts with pointed tips.
- Reproduction: Dioecious (male and female flowers on separate plants)
Fast facts
- Waterhemp is a prolific seed producer and able to produce as many as 1.5 times more seeds than most other pigweed species.
- Waterhemp grows more rapidly than most weeds or crops — typically about 1 to 1.25 inches per day during the growing season. This allows waterhemp seedlings to acquire more sunlight than other weeds.1
- A joint study written by professors from the University of Illinois, the University of Missouri and Iowa State University reports waterhemp can reduce soybean yield by up to 44% and corn yield by up to 15%.
- Cross-pollination allows for healthier populations. If either the male or female plant develop resistance, the offspring will carry the resistant trait moving forward.
- Waterhemp has an extended emergence period, which allows waterhemp plants to surface late in the growing season.
- Populations of waterhemp have shown resistance to many herbicide groups. According to the International Herbicide-resistant Weed Database, 20 states have reported populations of herbicide-resistant waterhemp in crops.
Control tips
The chances of waterhemp developing resistance to herbicides that utilize a single mode of action are very high. In fact, waterhemp has shown resistance to herbicides in seven herbicide groups to date.2 That’s why it’s important to implement a program approach that incorporates multiple modes of action — ideally between seven and nine modes of action over a two-year rotation cycle.
This means starting clean with a burndown, using powerful preemergence herbicides with residual activity and then using effective postemergence herbicides that also have residual activity. Key corn herbicides from the Corteva Agriscience portfolio include Resicore® XL herbicide, Kyro™ herbicide and SureStart® II herbicide. For soybeans, consider Kyber® herbicide, Sonic® herbicide and Enlist® herbicides.
In addition to using a strategic combination of herbicides, growers can use several cultural practices to help control waterhemp, such as:
- Planting soybeans in narrow rows to promote earlier row shading and discourage the growth of waterhemp.
- Deep tillage to reduce the amount of waterhemp seeds that germinate by burying them at unfavorable depths.
- Planting fall-seeded cover crops like cereal rye.
Work with your customers and your Corteva Agriscience representative to identify and implement best management practices for waterhemp and other yield-robbing weeds in your area.
1United Soybean Board. 2023. Waterhemp. https://iwilltakeaction.com/weed/common-waterhemp.
2Take Action. 2023 Weed Out Resistance. https://iwilltakeaction.com/uploads/files/20200921-factsheet-11threaten-poster-usdadraft.pdf
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. Kyber®, Kyro™, Resicore® XL, Sonic® and SureStart® II are not registered for use in all states. Kyro, Resicore XL 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.