Today, waterhemp is known as one of the worst weeds Midwest farmers have to tangle with each season, but it wasn’t always this way. Native to North America, waterhemp was just a plant that kept more to marshy areas than farm fields. In the last 25 to 30 years, however, waterhemp populations have exploded.
- 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 1/8-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)
- Waterhemp is a prolific seed producer and able to produce as many as 1.5 times more seeds than most other pigweed species.
- Waterhemp plants generally produce about 250,000 seeds per plant, although some plants can produce 1 million or more seeds under optimum conditions in noncompetitive environments.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.
The chances of waterhemp evolving resistance to herbicides that utilize a single mode of action is very high. That’s why it’s important to implement a program approach that incorporates multiple modes of action.
- A program approach 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 herbicide options from the Corteva Agriscience™ portfolio include Resicore® herbicide, SureStart® II herbicide and Realm® Q herbicide.
- For soybeans, consider Trivence® herbicide.
- Use between seven and nine modes of action over a two-year rotation cycle.
In addition to using a strategic combination of herbicides, there are 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.
1 United Soybean Board. 2020. Waterhemp. https://iwilltakeaction.com/weed/common-waterhemp.
Realm® Q, Resicore®, Sonic®, SureStart® II and Trivence® 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.