- Common name: Tall waterhemp, common waterhemp
- Scientific name: Amaranthus rudis
- Grass or broadleaf: Annual broadleaf
- Member of the pigweed family
- Native to North America, specifically the Midwest, but can range from the western Southwest to East Coast.
- Even though waterhemp flourishes in wet areas of land, it has become adaptable to other conditions.1
- Seeds can germinate throughout the growing season and, if not controlled early, the plant can produce anywhere between 300,000 to 500,000 seeds per plant with a possibility of up to a million seeds. Proliferation can result in substantial yield loss.2
- Plants emerge throughout the growing season, with some not germinating until later in the season. This can make it difficult for farmers to spray and control them as they may arise after first spraying has taken place. However, late-emerging plants produce smaller amounts of seeds that have low impact on yield.3
Waterhemp facts that may surprise you
- Waterhemp is native to the United States and is now found in 40 states.
- Waterhemp that grows later in the season is generally waxier, making it harder to kill.4
- Waterhemp can only grow in shallow seed beds, making it a nightmare for no-till farmers.
- Waterhemp is a dioecious plant, meaning it has separate male and female plants. This can be a disadvantage for waterhemp as it then must find the counterpart to become reproductive.5
- Plants can range anywhere from 4 inches to 12 feet, but most are between 4 to 5 feet in agronomic settings.5
- You can distinguish between the male and female plants by rubbing the mature flowers between your fingers. If you find tiny black seeds, the plant is a female.5
- Waterhemp and weeds within the pigweed family can be hard to distinguish. Some ways to tell waterhemp apart is by its waxy/shiny appearance of leaves, hairless stem and leaf surfaces, egg-shaped cotyledons and alternate leaves.6
- During its growing season, waterhemp has the ability to grow 1.5 inches per day.
Waterhemp control/management tips
According to Scott Ditmarsen, field scientist, Dow AgroSciences:
- Waterhemp is a very prolific seeder and germinates throughout the growing season. It is a competitive weed due primarily to its sheer numbers and fast growth rate.
- Farmers should implement timely and effective scouting throughout the growing season to identify waterhemp early. This helps farmers plan timely herbicide applications and identify potential problem fields for the following year.
- Combining aggressive tillage and a program approach to weed control — including soil-applied herbicides followed by postemergence herbicide(s) with multiple, effective modes of action — is the best strategy to control waterhemp.
- When feasible, physically remove escaped waterhemp plants to reduce competition and seed production.
- Any cultural practices that improve crop competitiveness will improve the effectiveness of herbicide programs.
Dow AgroSciences weed control solutions:
SureStart® II herbicide
Keystone® NXT herbicide
Keystone® LA NXT herbicide
FulTime® NXT herbicide
Surpass® NXT herbicide
Durango® DMA® herbicide
Enlist Duo® herbicide, as part of the Enlist™ weed control system
More information can be found through these weed science resources:
Waterhemp has emerged; North Dakota State University
Are you ready for weeds?; University of Missouri
Management of ALS-resistant Palmer Amaranth and Waterhemp in the Panhandle; University of Nebraska
1North Dakota State University. 2017. Waterhemp has Emerged in 2017. https://www.ag.ndsu.edu/cpr/weeds/waterhemp-has-emerged-in-2017-5-18-17
2University of Missouri Integrated Pest Management. 2015. Are you ready for weeds? https://ipm.missouri.edu/ipcm/2015/9/Are-you-ready-for-the-weeds/
3Lawrence, N. 2017. Management of ALS-Resistant Palmer Amaranth and Waterhemp in the Panhandle.
4Gullickson, G. 2014. 22 Sobering Need-to-Know Facts About Herbicide-resistant Weeds. http://www.agriculture.com/crops/tech-tour/22-sobering-needtoknow-facts-about_196-ar42485
5Nordby, D., B. Hartzler, and K. Bradley. 2007. Biology and Management of Waterhemp.
6Werle, R., L. Sandell, and G. Kruger. 2013. Postemergence Control of Emerged Waterhemp in Soybeans.