- Various types: Common,1 tall
- Scientific name: Amaranthus rudis1
- Grass or broadleaf: Small-seeded broadleaf
- Found in: AL, AR, CA, CO, CT, DE, GA, IA, ID, IL, IN, KS, KY, LA, MA, ME, MI, MN, MO, MS, NC, ND, NE, NH, NJ, NM, NY, OH, OK, PA, SC, SD, TN, TX, VT, WA, WI, WV2
- Germination timing: Summer annual; waterhemp germination and emergence extend late into the growing season.2
- Competitiveness: Highly competitive, especially with soybeans; research has shown waterhemp can cause up to 40 percent soybean yield loss.2
- Waterhemp is one of the most common weeds Midwest growers face every season. A number of factors — reduced-tillage systems, herbicide-resistant biotypes and simplified weed management systems — contributed to the rise of waterhemp problems in the late 1980s and early 1990s.3
- Waterhemp has small seeds that can only emerge from shallow depths, placing no-till fields at greater risk for growth.3
- Common waterhemp is a slender, willowy plant with many branches. Mature plants range from 4 inches to 12 feet in height.3
- The species can be identified by its brightly colored leaves, varying from deep red or pink to emerald green. Its stems, leaves and seed head all may be differently colored on a single individual plant. Stems and leaves are very smooth and hairless with a bright, glossy appearance. Leaves are long and narrow.
- Waterhemp biotypes have developed resistance to multiple herbicide modes of action, which presents challenges for row-crop growers.
According to WeedScience.org:
Multiple resistance: two sites of action
Multiple resistance: three sites of action
Multiple resistance: four sites of action
- ALS inhibitors, Photosystem II inhibitors, HPPD inhibitors and EPSP synthase inhibitors
*Resistance confirmation does not necessarily include all weeds and may vary among different areas of each state.
Weed management tips:
Scott Ditmarsen, field scientist, Dow AgroSciences, says:
- High-volume seed producer. Waterhemp germinates throughout the growing season and is very competitive because of the volume of seeds it produces and its rapid growth rate.
- Waterhemp seeds can survive several years in the soil.
- Use a guide to identify the weed species. Waterhemp can be difficult to properly identify at early growth stages because it is a member of the pigweed (Amaranthus) family, along with Palmer amaranth and redroot pigweed. These species tend to have similar characteristics. Consulting a university weed identification guide can help identify which species is in a field.
- Waterhemp stems are hairless, while other pigweed species have hairy stems. Cotyledons usually are more egg-shaped than the longer and narrower cotyledons of other pigweed species, while the first true leaves of waterhemp typically are longer and more lance-shaped than those of other pigweeds. Also, waterhemp seedlings are hairless with shiny or waxy leaves.
- Early control is critical. Scout throughout the growing season to identify waterhemp early to ensure timely herbicide applications.
- Aggressive tillage and a program approach using preemergence herbicides followed by postemergence herbicides with multiple modes of action is the best strategy to control waterhemp. Consider using Resicore™ herbicide in corn or Sonic® herbicide in soybeans preemergence to control waterhemp into the growing season.
- Any cultural practices that improve crop competitiveness will improve the effectiveness of herbicide programs. Physical removal of escaped plants to reduce competition and seed production, when feasible, also is recommended.
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:
- Biology & Management of Waterhemp — Purdue University Extension
- Waterhemp has emerged in Minnesota — University of Minnesota Extension