Waterhemp is a competitive weed in the pigweed (Amaranthus) family, along with Palmer amaranth, redroot pigweed, and other pigweed species. Read the latest news on waterhemp and find weed management information from Dow AgroSciences field scientist Scott Ditmarsen.
- Various types: Common1
- Scientific name: Amaranthus rudis1
- Grass or broadleaf: Small-seeded broadleaf1
- 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, WV1
- Germination timing: Summer annual; waterhemp germination and emergence extend late into the growing season2
- Competitiveness: Very competitive, especially with soybeans; previous research has shown waterhemp can cause up to 40 percent soybean yield loss2
- Common waterhemp is a slender, willowy plant with many branches. Mature plants range from 4 to 12 feet in height.
- 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.
- Its small seeds can only emerge from shallow depths, placing no-till fields at greater risk for waterhemp infestation.3
According to WeedScience.org:
- Herbicide classes
- Multiple resistance: two sites of action
- Multiple resistance: three sites of actions
*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:
- Waterhemp is a very prolific seeder. It germinates throughout the growing season and is very competitive due primarily to its sheer numbers and rapid growth rate.
- Although later-emerging waterhemp usually does not impact crop yield, it can produce a large amount of seed that can survive several years in the soil.
- Waterhemp biotypes have also developed resistance to multiple (herbicide) modes of action, which presents additional challenges.
- Identification of waterhemp can be difficult, especially at early growth stages, because it is a member of the pigweed (Amaranthus) family, along with Palmer amaranth, redroot pigweed and other pigweed species. These species tend to have similar characteristics. Consulting a weed identification guide can assist in properly identifying species in the field.
- Appearance. Waterhemp cotyledons (seed leaves) 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; the stems are hairless, while other pigweed species have hairy stems.
- Control. Timely and effective scouting throughout the growing season is required to identify waterhemp early to ensure timely herbicide applications and to identify potential problem fields for the following year.
- Aggressive tillage and a program approach involving soil-applied herbicides followed by postemergence herbicide applications using multiple, effective modes of action is the best strategy to control waterhemp.
- 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, is also recommended.
Dow AgroSciences weed control solutions:
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