Tall Waterhemp

Biological Name:

Amaranthus tuberculatus (Tall-Waterhemp)

Natural Habitat:

Tall-Waterhemp: Typically found in wetland and riparian habitats in the central and eastern United States.

Description:

Tall-Waterhemp also known as Amaranthus is a plant that is native to grassland and prairie regions of North America. It is an annual herb that can grow up to six feet tall and it has small oval-shaped leaves and small green or white flowers that bloom in the summer. The plant is known for its ability to grow quickly and aggressively and it is often considered a weed in agricultural fields.

Frequently Asked Questions (FAQs)

Q: How tall can waterhemp get?
A: Amaranthus tuberculatus Height: Can grow very tall, up to 10 feet in, especially in competition with corn. Flowers: Male and female flowers on separate plants. Flowers are primarily produced on long (up to 1-2 feet or more, in length) terminal flower heads. Female flowers do not have sharp bracts associated with them.
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Q: How fast does waterhemp grow?
A: Waterhemp grows more rapidly than most weeds or crops — typically about 1 to 1 ¼ inches per day during the growing season.
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Q: How do you control waterhemp in corn?
A: Atrazine, dicamba, 2-4,D, Callisto, Impact and Laudis are effective against waterhemp in corn. Soil-applied herbicides such as Dual, Surpass/Harness, Outlook and Zidua may also be effective. Going with soil-applied herbicides and not letting weeds get a head start is key now, Johnson says.
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Q: What does waterhemp do to corn?
A: In corn, Purdue researchers have found that a heavy waterhemp infestation early in the season can reduce yields by 15 percent. To minimize the economic impact of this potent weed, farmers have turned to a variety of expensive chemical cocktails.
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Q: How tall can horseweed grow?
A: Mature plants grow erect, 6-1/2 to 10 feet (2–3 m) tall. Usually a single main stem branches out from the upper half of the plant. In hairy fleabane , the main stem usually branches near the base. However, cutting the main stem of horseweed can lead to the growth of several basal branches.
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Q: How tall does pigweed get?
A: Mature plants may grow up to almost 10 feet (3 m) tall but in general are found growing to about 3 ft (1 m). The mature plants have coarse stems, and upper stems that range from hairy to densely hairy. Leaves generally range from 3/5 to 7 inches (1.5–17 cm) long and leaf stalks are 2/5 to 3 inches (1–8 cm) long.
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Q: What is the difference between pigweed and waterhemp?
A: Stems are hairless. Key ID traits: The stems of waterhemp are hairless, whereas redroot and smooth pigweed have hairs on stems. Leaves are lanceolate in shape and tend to be glossier than those of redroot and smooth pigweed. Waterhemp cotyledons are egg-shaped, whereas those of the pigweeds are more linear.
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Q: Should you pull pigweed?
A: If pigweeds are in the advanced reproductive stage and might drop viable seed when handled, carefully bagging plants is even more important, Farr and others say. Guy Collins, cotton Extension associate professor at North Carolina State University, also advocates hand pulling.
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Q: Why is pigweed so difficult to control?
A: The researchers have determined a specific genetic feature, the extrachromosomal circular DNA (eccDNA) replicon, gives pigweed, or glyphosate resistant palmer amaranth, its resistance to glyphosate and makes this weed difficult to control.
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Q: Why do they call it pigweed?
A: Their common name, pigweed, may have comes from its use as fodder for pigs. Pigweed plants are commonly considered to be weeds by farmers and gardeners because they thrive in disturbed soils.
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Q: What part of pigweed is poisonous?
A: Pigweed (Amaranthus retroflexus) is a common annual weed found throughout the United States. The weed can grow three to four feet; the flowers are green and prickly and the plant has oval shaped leaves. The pigweed’s leaves, roots and stems are toxic.
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Q: Is waterhemp a perennial or annual?
A: Biology. Waterhemp is a summer annual plant, relying upon yearly seed production for persistence. It is one of the few problematic dioecious weeds in US cropping systems, which means that male and female flowers occur on different plants.
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Q: How does waterhemp spread?
A: The seeds are small (approximately 3-mm in length) and can easily be transported by contaminated machinery, by waterfowl, through the spread of poultry litter as fertilizer, etc. Like most weeds, waterhemp seeds remain viable in the soil for several years.
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Q: How do you control a waterhemp?
A: For best control, apply a pre-emergence residual herbicide followed by post-emergence applications as needed throughout the growing season. Treating new infestations early reduces waterhemp establishment, prevents seed production and greatly improves control.
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Q: How many seeds can a waterhemp plant produce?
A: Reproduction: Female waterhemp plants can produce as many as 1 million seeds, but 35,000–200,000 seeds is more typical. Several populations produced 470,000–1.29 million seeds per plant in Indiana when established in May or June but produced 200,000–340,000 seeds when established in July.
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Q: Does celosia return year after year?
A: For gardeners that live in warm areas, your property could be perfect for growing celosia plants and having them come back year after year. In most other climates, you will find that your celosia plants need to be replanted again during the spring.
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Q: Is waterhemp poisonous?
A: About Waterhemp: This weed is poisonous for cattle, horses, sheep and goats when ingested.
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Q: Is waterhemp Roundup resistant?
A: The first confirmation of glyphosate-resistant waterhemp occurred in Platte County, Mo., in 2005. This waterhemp biotype was 19 times more resistant to glyphosate than a susceptible biotype and was confirmed to also be resistant to ALS- and PPO-inhibiting herbicides.
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Q: What is the difference between waterhemp and Palmer amaranth?
A: The Palmer amaranth leaf is much wider (horizontal arrows) and has a longer petiole (vertical arrows) than waterhemp. Palmer amaranth can be differentiated from waterhemp by its long petioles, causing the egg-shaped leaf blades to extend away from the stem.
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Q: What is the best amaranth to eat?
A: A pop of color can be important if you’re using amaranth as a microgreen or in a salad mix, especially for restaurant use. Try delicious A. tricolor ‘Red Leaf,’ with its thick burgundy foliage, or A. tricolor ‘Joseph’s Coat,’ which has striking red, green, and yellow leaves.
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Q: Why is amaranth called pigweed?
A: Today amaranth can be found almost everywhere from central Canada to Argentina (Sauer 1950b). Their common name, pigweed, may have comes from its use as fodder for pigs. Pigweed plants are commonly considered to be weeds by farmers and gardeners because they thrive in disturbed soils.
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Q: Is waterhemp toxic?
A: About Waterhemp: This weed is poisonous for cattle, horses, sheep and goats when ingested.
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Q: What amaranth is not edible?
A: Nearly all amaranths are edible, including ‘love-lies-bleeding’ and even the common roadside weedy forms. But those sold as edible varieties are selected for their good seed production and especially tasty leaves.
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Q: Is red amaranth invasive?
A: Although waterhemp, pigweed, and Palmer amaranth are problematic weed species of Amaranthus, the ornamental and edible types of amaranth are generally not considered invasive in gardens.
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About the author

Samuel is a gardening professional and enthusiast who has spent over 20 years advising homeowners and farm owners on weed identification, prevention and removal. He has an undergraduate degree in plant and soil science from Michigan State University.