Amaranthus tuberculatus

Taxobox
name = "Amaranthus tuberculatus"

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image_width = 240px
image_caption =
regnum = Plantae
divisio = Magnoliophyta
classis = Magnoliopsida
ordo = Caryophyllales
familia = Amaranthaceae
genus = "Amaranthus"
species = "A. tuberculatus"
binomial = "Amaranthus tuberculatus"
binomial_authority = (Moq.) J.D.Sauer

"Amaranthus tuberculatus", commonly known as tall waterhemp or roughfruit amaranth, is a species of flowering plant. It is a summer annual broadleaf with a germination period that lasts several monthscite paper | first = Stephen| last = Gower | coauthors= Chad Lee| title = Tall Waterhemp Management in Corn and Soybeans | publisher = Center for Integrated Plant Systems, Michigan State University | date = November 2001| url = http://www.pestid.msu.edu/profiles/TallWaterhemp.PDF| format = pdf | accessdate = 2007-12-26] Tall waterhemp has been reported as a weed in 40 of 50 U.S. Statescite web |url=http://plants.usda.gov/java/profile?symbol=AMTU/symposium.shtml |title= "Amaranthus tuberculatus" (Moq.) Sauer |work=PLANTS Database|publisher=United States Department of Agriculture | accessdate = 2007-12-26]

Morphology

A distinguishing characteristic of tall waterhemp that sets it apart from similar members of the genus Amaranthus is the lack of hair on its stems and leaves. This characteristic gives the plant a bright, glossy appearance. The leaves of tall waterhemp tend to be long and narrow.

The stem is typically erect and slender and can be up to three feet long. The color of the stem is green or red. Tall waterhemp is a dioecious plant. The seedhead branches in the female are numerous, short, and smooth. The male seedhead branches are fewer, longer, and more slender than those of the female.

The species has terminal spike inflorescences and very short bracts with simple to highly branched flowers. Seed produced is reddish to black in colour and less than 1/32 inch in diameter.cite web| first = Jim| last = Stritzke| title = Tall Waterhemp|work= Oklahama Alfalfa| publisher = Oklahoma State University| url = http://alfalfa.okstate.edu/weeds/pigweed/twaterhemp.htm| accessdate = 2007-12-26]

Geographic distribution

Tall waterhemp is native to the United States and is believed to have originally had a range north of Missouri and Tennessee to the Great Lakes. It is now found in 40 states.

Habitat

Tall waterhemp predominatly grows in wet habitats, such as ponds, marshes, lakes, creeks, and other riparian zones. It also thrives along roadways and railroads as well as agricultural fields. It can grow in a variety of climates, as evidenced by its widespread range.

Growth and development

Tall waterhemp is a summer annual that produces a large amountquantify|date=August 2008 of very smallquantify|date=August 2008 seed. It is considered an r-strategist. Emergence can span several months and often occurs later in the season than other annual weeds, allowing the weed to evade typical weed control strategies such as herbicide application and tillage. One study observed 80% emergence not occurring until ten weeks after the initial emergence [Weekly emergence of waterhemp and giant ragweed in Ames, IA. 2000. Sandell, Buhler and Hartzler, Iowa State University] . Extreme temperatures have little affect on seed viability. Germination occurs typically after soil temperature alternation, as this is required to break seed dormancy [Leon RG, Knapp AD, Owen MDK (2004) Effect of temperature on the germination of common waterhemp (Amaranthus tuberculatus), giant foxtail (Setaria faberi), and velvetleaf (Abutilon theophrasti). Weed Science: Vol. 52, No. 1 pp. 67–73] . Waterhemp has been found to germinate in a wide range of soil and temperature conditions.. It has been found to germinate 17 years after seed set [Burnside, O.C., R.G. Wilson, S.Weisberg and K.G. Hubbard. Seed longevity of 41 weed species buried 17 years in eastern and western Nebraska. Weed Sci. 44:74-86.]

While tall waterhemp cannot self-pollinate, due to having separate male and female plants, it does not require any vectors for pollinationcite web|url=http://web.archive.org/web/20061018184807/http://www.weeds.iastate.edu/mgmt/2003/symposium.shtml |title= Waterhemp - The Perfect Weed? |work=Weed Science|publisher=Iowa State University | accessdate = 2007-12-26] This allows for wind pollination over large distances, generating a large amount of genetic diversity. Another factor contributing to genetic diversity is the large amount of seed produced. Tall waterhemp in competition with soybean has been reported to produce from between 300,000 to 5,000,000 seed per plant [Hartzler, R.G., B.A. Battles and D. Refsell. 2004. Effect of common waterhemp emergence date on growth and fecundity in Glycine max. Weed Sci. 52.] . Tall waterhemp also has a rapid growth rate, 50%-70% greater than other annual weeds [Horak, M.J. and T.M. Loughin. 2000. Growth analysis of four Amaranthus species. Weed Sci. 48:347-355.] .

Interspecific hybridization

Interspecific hybrids of tall waterhemp and "Amaranthus hybridus" have been observed in experimental fields [Trucco, F., M.R. Jeschke, A.L. Rayburn, and P.J. Tranel. 2005. Amararthus hybrids can be pollinated frequently by A. tuberculatus under field conditions. Heredity 94:64–70.] but have not been observed in agronomic fields [Rayburn, A. Lane, McCloskey, R., Tatum, Tatiana C., Bollero, German A., Jeschke, Mark R., Tranel, Patrick J. Genome Size Analysis of Weedy Amaranthus Species. Crop Sci 2005 45: 2557-2562] .

Agricultural impacts and control

In North America, tall waterhemp is considered a major weed of agricultural fields and other disturbed habitats.cite web |url=http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=242415651 |title= "Amaranthus tuberculatus" |work=Flora of North America Vol. 4 |publisher=www.eFloras.org ] The Southern Weed Science Society includes tall waterhemp on their list of weed species [Southern Weed Science Society. 1998. Weeds of the United States and Canada. CD-ROM. Southern Weed Science Society. Champaign, Illinois] . However, it is not listed on the federal noxious weed list or any state lists in the United States.cite web |url=http://plants.usda.gov/java/noxComposite|title= Federal and State Noxious Weeds|work=PLANTS Database|publisher=United States Department of Agriculture | accessdate = 2007-12-26] In Europe and other continents where the species has been introduced, naturalization is an infrequent occurrence.

Because of the long germination window for tall waterhemp, a single herbicide application is unlikely to be an effective control strategy. Michigan State University Extension recommends a preemergence application followed by one or more postemergence applications. Tall waterhemp have been reported resistant to acetolactate synthase inhibiting (ALS) herbicides and the triazines, with some individual weeds being resistant to both herbicides groups. Resistance to acifluorfen and other diphenyl ether herbicides has been reported.According to Bob Hartzler of Iowa State University, the most effective control of tall waterhemp is achieved by cultural practices that promote growth of the desired vegetation.

References