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Title: Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) Spreads in the Southern United States (U.S.)

Author
item NICHOLS, R - Cotton, Inc
item BOND, J - Mississippi State University
item CULPEPPER, A - University Of Georgia
item DODDS, D - Mississippi State University
item NANDULA, V - Mississippi State University
item MAIN, C - University Of Tennessee
item MARSHALL, M - Clemson University
item MUELLER, T - University Of Tennessee
item NORSWORTHY, J - University Of Arkansas
item Price, Andrew
item PATTERSON, M - Auburn University
item SCOTT, R - University Of Arkansas
item SMITH, K - University Of Arkansas
item STECKEL, L - University Of Tennessee
item STEPHENSON, D - Louisiana State University
item WRIGHT, D - University Of Florida
item YORK, A - North Carolina State University

Submitted to: Popular Publication
Publication Type: Popular Publication
Publication Acceptance Date: 5/12/2009
Publication Date: 5/12/2009
Citation: Nichols, R.L., Bond, J., Culpepper, A.S., Dodds, D., Nandula, V., Main, C.L., Marshall, M.W., Mueller, T.C., Norsworthy, J.K., Price, A.J., Patterson, M., Scott, R.C., Smith, K.L., Steckel, L.E., Stephenson, D., Wright, D., York, A.C. 2009. Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) Spreads in the Southern United States (U.S.). Resistant Pest Management Newsletter.

Interpretive Summary: Glyphosate is an exceptionally broad-spectrum herbicide that was first registered for use in 1974. Glyphosate is used mainly in conjunction with transgenic, glyphosate-resistant soybean, canola, cotton, and corn cultivars, and has become the most widely-used herbicide in the world. Since the introduction of transgenic glyphosate-resistant crops, fifteen weed species throughout the world have developed resistance to glyphosate. One of the most serious of the glyphosate-resistant weeds is Palmer amaranth because of its wide distribution through the southern and southwestern U.S., its rapid growth, its ability to compete with crops, and its very high reproductive potential. In 2008, researchers reported that 49 counties had at least one glyphosate resistant population. In 2009, 93 counties have confirmed populations. Moreover, numerous other populations are pending confirmation, including populations in Florida and Louisiana that are in counties that are not contiguous with currently confirmed counties. Given the rate of spread observed since the initial confirmation of resistance, it is probable that Palmer amaranth will be resistant to glyphosate throughout its range in the not too distant future. Such an occurrence will likely result in crop yield and quality losses, increased herbicide costs, and the possibility of changing tillage and cropping systems.

Technical Abstract: Glyphosate (N-phosphonomethyl glycine) is an exceptionally broad-spectrum herbicide that was first registered for use in 1974. Glyphosate is used mainly in conjunction with transgenic, glyphosate-resistant soybean, canola (Brassica napus), cotton (Gossypium hirsutum), and corn (Zea mays) cultivars, and has become the most widely-used herbicide in the world. Since the introduction of transgenic glyphosate-resistant crops, fifteen weed species throughout the world have developed resistance to glyphosate. One of the most serious of the glyphosate-resistant weeds is Palmer amaranth because of its wide distribution through the southern and southwestern U.S., its rapid growth, its ability to compete with crops, and its very high reproductive potential. In 2008, researchers reported that 49 counties had at least one glyphosate resistant population. In 2009, 93 counties have confirmed populations. Moreover, numerous other populations are pending confirmation, including populations in Florida and Louisiana that are in counties that are not contiguous with currently confirmed counties. Given the rate of spread observed since the initial confirmation of resistance, it is probable that Palmer amaranth will be resistant to glyphosate throughout its range in the not too distant future. Such an occurrence will likely result in crop yield and quality losses, increased herbicide costs, and the possibility of changing tillage and cropping systems.