International Survey of Herbicide-Resistant Weeds

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(Amaranthus spinosus)

EPSP synthase inhibitors (G/9)

United States, Mississippi
Spiny Amaranth (Amaranthus spinosus) is a dicot weed in the Amaranthaceae family.  In Mississippi this weed first evolved resistance to Group G/9 herbicides in 2012 and infests Cotton.   Group G/9 herbicides are known as EPSP synthase inhibitors (Inhibition of EPSP synthase).  Research has shown that these particular biotypes are resistant to glyphosate and they may be cross-resistant to other Group G/9 herbicides.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

If we do not have a picture for this weed, or you can provide a better picture (scan, digital camera etc) please please e-mail it to us.

QUIK STATS (last updated Aug 12, 2012 )

Common NameSpiny Amaranth
SpeciesAmaranthus spinosus
GroupEPSP synthase inhibitors (G/9)
LocationUnited States, Mississippi
Contributors - (Alphabetically)Vijay Nandula 
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Confirmation Tests

Greenhouse trials comparing a known susceptible Spiny Amaranth biotype with this Spiny Amaranth biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetic studies on Group G/9 resistant Spiny Amaranth have not been reported to the site.  There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature
Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database.  If you know anything about the mechanism of resistance for this biotype then please update the database.
Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes.  If you have any information pertaining to the fitness of Group G/9 resistant Spiny Amaranth from Mississippi please update the database.
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Research Plant Physiologist
Crop Production Systems Research Unit
141 Experiment Station Road
Stoneville, 38776, Mississippi
United States
Email Vijay Nandula
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Mississippi have been instrumental in providing you this information. Particular thanks is given to Vijay Nandula for providing detailed information.
Herbicide Resistant Spiny Amaranth Globally
(Amaranthus spinosus)
Herbicide Resistant Spiny Amaranth Globally
(Amaranthus spinosus)
Drag a column header and drop it here to group by that column
Herbicide Resistant Spiny Amaranth Globally
(Amaranthus spinosus)
#CountryFirstYearSituationActive IngredientsSite of Action
1 United States (Mississippi) United StatesMississippi2012 Cotton glyphosate 45 EPSP synthase inhibitors (G/9)
278Amaranthus spinosusSpiny Amaranth5682
2 United States (Mississippi) United StatesMississippi2013 Cotton, and Soybean imazethapyr, nicosulfuron, pyrithiobac-sodium, and trifloxysulfuron-sodium 45 ALS inhibitors (B/2)
278Amaranthus spinosusSpiny Amaranth16081
Literature about Similar Cases

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