International Survey of Herbicide-Resistant Weeds

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(Sida spinosa)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

United States, Georgia
Prickly Sida (Sida spinosa) is a dicot weed in the Malvaceae family.  In Georgia this weed first evolved resistance to Group 2 (Legacy B) herbicides in 1993 and infests Cropland.   Group 2 (Legacy B) herbicides are known as Inhibition of Acetolactate Synthase (Inhibition of Acetolactate Synthase ).  Research has shown that these particular biotypes are resistant to imazaquin and they may be cross-resistant to other Group 2 (Legacy B) 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.

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QUIK STATS (last updated Nov 21, 2000 )

Common NamePrickly Sida
SpeciesSida spinosa
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
LocationUnited States, Georgia
Contributors - (Alphabetically)David Bridges 
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David Bridges

ALS-Inhibitor Resistance Working Group (AIRWG) Meeting Minutes

The ALS/AHAS-Inhibitor Herbicide Resistance Working Group (AIRWG) Meeting held in St. Louis, Missouri, on September 15th and 16th, 1993, was attended by 12 academics and 17 technical representatives from industry. The first day of the meeting included reports from academics followed by brainstorming sessions on how to deal with short- and long term resistance management.

Academic Session, September 15, 1993

Reports of resistant weeds in Georgia

  • ALS-inhibitor resistant prickly sida (Sida spinosa); also known as teaweed
  • DNA-resistant goosegrass (Eleusine indica), especially on golf courses; may also be less sensitive to dithiopyr
  • ACCase-inhibitor resistant annual ryegrass (Lolium sp.) and Johnsongrass (Sorghum halepense); ryegrass was selected on the GA Experimental Station
  • MSMA-resistant cocklebur (Xanthium strumarium); not spreading; only seen in continuous cotton
  • 2,4-D-resistant cocklebur claimed but NOT documented; Bridges et al. will investigate this winter
  • Paraquat-resistant coffee senna (Cassia occidentalis)
Greatest concern is the possibility of ALS-inhibitor resistance in Johnsongrass, especially in no-till corn where nicrosulfuron or primisulfuron are used every year. Believes that resistance is manageable on an on-farm basis, in contrast with western U.S. where large regions are infested with resistance. The RWM (resistance weed management) strategy proposed is to minimize exposure to selection pressure.

Perceived problems for RWM by academics:

  • Limiting the use (and therefore the selection pressure) of a product that is cheap, effective, and easy to use
  • Hard to implement the cleaning up of escapes with glyphosate
  • No action taken until problem occurs
  • Recommendations between university extension and industry are not the same - key to effective management is to have the same recommendations
Believes that all RWM strategies must reduce selection pressure: Are crop rotations useful? Are tank mixtures useful?

Dr. David Bridges, University of Georgia


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A letter from industry. August 22, 1995. American Cyanamid Company. Confirmation by Wendy Blair.

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Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Prickly Sida biotype with this Prickly Sida 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 HRAC Group 2 resistant Prickly Sida 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 2 (Legacy B) resistant Prickly Sida from Georgia please update the database.
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Abraham Baldwin Agricultural College
2802 Moore Highway
Tifton, 31793, Georgia
United States
Email David Bridges
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Georgia have been instrumental in providing you this information. Particular thanks is given to David Bridges for providing detailed information.
Herbicide Resistant Prickly Sida Globally
(Sida spinosa)
Herbicide Resistant Prickly Sida Globally
(Sida spinosa)
Drag a column header and drop it here to group by that column
Herbicide Resistant Prickly Sida Globally
(Sida spinosa)
#CountryFirstYearSituationActive IngredientsSite of Action
1 United States (Georgia) United StatesGeorgia1993 Cropland imazaquin 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
157Sida spinosaPrickly Sida325
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