International Survey of Herbicide-Resistant Weeds

Countries Weeds Herbicides Mutations Graphs References Researchers
(Polygonum pensylvanicum)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

United States, Arkansas
Pennsylvania Smartweed (Polygonum pensylvanicum) is a dicot weed in the Polygonaceae family.  In Arkansas this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2020 and infests Rice.   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 bispyribac-sodium, halosulfuron-methyl, and prosulfuron 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.

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 30, 2021 )

Common NamePennsylvania Smartweed
SpeciesPolygonum pensylvanicum
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicidesbispyribac-sodium, halosulfuron-methyl, and prosulfuron
LocationUnited States, Arkansas
Contributors - (Alphabetically)Tom Barber, Thomas Butts, and Jason Norsworthy 
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Confirmation Tests

Greenhouse trials comparing a known susceptible Pennsylvania Smartweed biotype with this Pennsylvania Smartweed 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 Pennsylvania Smartweed 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 Pennsylvania Smartweed from Arkansas please update the database.
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Associate Prof-Weed Scientist
University of Arkansas
Crop, Soil & Environmental Science
102 NE Front St Suite 2
Lonoke, 72806, Arkansas
United States
Email Tom Barber
Assistant Professor, Extension Weed Scientist
University of Arkansas System Division of Agriculture
Crop, Soil
and Environmental Sciences
2001 Hwy 70 E
Lonoke, 72086, Arkansas
United States
Email Thomas Butts
Web   : Web Site Link
University Of Arkansas
Department Of Crop
Soil, And Environmental Sciences
1366 West Altheimer Drive
Williams Hall
Fayetteville, 72704, Arkansas
United States
Email Jason Norsworthy
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Arkansas have been instrumental in providing you this information. Particular thanks is given to Tom Barber, Thomas Butts, and Jason Norsworthy for providing detailed information.
Herbicide Resistant Pennsylvania Smartweed Globally
(Polygonum pensylvanicum)
Herbicide Resistant Pennsylvania Smartweed Globally
(Polygonum pensylvanicum)
Drag a column header and drop it here to group by that column
Herbicide Resistant Pennsylvania Smartweed Globally
(Polygonum pensylvanicum)
#CountryFirstYearSituationActive IngredientsSite of Action
1 United States (Iowa) United StatesIowa1990 Corn (maize) atrazine 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
135Polygonum pensylvanicumPennsylvania Smartweed240
2 United States (Arkansas) United StatesArkansas2020 Rice bispyribac-sodium, halosulfuron-methyl, and prosulfuron 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
135Polygonum pensylvanicumPennsylvania Smartweed20230
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