International Survey of Herbicide-Resistant Weeds

Countries Weeds Herbicides Mutations Graphs References Researchers
(Digitaria ischaemum)

Auxin Mimics HRAC Group 4 (Legacy O)

United States, California
Smooth Crabgrass (Digitaria ischaemum) is a monocot weed in the Poaceae family.  In California this weed first evolved resistance to Group 4 (Legacy O) herbicides in 2002 and infests Rice.   Group 4 (Legacy O) herbicides are known as Auxin Mimics (Auxin Mimics ).  Research has shown that these particular biotypes are resistant to quinclorac and they may be cross-resistant to other Group 4 (Legacy O) 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 Jan 14, 2003 )

Common NameSmooth Crabgrass
SpeciesDigitaria ischaemum
GroupAuxin Mimics HRAC Group 4 (Legacy O)
LocationUnited States, California
Contributors - (Alphabetically)Albert Fischer 
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Confirmation Tests

Field, and Greenhouse trials comparing a known susceptible Smooth Crabgrass biotype with this Smooth Crabgrass 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 4 resistant Smooth Crabgrass 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 4 (Legacy O) resistant Smooth Crabgrass from California please update the database.
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University Of California
Department of Plant Sciences
Weed Ecophysiology
Mail Stop #4 279/279A Robbins Hall
Davis, 95616, California
United States
Email Albert Fischer
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in California have been instrumental in providing you this information. Particular thanks is given to Albert Fischer for providing detailed information.
Herbicide Resistant Smooth Crabgrass Globally
(Digitaria ischaemum)
Herbicide Resistant Smooth Crabgrass Globally
(Digitaria ischaemum)
Drag a column header and drop it here to group by that column
Herbicide Resistant Smooth Crabgrass Globally
(Digitaria ischaemum)
#CountryFirstYearSituationActive IngredientsSite of Action
1 United States (New Jersey) United StatesNew Jersey1996 Turf fenoxaprop-ethyl 45 Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
177Digitaria ischaemumSmooth Crabgrass556
2 United States (California) United StatesCalifornia2002 Rice quinclorac 45 Auxin Mimics ( HRAC Group 4 (Legacy O)
177Digitaria ischaemumSmooth Crabgrass5134
Literature about Similar Cases

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