International Survey of Herbicide-Resistant Weeds

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(Picris hieracioides)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Hawkweed Oxtongue (Picris hieracioides) is a dicot weed in the Asteraceae family.  In Russia this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2000 and infests Wheat.   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 amidosulfuron, chlorsulfuron, triasulfuron, and tribenuron-methyl 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 Mar 06, 2004 )

Common NameHawkweed Oxtongue
SpeciesPicris hieracioides
GroupInhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicidesamidosulfuron, chlorsulfuron, triasulfuron, and tribenuron-methyl
Contributors - (Alphabetically)Peter Solymosi 
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Solymosi, P.; Nagy, P. 2000. Sulfonylurea resistance in Picris hieracioides L. Növényvédelem 2000 Vol. 36 No. 12 pp. 619-624
A keserűgyökér (Picris hieracioides L.) taxonómiailag is azonosítható szulfonilkarbamidellenálló biotípusának jellemzése.

We have found a sulfonylurea resistant Picris hieracioides biotype in Russia. This is a new case of sulfonylurea resistance. The degree of resistance varies with the biotype and herbicide. For chlorsulfuron, triasulfuron, tribenuron-methyl and amidosulfuron, the herbicide concentration required to reduce enzyme activity 50% (I50) was 6 to 22-fold greater using ALS [acetolactate synthase] isolated from the resistant biotype compared to ALS from the susceptible biotype. The imidazolinone herbicide imazapyr was less inhibitory (1.4-fold) to resistant P. hieracioides ALS. Lontrel 300 [clopyralid] (0.5 l/ha) and Mustang [florasulam + 2,4-D] (0.6 l/ha) herbicides were effective against the sulfonylurea resistant biotype of P. hieracioides.

Hungarian Academy of Sciences, 1245 Budapest, P.O. Box 1000, Hungary.

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Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Hawkweed Oxtongue biotype with this Hawkweed Oxtongue 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 Hawkweed Oxtongue 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 Hawkweed Oxtongue from Russia please update the database.
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Hungarian Academy Of Sciences
Dept of Horticulture
164 Plant Science Bldg,
Budapest, H-1525


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Russia have been instrumental in providing you this information. Particular thanks is given to Peter Solymosi for providing detailed information.
Herbicide Resistant Hawkweed Oxtongue Globally
(Picris hieracioides)
Herbicide Resistant Hawkweed Oxtongue Globally
(Picris hieracioides)
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Herbicide Resistant Hawkweed Oxtongue Globally
(Picris hieracioides)
#CountryFirstYearSituationActive IngredientsSite of Action
1 RussiaRussia 2000 Wheat amidosulfuron, chlorsulfuron, triasulfuron, and tribenuron-methyl 65 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
314Picris hieracioidesHawkweed Oxtongue7894
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