<b>HRAC Group 4</b> <font size='2'> (Legacy O) </font> resistant Galeopsis tetrahit from Canada, Alberta

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

HRAC GROUP 4 (LEGACY O) RESISTANT COMMON HEMPNETTLE
(Galeopsis tetrahit)

Auxin Mimics HRAC Group 4 (Legacy O)

Canada, Alberta

INTRODUCTION		COMMON HEMPNETTLE
Common Hempnettle (Galeopsis tetrahit) is a dicot weed in the Lamiaceae family. In Alberta this weed first evolved resistance to Group 4 (Legacy O) herbicides in 1998 and infests Cereals, Cropland, Spring Barley, and Wheat. Group 4 (Legacy O) herbicides are known as Auxin Mimics (Auxin Mimics ). Research has shown that these particular biotypes are resistant to dicamba, fluroxypyr, and MCPA 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.

QUIK STATS (last updated Feb 28, 2005 )
Common Name	Common Hempnettle
Species	Galeopsis tetrahit
Group	Auxin Mimics HRAC Group 4 (Legacy O)
Herbicides	dicamba, fluroxypyr, and MCPA
Location	Canada, Alberta
Year	1998
Situation(s)	Cereals, Cropland, Spring Barley, and Wheat
Contributors - (Alphabetically)	Lyle Friesen, Chris Hall, John O'Donovan, and Tsafrir Weinberg
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NOTES ABOUT THIS BIOTYPE

AREAS FOUND

John O'Donovan

Lacombe, Alberta, Canada

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ACADEMIC ASPECTS

Confirmation Tests

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

Genetics

Genetic studies on HRAC Group 4 resistant Common Hempnettle 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 Common Hempnettle from Alberta please update the database.

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CONTRIBUTING WEED SCIENTISTS

LYLE FRIESEN

University Of Manitoba Agriculture Bldg Rua Hugo Cabral 1065 Apto 301 Winnipeg, R3T 2N2, Manitoba Canada Email Lyle Friesen

CHRIS HALL

University Of Guelph Department Of Environmental Biology Dept. Producao Vegetal Caixa Postal 09, Av. Padua Dias 11 Guelph, N1G 2W1, Ontario Canada Email Chris Hall

JOHN O'DONOVAN

Agriculture And Agri-Food Canada Department Of Environmental Biology Universidad Nacional De Mar Del Plata Ruta Nacional 226, Km 73.5, Beaverlodge, T0H 0C0, Alberta Canada Email John O'Donovan

TSAFRIR WEINBERG

Ph. D. Student University Of Guelph Depart. Of Environmental Biology 108 Waters Hall Guelph, N1G 2W1, Ontario Canada Email Tsafrir Weinberg

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Alberta have been instrumental in providing you this information. Particular thanks is given to Lyle Friesen, Chris Hall, John O'Donovan, and Tsafrir Weinberg for providing detailed information.

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Herbicide Resistant Common Hempnettle Globally
(Galeopsis tetrahit)

Country

FirstYear

Situation

Active Ingredients

Site of Action

Canada (Manitoba)

1995

Cereals, and Wheat

metsulfuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Canada (Alberta)

1998

Cereals, Cropland, Spring Barley, and Wheat

dicamba, fluroxypyr, and MCPA

Auxin Mimics ( HRAC Group 4 (Legacy O)

Canada (Alberta)

2006

Cereals

thifensulfuron-methyl, and tribenuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Literature about Similar Cases

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Weinberg, T. ; Stephenson, G. R. ; McLean, M. D. ; Hall, J. C.. 2006. MCPA (4-chloro-2-ethylphenoxyacetate) resistance in hemp-nettle (Galeopsis tetrahit L.). Journal of Agricultural and Food Chemistry 54 : 9126 - 9134.

The physiological basis for MCPA resistance in a hemp-nettle (Galeopsis tetrahit L.) biotype, obtained from a MCPA-resistant field population, was investigated. Dose-response studies revealed that the resistance factor for MCPA, based on GR₅₀ comparisons of total dry weight of resistant (R) and susceptible (S) plants, was 3.3. Resistance factors for fluroxypyr, dicamba, 2,4-D, glyphosate, and chlorsulfuron were 8.2, 1.7, 1.6, 0.7, and 0.6, respectively. MCPA resistance was not due to differences in absorption, because both R and S biotypes absorbed 54% of applied [¹⁴C]MCPA 72 h after treatment. However, R plants exported less (45 vs 58% S) recovered ¹⁴C out of treated leaves to the apical meristem (6 vs 13% S) and root (32 vs 38% S). In both biotypes, approximately 20% of the ¹⁴C recovered in planta was detected as MCPA metabolites. However, less of the ¹⁴C recovered in the roots of R plants was MCPA. Therefore, two different mechanisms protect R hemp-nettle from MCPA phytotoxicity: a lower rate of MCPA translocation and a higher rate of MCPA metabolism in the roots. In support of these results, genetic studies indicated that the inheritance of MCPA resistance is governed by at least two nuclear genes with additive effects..

Petersen, E. F.. 2004. How does DuPont deals with the resistance challenge?. DJF Rapport, Markbrug : 185 - 196.

DuPont was the first and is still the largest producer of sulfonylurea herbicides. This role makes it necessary to participate in developing resistance strategies so that the products can be used for effective weed control. Part of the strategy is to develop methods for analysing resistance. Three methods for the analysis of herbicide resistance are used by DuPont: (1) cultivation of the plants in the greenhouse (this takes several weeks before results are obtained), (2) cultivation of seeds and whole plants on agar in a climate chamber (this takes only 2-3 weeks and can be used for calculating the resistance level in a biotype), and (3) in vivo method used for determining the resistance type. The most important parts of the strategies are the recommendations, which include: change of mode of action in the rotation, use of products with short persistence, and total weed control after harvest followed by ploughing/harrowing. To secure the future control of black grass [Alopecurus myosuroides], it is very important to follow the resistance strategy, as this weed quickly develops resistance against new herbicides. In Denmark, sulfonylurea herbicides are widely used; thus, resistance cases are most likely prevalent, such as in chickweed [Stellaria media] and hemp nettle [Galeopsis tetrahit]. This incidence is due to the adoption of herbicide mixtures by farmers instead of the application of sole sulfonylurea herbicide..

Thomas, A. G. ; Doohan, D. J. ; McCully, K. V.. 1994. Weed survey of spring cereals in New Brunswick. Phytoprotection 75 : 113 - 124.

During 1986 and 1987, a weed survey of 187 New Brunswick cereal fields was conducted. A total of 76 species were identified, of which 40 were considered agronomically important. About 50% of the species were perennial. Hemp-nettle (Galeopsis tetrahit), quack grass (Agropyron repens [Elymus repens]), sheep sorrel (Rumex acetosella), ox-eye daisy (Chrysanthemum leucanthemum [Leucanthemum vulgare]), corn spury (Spergula arvensis) and chickweed (Stellaria media) had the highest relative abundance values. Quack grass and hemp-nettle had the highest densities at 8.0 and 7.1 plants m^-2, respectively. The highest weed density (103 plants m^-2) was found in oats (Avena sativa) grown after a forage crop. The lowest density (24 plants m^-2) was found in wheat (Triticum aestivum) grown after potatoes (Solanum tuberosum). Most of the abundant species were tolerant to MCPA, the most commonly used herbicide. It was concluded that farmers could make major improvements in cereal weed control by choosing a herbicide that would control species tolerant to MCPA or 2,4-D, and using preplant or postharvest weed control to minimize the impact of perennial weeds..

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