<b>HRAC Group 22</b> <font size='2'> (Legacy D) </font> resistant Landoltia punctata from United States, Florida

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

HRAC GROUP 22 (LEGACY D) RESISTANT DOTTED DUCKWEED
(Landoltia punctata)

PS I Electron Diversion HRAC Group 22 (Legacy D)

United States, Florida

INTRODUCTION		DOTTED DUCKWEED
Dotted Duckweed (Landoltia punctata) is a dicot weed in the Lemnaceae family. In Florida this weed first evolved resistance to Group 22 (Legacy D) herbicides in 2001 and infests Aquatic. Group 22 (Legacy D) herbicides are known as PS I Electron Diversion (PSI Electron Diversion ). Research has shown that these particular biotypes are resistant to diquat, and paraquat and they may be cross-resistant to other Group 22 (Legacy D) 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 May 24, 2005 )
Common Name	Dotted Duckweed
Species	Landoltia punctata
Group	PS I Electron Diversion HRAC Group 22 (Legacy D)
Herbicides	diquat, and paraquat
Location	United States, Florida
Year	2001
Situation(s)	Aquatic
Contributors - (Alphabetically)	Tyler Koschnick
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ACADEMIC ASPECTS

Confirmation Tests

Laboratory trials comparing a known susceptible Dotted Duckweed biotype with this Dotted Duckweed 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 22 resistant Dotted Duckweed 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 22 (Legacy D) resistant Dotted Duckweed from Florida please update the database.

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CONTRIBUTING WEED SCIENTISTS

TYLER KOSCHNICK

Visiting Assistant Professor University Of Florida Agronomy 915 W State St Gainesville, 32653, Florida United States Email Tyler Koschnick

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Florida have been instrumental in providing you this information. Particular thanks is given to Tyler Koschnick for providing detailed information.

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Herbicide Resistant Dotted Duckweed Globally
(Landoltia punctata)

Country

FirstYear

Situation

Active Ingredients

Site of Action

United States (Florida)

2001

Aquatic

diquat, and paraquat

PS I Electron Diversion ( HRAC Group 22 (Legacy D)

Literature about Similar Cases

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Koschnick, T. J. ; Haller, W. T. ; Glasgow, L.. 2006. Documentation of landoltia (Landoltia punctata) resistance to diquat. Weed Science 54 : 615 - 619.

Landoltia was collected and cultured from a canal in Lake County, Florida, USA, where diquat was used repeatedly during the past 20-30 years for duckweed (Lemna sp.) control. Recent applications of diquat failed to provide adequate control of duckweed, and a new commercial formulation of diquat was suspected. The new formulation was not the cause of reduced efficacy. Static exposures (48 h) to various concentrations of diquat were used to compare the susceptibility of the Lake County landoltia accession to one never exposed to diquat. These static tests indicated that landoltia, from a population with no prior history of herbicide treatment, was extremely susceptible to diquat. The accession from Lake County had developed resistance to diquat, and was also cross resistant to paraquat. The resistance factor was 50 for diquat and 29 for paraquat. The Lake County accession also exhibited reduced ion leakage after diquat exposure under light and dark conditions. This suggests the resistance mechanism to the bipyridylium herbicides in landoltia is independent of photosynthetic electron transport. This research documents the first aquatic plant species that has developed resistance to the bipyridylium herbicides..

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Heap, I. The International Herbicide-Resistant Weed Database. Online. Sunday, October 4, 2026. Available at www.weedscience.org

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