Ladysthumb (Polygonum persicaria) is a dicot weed in the Polygonaceae family.  In New Zealand this weed first evolved resistance to Group C1/5 herbicides in 1980 and infests Corn (maize).   Group C1/5 herbicides are known as Photosystem II inhibitors (Inhibition of photosynthesis at photosystem II).  Research has shown that these particular biotypes are resistant to atrazine and they may be cross-resistant to other Group C1/5 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 Sep 15, 2000 )

Common NameLadysthumb
SpeciesPolygonum persicaria
GroupPhotosystem II inhibitors (C1/5)
LocationNew Zealand
Situation(s)Corn (maize)
Contributors - (Alphabetically)Anis Rahman 
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Anis Rahman
Waikato, Bay of Plenty, Gisborne.

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Anis Rahman
Is being controlled with alternative pre-emergence herbicides. Where necessary post-emergence herbicide is used for its control.

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Confirmation Tests

Field, and Greenhouse trials comparing a known susceptible Ladysthumb biotype with this Ladysthumb 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 Group C1/5 resistant Ladysthumb 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

Triazine resistant weeds often exhibit a lower relative fitness when compared to susceptible biotypes.  The most common mutation conferring triazine resistance (Ser 264 to Gly mutation of the psbA gene) also causes a reduction in CO2 fixation, quantum yield, and seed and biomass production.  There is no record in this database referring specifically to fitness studies on Group C1/5 resistant Ladysthumb from New Zealand.
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Ruakura Agricultural Centre
Ag. Research
3205 College Ave
New Zealand
Email Anis Rahman


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in New Zealand have been instrumental in providing you this information. Particular thanks is given to Anis Rahman for providing detailed information.
Herbicide Resistant Ladysthumb Globally
(Polygonum persicaria)
Herbicide Resistant Ladysthumb Globally
(Polygonum persicaria)
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Herbicide Resistant Ladysthumb Globally
(Polygonum persicaria)
#CountryFirstYearSituationActive IngredientsSite of Action
1 Czech RepublicCzech Republic 1989 Railways atrazine, cyanazine, lenacil, prometryn, simazine, and terbutryn 12 Photosystem II inhibitors (C1/5)
136Polygonum persicariaLadysthumb82
2 FranceFrance 1980 Corn (maize), and Cropland atrazine 17 Photosystem II inhibitors (C1/5)
136Polygonum persicariaLadysthumb467
3 New ZealandNew Zealand 1980 Corn (maize) atrazine 30 Photosystem II inhibitors (C1/5)
136Polygonum persicariaLadysthumb157
4 NorwayNorway 2009 Spring Barley, and Wheat tribenuron-methyl 31 ALS inhibitors (B/2)
136Polygonum persicariaLadysthumb10977
5 United States (Michigan) United StatesMichigan2001 Blueberries atrazine, and simazine 45 Photosystem II inhibitors (C1/5)
136Polygonum persicariaLadysthumb5178
Literature about Similar Cases

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PERMISSION MUST BE OBTAINED FIRST if you intend to base a significant portion of a scientific paper on data derived from this site. Citation:
Heap, I.  The International Herbicide-Resistant Weed Database.  Online.  Wednesday, August 12, 2020 .  Available Copyright © 1993- 2020 All rights reserved. Fair use of this material is encouraged. Proper citation is requested.