(Amaranthus blitum (ssp. oleraceus))

Photosystem II inhibitors (C1/5)

Switzerland, Valais
Livid Amaranth (Amaranthus blitum (ssp. oleraceus)) is a dicot weed in the Amaranthaceae family.  In Switzerland this weed first evolved resistance to Group C1/5 herbicides in 1978 and infests Grapes.   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 simazine 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 NameLivid Amaranth
SpeciesAmaranthus blitum (ssp. oleraceus)
GroupPhotosystem II inhibitors (C1/5)
LocationSwitzerland, Valais
Contributors - (Alphabetically)Jean Mayor 
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Confirmation Tests

Field, Greenhouse, and Laboratory trials comparing a known susceptible Livid Amaranth biotype with this Livid Amaranth 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 Livid Amaranth 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 Livid Amaranth from Switzerland.
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St. Federal De Recherches, Agronomy De Changins
Service De Malherbologie
Weed Mgmt Program Lead - Horticulture
120 Main St, PO Box 400
Nyon, CH-1260


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Switzerland have been instrumental in providing you this information. Particular thanks is given to Jean Mayor for providing detailed information.
Herbicide Resistant Livid Amaranth Globally
(Amaranthus blitum (ssp. oleraceus))
Herbicide Resistant Livid Amaranth Globally
(Amaranthus blitum (ssp. oleraceus))
Drag a column header and drop it here to group by that column
Herbicide Resistant Livid Amaranth Globally
(Amaranthus blitum (ssp. oleraceus))
#CountryFirstYearSituationActive IngredientsSite of Action
1 FranceFrance 1981 Corn (maize) atrazine 17 Photosystem II inhibitors (C1/5)
13Amaranthus blitum (ssp. oleraceus)Livid Amaranth454
2 MalaysiaMalaysia 1990 Vegetables paraquat 28 PSI Electron Diverter (D/22)
13Amaranthus blitum (ssp. oleraceus)Livid Amaranth137
3 SwitzerlandSwitzerland 1978 Grapes simazine 41 Photosystem II inhibitors (C1/5)
13Amaranthus blitum (ssp. oleraceus)Livid Amaranth196
4 United States (New Jersey) United StatesNew Jersey1993 Cabbages, Lettuce, and Onions imazethapyr 45 ALS inhibitors (B/2)
13Amaranthus blitum (ssp. oleraceus)Livid Amaranth1167
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.  Monday, March 1, 2021 .  Available Copyright © 1993- 2021 All rights reserved. Fair use of this material is encouraged. Proper citation is requested.