International Survey of Herbicide-Resistant Weeds

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(Mazus pumilus)

PS I Electron Diversion HRAC Group 22 (Legacy D)

Japan, Oita
Japanese Mazus (Mazus pumilus) is a dicot weed in the Scrophulariaceae family.  In Japan this weed first evolved resistance to Group 22 (Legacy D) herbicides in 2006 and infests Gardens, Orchards, Roadsides, and Vegetables.   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 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.

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QUIK STATS (last updated Oct 21, 2014 )

Common NameJapanese Mazus
SpeciesMazus pumilus
GroupPS I Electron Diversion HRAC Group 22 (Legacy D)
LocationJapan, Oita
Situation(s)Gardens, Orchards, Roadsides, and Vegetables
Contributors - (Alphabetically)Satoshi Iwakami, Tohru Tominaga, and Akira Uchino 
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Tohru Tominaga
TSUJI K, HOSOKAWA M, MORITA S, MIURA R & TOMINAGA T (2013). Resistance to paraquat in Mazus pumilus. Weed Research 53, 176–182.
Mazus pumilus is an annual self-pollinating weed that is commonly found in arable land, vegetable gardens and roadsides. This weed harbours insects and pathogens that attack vegetables. The mechanism of resistance to paraquat of M. pumilus found in Ohita, Japan, was studied. Whole plant bioassays revealed that the resistant (R) biotypes were four to six times less susceptible than controls. Chlorophyll destruction of leaf discs by paraquat treatment in R biotypes was 4–20 times lower than those of susceptible (S) biotypes. Ferric reducing antioxidant power (FRAP) values in R biotypes were higher than those of S biotypes before and after paraquat treatments. The activity of superoxide dismutase (SOD) was also higher in R biotypes than those of S biotypes before and after treatment with paraquat, but the activities of ascorbate peroxidase (APX) and catalase (CAT) were not different between R and S biotypes. Change of ascorbate (AsA) contents before and after paraquat treatment was equivalent in both biotypes. These results indicate that the increased SOD activity and antioxidant capacity in R biotypes contribute to the resistance to paraquat of M. pumilus.

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Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Japanese Mazus biotype with this Japanese Mazus 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 22 resistant Japanese Mazus 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 Japanese Mazus from Japan please update the database.
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Weed Scientist
University of Tsukuba
Faculty of Life and Environmental Sciences
1-1-1 Tennoudai
Tsukuba, 305-8577, Ibaraki
Email Satoshi Iwakami
Kyoto University
Graduate School of Agriculture
Kyoto, 606-8502, Kyoto
Email Tohru Tominaga
Weed Scientist
NARO Agricultural Research Center
Graduate School of Agriculture
3-1-1 Kannondai
Tsukuba, 305-8666, Ibaraki
Email Akira Uchino


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Japan have been instrumental in providing you this information. Particular thanks is given to Satoshi Iwakami, Tohru Tominaga, and Akira Uchino for providing detailed information.
Herbicide Resistant Japanese Mazus Globally
(Mazus pumilus)
Herbicide Resistant Japanese Mazus Globally
(Mazus pumilus)
Drag a column header and drop it here to group by that column
Herbicide Resistant Japanese Mazus Globally
(Mazus pumilus)
#CountryFirstYearSituationActive IngredientsSite of Action
1 JapanJapan 2006 Gardens, Orchards, Roadsides, and Vegetables paraquat 25 PS I Electron Diversion ( HRAC Group 22 (Legacy D)
296Mazus pumilusJapanese Mazus7767
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