<b>HRAC Group 4</b> <font size='2'> (Legacy O) </font> resistant Digitaria ischaemum from United States, California

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

HRAC GROUP 4 (LEGACY O) RESISTANT SMOOTH CRABGRASS
(Digitaria ischaemum)

Auxin Mimics HRAC Group 4 (Legacy O)

United States, California

INTRODUCTION		SMOOTH CRABGRASS
Smooth Crabgrass (Digitaria ischaemum) is a monocot weed in the Poaceae family. In California this weed first evolved resistance to Group 4 (Legacy O) herbicides in 2002 and infests Rice. Group 4 (Legacy O) herbicides are known as Auxin Mimics (Auxin Mimics ). Research has shown that these particular biotypes are resistant to quinclorac 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 Jan 14, 2003 )
Common Name	Smooth Crabgrass
Species	Digitaria ischaemum
Group	Auxin Mimics HRAC Group 4 (Legacy O)
Herbicides	quinclorac
Location	United States, California
Year	2002
Situation(s)	Rice
Contributors - (Alphabetically)	Albert Fischer
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ACADEMIC ASPECTS

Confirmation Tests

Field, and Greenhouse trials comparing a known susceptible Smooth Crabgrass biotype with this Smooth Crabgrass 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 Smooth Crabgrass 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 Smooth Crabgrass from California please update the database.

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CONTRIBUTING WEED SCIENTISTS

ALBERT FISCHER

Professor University Of California Department of Plant Sciences Weed Ecophysiology Mail Stop #4 279/279A Robbins Hall Davis, 95616, California United States Email Albert Fischer Web : Web Site Link

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

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Herbicide Resistant Smooth Crabgrass Globally
(Digitaria ischaemum)

Country

FirstYear

Situation

Active Ingredients

Site of Action

United States (New Jersey)

1996

Turf

fenoxaprop-ethyl

Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)

United States (California)

2002

Rice

quinclorac

Auxin Mimics ( HRAC Group 4 (Legacy O)

Literature about Similar Cases

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Abdallah, I. ; Fischer, A. J. ; Elmore, C. L. ; Saltveit, M. E. ; Zaki, M.. 2006. Mechanism of resistance to quinclorac in smooth crabgrass (Digitaria ischaemum). Pesticide Biochemistry and Physiology 84 : 38 - 48.

The mechanism of resistance to quinclorac was investigated in a smooth crabgrass biotype [Digitaria ischaemum (Schreb. ex Schweig) Schreb. ex Muhl] from Tulare County, California. Quinclorac (8.96 kg a.i. ha^-1) had no effect (P=0.18) on the resistant (R) biotype, but reduced fresh weight of a susceptible (S) biotype by 93%. After treatment with 4.48 kg a.i. quinclorac ha^-1, the S biotype produced about three times more ethylene than the R biotype and accumulated cyanide in tissues. Similar amounts of endogenous cyanide resulting from treatment with KCN reproduced quinclorac phytotoxicity. Pre-treatment with the ACC synthase inhibitor AVG reduced quinclorac phytotoxicity by 37% and ethylene production by 89%. These data suggest a target site-based mechanism of resistance involving stimulation of ACC synthesis and accumulation of cyanide. Also, the R biotype had four times more β-cyanoalanine synthase activity than the S biotype, suggesting a higher ability to detoxify cyanide..

Dernoeden, P. H. ; Bigelow, C. A. ; Kaminski, J. E. ; Krouse, J. M.. 2003. Smooth crabgrass control in perennial ryegrass and creeping bentgrass tolerance to quinclorac. HortScience 38 : 607 - 612.

A 3-year (2000, 2001 and 2002) field study was conducted in Maryland, USA, to determine optimum rates and timings of quinclorac applications that provide consistent levels of effective crabgrass (Digitaria ischaemum) control and to assess creeping bentgrass (Agrostis stolonifera) quality responses to quinclorac. To evaluate crabgrass control, quinclorac was applied in early-, mid- and late-postemergence timings at various rates to a perennial ryegrass (Lolium perenne) turf. Similar treatments were applied to creeping bentgrass to determine if application timing and rate influenced the level and duration of discoloration. Quinclorac was applied alone or was tank-mixed with either urea (N at 6.1 kg/ha) or chelated iron (Fe) + nitrogen (N) (FeSO₄ at 1.1 kg/ha + N at 2.2 kg/ha) to determine if they would mask discoloration. Crabgrass control generally was more effective in the early- and mid-postemergence application timings. A single application of quinclorac (0.84 kg/ha) was effective where crabgrass levels were moderate, but sequential (i.e. multiple) applications were required where crabgrass levels were severe. The most consistent level of crabgrass control where weed pressure was severe occurred with three, sequential quinclorac (0.37 or 0.42 kg/ha) applications. Creeping bentgrass exhibited 2-11 weeks of unacceptable discoloration in response to sequential quinclorac applications. Chelated Fe + N was more effective than urea in masking discoloration. In general, chelated Fe + N tank-mixed with quinclorac masked discoloration and turf had quality equivalent to untreated bentgrass on most, but not all rating dates..

Derr, J. F.. 2002. Detection of fenoxaprop-resistant smooth crabgrass (Digitaria ischaemum) in turf. Weed Technology 16 : 396 - 400.

Greenhouse studies verified that smooth crabgrass (D. ischaemum) from a golf course tee in southern New Jersey, USA was resistant to fenoxaprop-P, although smooth crabgrass from a nearby untreated rough was susceptible to this herbicide. Fenoxaprop-P-resistant plants were injured, however, when fenoxaprop-P was applied at levels above the maximum use rate for turf. Fenoxaprop-P applied postemergence at 0.76 kg a.i./ha, four times the maximum rate, reduced shoot weight of the resistant biotype by 35%, whereas application of 1.52 kg/ha, eight times the maximum rate, reduced shoot weight by 64%. Large crabgrass (D. sanguinalis) and the susceptible biotype of smooth crabgrass were controlled by fenoxaprop-P applied at 0.1 kg/ha. Fenoxaprop-susceptible and fenoxaprop-resistant biotypes of smooth crabgrass had a similar response to MSMA, dithiopyr, and quinclorac applied postemergence. The fenoxaprop-P-resistant smooth crabgrass biotype was controlled by the cyclohexanedione herbicides sethoxydim and clethodim, but the aryloxyphenoxypropionate herbicides fluazifop and quizalofop reduced shoot weight by only 15-66% depending on herbicide and rate..

Kuk YongIn ; Wu JingRui ; Derr, J. F. ; Hatzios, K. K.. 1999. Mechanism of fenoxaprop resistance in an accession of smooth crabgrass (Digitaria ischaemum). Pesticide Biochemistry and Physiology 64 : 112 - 123.

The potential mechanism of fenoxaprop resistance was investigated in a D. ischaemum accession from New Jersey, USA, exhibiting a R/S GR₅₀ ratio of 102. The patterns of absorption, translocation and metabolism of radiolabelled fenoxaprop were similar in resistant and susceptible plants. Acetyl-CoA carboxylase activity from susceptible plants was highly sensitive to fenoxaprop acid and fenoxaprop-ethyl, while the enzyme from the resistant accession was very resistant to fenoxaprop-ethyl and somewhat less resistant to fenoxaprop acid. It is concluded that a less sensitive form of acetyl-CoA carboxylase confers fenoxaprop resistance to the D. ischaemum accession..

Hall, J. C. ; Stephenson, G. R.. 1995. The basis for the synergizing and safening action of fenchlorazole-ethyl on the herbicidal activity of fenoxaprop-ethyl: a review. : 261 - 268.

Laboratory studies over the previous 7 years (including published work) showed that the amount of glutathione (GSH) is higher in grass species that are moderately tolerant (wheat) and moderately susceptible (barley) to fenoxaprop-ethyl (FE) than in species that are very susceptible to the herbicide such as Avena fatua, Echinochloa crus-galli, Digitaria ischaemum and Setaria glauca [S. pumila]. Studies revealed that FE was rapidly hydrolysed to fenoxaprop (F) in wheat, barley and all weed species. In wheat and barley, F underwent some metabolism to 6-chloro-2,3-dihydrobenzoxazol-2-one (Hoe 054014) and rapid displacement of the phenyl group of F by GSH and/or cysteine, resulting in the production of a GSH conjugate, a cysteine conjugate, and 4-hydroxyphenoxypropanoic acid. There was considerably less metabolism of F in A. fatua, E. crus-galli, D. ischaemum and S. glauca. The triazole, fenchlorazol-ethyl (FCE), acts as a safener against the phytotoxic action of FE in wheat and barley, and as a synergist for the herbicide in E. crus-galli, D. ischaemum and S. glauca. However, FCE has no synergistic or safening effect on the toxicity of FE when applied to A. fatua. In addition, FCE increased the quantity of GSH in barley and wheat but had no effect on GSH levels in A. fatua, E. crus-galli, D. ischaemum and S. glauca. Consequently, in the presence of FCE, more F was non-enzymatically detoxified by conjugation with GSH and cysteine in wheat and barley than in the absence of FCE thereby safening both species against damage by the herbicide. In the presence of FCE, FE was rapidly converted to the more phytotoxic F in the susceptible species with little subsequent metabolism. This resulted in synergism in E. crus-galli, D. ischaemum and S. glauca. This did not happen in A. fatua since FCE was rapidly metabolized to water-soluble metabolites before it could mediate enhanced de-esterification of FE..

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