clodinafop and fenoxaprop-ethyl

Repeated use of acetyl-CoA carboxylase (ACCase) inhibitors, especially fenoxaprop and clodinafop, since the late 1980s has selected for resistance in Alopecurus myosuroides Huds. (black-grass) in France. We investigated whether resistance to pinoxaden, a phenylpyrazoline ACCase inhibitor to be marketed in France, was present in French black-grass populations. We investigated pinoxaden resistance conferred by five mutant ACCase isoforms. Using 84 French black-grass field samples, we also compared the frequencies of other mechanisms endowing resistance to fenoxaprop, clodinafop or pinoxaden.. ACCase mutant isoforms Leu-1781, Gly-2078 and, likely, Cys-2027 conferred cross-resistance to pinoxaden, while isoform Asn-2041 possibly conferred moderate resistance. Other mechanisms of resistance to fenoxaprop, clodinafop and pinoxaden were detected in 99, 68 and 64% of the samples investigated, respectively. Cross- or multiple resistance to fenoxaprop or clodinafop and pinoxaden was not systematically observed, suggesting a diversity of mechanisms exist.. Pinoxaden resistance was observed before pinoxaden release in France. Only a fraction of the mechanisms endowing fenoxaprop or clodinafop resistance also confer pinoxaden resistance. Pinoxaden resistance was likely mostly selected for by ACCase inhibitors, and, in some cases, possibly by herbicides with other modes of action. This illustrates the necessity to use metabolisable herbicides cautiously where black-grass has evolved non-target-site-based resistance.

Topics: Acetyl-CoA Carboxylase; Enzyme Inhibitors; France; Herbicide Resistance; Herbicides; Heterocyclic Compounds, 2-Ring; Mutation; Oxazoles; Plant Proteins; Poaceae; Propionates; Pyridines

Herbicide doses used by farmers are often lower than registration doses. One of the reasons put forward is that field assays for registration are performed at relatively high application volumes (typically 300 L ha(-1)), whereas farmers use lower volumes (down to 75 L ha(-1) or even lower). The resulting concentration of the active ingredient(s) and the formulants is supposed to enhance efficacy. To test this hypothesis in the case of specific graminicides, we compared the efficacy of clodinafop-propargyl and fenoxaprop-ethyl on Avena sativa at two application volumes. Fenoxaprop-ethyl was more efficacious when applied in 75 L ha(-1) as compared to 300 L ha(-1); ED95 were 20.0 and 26.0 g ha(-1), respectively. By contrast, clodinafop-propargyl exhibited the same efficacy under both conditions. Studies of dynamic surface tension showed differences in behaviour between spray dilutions of the two herbicides, especially at concentrations corresponding to ED95s. After 100 ms, surface tension decrease was lower than 2 mN m(-1) for clodinafop-propargyl at both application volumes. By contrast, surface tension decrease was 7 mN m(-1) for fenoxaprop-ethyl at 300 L ha(-1), and 18.5 mN m(-1) at 75 L ha(-1). In the case of fenoxaprop-ethyl sprayed at doses used in the practice, the retention of active ingredient by Avena sativa was lower at high application volume. This study shows that in some cases, concentration of the spray dilution may increase efficacy, formulation being probably involved.

Topics: Acetyl-CoA Carboxylase; Agriculture; Avena; Dose-Response Relationship, Drug; France; Herbicides; Oxazoles; Propanols; Propionates; Pyridines; Surface Tension

Black-grass (Alopecurus myosuroides Huds) is a major grass weed in winter cereals in Europe. It reduces yields and can act as a secondary host for a range of diseases. Herbicide resistance in this species was first detected in the UK in the early 1980s, and has now been reported in thirty counties. To successfully manage herbicide resistance it is vital that suspect populations are tested so that appropriate action can be taken. Ideally, a test will be quick, cheap and easy to use. Furthermore, it should provide an unequivocal result before post-emergence herbicides are to be applied, allowing alternative strategies to be adopted where necessary. This paper reports the development of new tests for herbicide resistance based on our observation that the resistant black-grass biotype Peldon contains approximately double the activity of the enzyme glutathione S-transferase (GST) compared with susceptible biotypes. Data are presented on the production of a monoclonal antiserum to a novel 30 kDa GST polypeptide purified from the biotype Peldon. An ELISA using this antiserum is described and the utility of this assay to detect resistant black-grass biotypes in plants grown under glass and in the field is presented. In addition, a microtitre assay for GST activity is described, which allows the rapid assessment of GST activities of plants. Both abundance and activity of GSTs are discussed as markers for herbicide resistance in black-grass.

Topics: Drug Resistance; Environment, Controlled; Enzyme-Linked Immunosorbent Assay; Glutathione Transferase; Herbicides; Methylurea Compounds; Oxazoles; Phenylurea Compounds; Poaceae; Propionates; Pyridines