title: Phorate can reverse P450 metabolism-based herbicide resistance in Lolium rigidum.
abstract: BACKGROUND
  Organophosphate insecticides can inhibit specific cytochrome P450 enzymes involved in metabolic herbicide resistance mechanisms, leading to synergistic interactions between the insecticide and the herbicide. In this study we report synergistic versus antagonistic interactions between the organophosphate insecticide phorate and five different herbicides observed in a population of multiple herbicide-resistant Lolium rigidum.
  
  
  RESULTS
  Phorate synergised with three different herbicide modes of action, enhancing the activity of the ALS inhibitor chlorsulfuron (60% LD50reduction), the VLCFAE inhibitor pyroxasulfone (45% LD50reduction) and the mitosis inhibitor trifluralin (70% LD50reduction). Conversely, phorate antagonised the two thiocarbamate herbicides prosulfocarb and triallate with a 12-fold LD50increase.
  
  
  CONCLUSIONS
  We report the selective reversal of P450-mediated metabolic multiple resistance to chlorsulfuron and trifluralin in the grass weed L. rigidum by synergistic interaction with the insecticide phorate, and discuss the putative mechanistic basis. This research should encourage diversity in herbicide use patterns for weed control as part of a long-term integrated management effort to reduce the risk of selection of metabolism-based multiple herbicide resistance in L. rigidum. © 2016 Society of Chemical Industry.
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology, University of Western Australia, Perth, WA, Australia.
authors.forename: Roberto
authors.initials: R
authors.lastname: Busi
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, USA.
authors.forename: Todd Adam
authors.identifier: http://orcid.org/0000-0003-1485-7665
authors.initials: TA
authors.lastname: Gaines
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology, University of Western Australia, Perth, WA, Australia.
authors.forename: Stephen
authors.initials: S
authors.lastname: Powles
mesh_terms: D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology*; D007306:Insecticides / Q000494:pharmacology; D008129:Lolium / Q000187:drug effects* / Q000378:metabolism; D010574:Pesticide Synergists; D010702:Phorate / Q000494:pharmacology*
chemical_list: D002800:Cholinesterase Inhibitors; D006540:Herbicides; D007306:Insecticides; D010574:Pesticide Synergists; D010702:Phorate; D003577:Cytochrome P-450 Enzyme System
keywords: agriculture; herbicide resistance; herbicide solutions; metabolism; ryegrass; weed control