title: Why was resistance to shorter-acting pre-emergence herbicides slower to evolve?
abstract: BACKGROUND
  Across several agricultural systems the evolution of herbicide resistance has occurred more rapidly to post-emergence than pre-emergence herbicides; however, the reasons for this are not clear. We used a new simulation model to investigate whether interactions between differences in order of application and weed cohorts affected could explain this historically observed difference between the herbicide groups.
  
  
  RESULTS
  A 10 year delay in resistance evolution was predicted for a shorter-acting residual pre-emergence (cf. post-emergence), when all other parameters were identical. Differences in order of application between pre- and post-emergence herbicides had minimal effect on rates of resistance evolution when similar weed cohorts were affected.
  
  
  CONCLUSIONS
  This modelling suggested that the historically observed lower levels of resistance to pre-emergence herbicides are most likely to be due to the smaller number of weed cohorts affected by many pre-emergence herbicides. The lower number of weed cohorts affected by pre-emergence herbicides necessitated the use of additional, effective control measures, thereby reducing resistance evolution. This study highlights the advantages of applying multiple control measures to each weed cohort. © 2016 Society of Chemical Industry.
authors.affiliation: Australian Herbicide Resistance Initiative, School of Agriculture and Environment, University of Western Australia, Perth, WA, Australia.
authors.forename: Gayle J
authors.initials: GJ
authors.lastname: Somerville
authors.affiliation: Australian Herbicide Resistance Initiative, School of Agriculture and Environment, University of Western Australia, Perth, WA, Australia.
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Powles
authors.affiliation: Australian Herbicide Resistance Initiative, School of Agriculture and Environment, University of Western Australia, Perth, WA, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Walsh
authors.affiliation: Australian Herbicide Resistance Initiative, School of Agriculture and Environment, University of Western Australia, Perth, WA, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Renton
mesh_terms: D019143:Evolution, Molecular; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology*; D008954:Models, Biological; D010573:Pesticide Residues / Q000494:pharmacology; D057685:Plant Weeds / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
chemical_list: D006540:Herbicides; D010573:Pesticide Residues
keywords: Lolium rigidum; herbicide resistance; mode of action; population modelling; ryegrass