title: Analysis of oilseed rape stem weevil chemical control using a damage rating scale.
abstract: BACKGROUND
  Rape stem weevil (Ceutorhynchus napi Gyll.) and cabbage stem weevil (C. pallidactylus Marsh.) can cause significant yield losses to oilseed rape (Brassica napus L.), and chemical control is often needed to protect crops from these pests. The efficacy of six insecticides, chlorpyriphos + cypermethrin, bifenthrin, alpha-cypermethrin, pirimiphos-methyl, thiacloprid and tau-fluvalinate, was tested in a 4 year field trial. Besides the standard efficacy analysis expressed through the number of larvae per stem, a damage rating scale was introduced and modelled using a regression model for ordinal categorical data.
  
  
  RESULTS
  Compared with the control, expressed through damage rating and larval number, treatments with chlorpyriphos + cypermethrin and bifenthrin, showed higher efficacy in the control of stem weevils compared with alpha-cypermethrin and pirimiphos-methyl. The lowest efficacy was observed in treatments with tau-fluvalinate and thiacloprid.
  
  
  CONCLUSIONS
  This study showed that a combined efficacy evaluation expressed through both damage rating scale and the count of larvae, supported by an ordinal regression model for data analysis, is indispensable for obtaining accurate results. © 2017 Society of Chemical Industry.
authors.affiliation: Institute of Field and Vegetable Crops, Novi Sad, Serbia.
authors.forename: Željko
authors.initials: Ž
authors.lastname: Milovac
authors.affiliation: Institute of Field and Vegetable Crops, Novi Sad, Serbia.
authors.forename: Miroslav
authors.initials: M
authors.lastname: Zorić
authors.affiliation: Institute of Field and Vegetable Crops, Novi Sad, Serbia.
authors.forename: Filip
authors.initials: F
authors.lastname: Franeta
authors.affiliation: Institute of Field and Vegetable Crops, Novi Sad, Serbia.
authors.forename: Sreten
authors.initials: S
authors.lastname: Terzić
authors.affiliation: Faculty of Agriculture, University of Belgrade, Belgrade, Serbia.
authors.forename: Olivera
authors.initials: O
authors.lastname: Petrović Obradović
authors.affiliation: Institute of Field and Vegetable Crops, Novi Sad, Serbia.
authors.forename: Ana
authors.initials: A
authors.lastname: Marjanović Jeromela
mesh_terms: D000818:Animals; D007306:Insecticides; D007814:Larva; D010571:Pest Control / Q000706:statistics & numerical data*; D048889:Weevils
chemical_list: D007306:Insecticides
keywords: Ceutorhynchus napi; Ceutorhynchus pallidactylus; chemical control; insecticide efficacy; proportional odds model