title: Challenges in devising economic spray thresholds for a major pest of Australian canola, the redlegged earth mite (Halotydeus destructor).
abstract: BACKGROUND
  A key component for spray decision-making in IPM programmes is the establishment of economic injury levels (EILs) and economic thresholds (ETs). We aimed to establish an EIL for the redlegged earth mite (Halotydeus destructor Tucker) on canola.
  
  
  RESULTS
  Complex interactions between mite numbers, feeding damage and plant recovery were found, highlighting the challenges in linking H. destructor numbers to yield. A guide of 10 mites plant(-1) was established at the first-true-leaf stage; however, simple relationships were not evident at other crop development stages, making it difficult to establish reliable EILs based on mite number. Yield was, however, strongly associated with plant damage and plant densities, reflecting the impact of mite feeding damage and indicating a plant-based alternative for establishing thresholds for H. destructor. Drawing on data from multiple field trials, we show that plant densities below 30-40 plants m(-2) could be used as a proxy for mite damage when reliable estimates of mite densities are not possible.
  
  
  CONCLUSIONS
  This plant-based threshold provides a practical tool that avoids the difficulties of accurately estimating mite densities. The approach may be applicable to other situations where production conditions are unpredictable and interactions between pests and plant hosts are complex.
authors.affiliation: Department of Zoology, Bio21 Institute, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Aston L
authors.initials: AL
authors.lastname: Arthur
authors.affiliation: Department of Zoology, Bio21 Institute, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Ary A
authors.initials: AA
authors.lastname: Hoffmann
authors.affiliation: Department of Zoology, Bio21 Institute, The University of Melbourne, Parkville, Victoria, Australia.|Cesar, Parkville, Victoria, Australia.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Umina
mesh_terms: D056810:Acaricides / Q000633:toxicity*; D000818:Animals; D001315:Australia; D029688:Brassica napus / Q000469:parasitology*; D008925:Mites / Q000187:drug effects* / Q000502:physiology; D010571:Pest Control / Q000191:economics / Q000379:methods*; D010935:Plant Diseases / Q000191:economics / Q000469:parasitology / Q000517:prevention & control*; D014675:Vegetables / Q000191:economics / Q000469:parasitology*
chemical_list: D056810:Acaricides
keywords: Halotydeus destructor; canola; economic injury levels; economic thresholds; pest; plant densities