title: Estimating economic thresholds for site-specific weed control using manual weed counts and sensor technology: an example based on three winter wheat trials.
abstract: BACKGROUND
  Precision experimental design uses the natural heterogeneity of agricultural fields and combines sensor technology with linear mixed models to estimate the effect of weeds, soil properties and herbicide on yield. These estimates can be used to derive economic thresholds. Three field trials are presented using the precision experimental design in winter wheat. Weed densities were determined by manual sampling and bi-spectral cameras, yield and soil properties were mapped.
  
  
  RESULTS
  Galium aparine, other broad-leaved weeds and Alopecurus myosuroides reduced yield by 17.5, 1.2 and 12.4 kg ha(-1) plant(-1)  m(2) in one trial. The determined thresholds for site-specific weed control with independently applied herbicides were 4, 48 and 12 plants m(-2), respectively. Spring drought reduced yield effects of weeds considerably in one trial, since water became yield limiting. A negative herbicide effect on the crop was negligible, except in one trial, in which the herbicide mixture tended to reduce yield by 0.6 t ha(-1). Bi-spectral cameras for weed counting were of limited use and still need improvement. Nevertheless, large weed patches were correctly identified.
  
  
  CONCLUSIONS
  The current paper presents a new approach to conducting field trials and deriving decision rules for weed control in farmers' fields.
authors.affiliation: Department of Weed Science, University of Hohenheim, Institute for Phytomedicine, Germany.
authors.forename: Martina
authors.initials: M
authors.lastname: Keller
authors.forename: Christoph
authors.initials: C
authors.lastname: Gutjahr
authors.forename: Jens
authors.initials: J
authors.lastname: Möhring
authors.forename: Martin
authors.initials: M
authors.lastname: Weis
authors.forename: Markus
authors.initials: M
authors.lastname: Sökefeld
authors.forename: Roland
authors.initials: R
authors.lastname: Gerhards
mesh_terms: D032061:Galium / Q000187:drug effects / Q000254:growth & development; D006540:Herbicides / Q000633:toxicity; D031168:Matricaria / Q000187:drug effects / Q000235:genetics; D012621:Seasons; D014908:Triticum; D058728:Weed Control / Q000191:economics* / Q000295:instrumentation*
chemical_list: D006540:Herbicides
keywords: bi-spectral camera; linear mixed models; site-specific herbicide application; weed distribution