title: Benchmark study on glyphosate-resistant cropping systems in the United States. Part 4: Weed management practices and effects on weed populations and soil seedbanks.
abstract: BACKGROUND
  Weed management in glyphosate-resistant (GR) maize, cotton and soybean in the United States relies almost exclusively on glyphosate, which raises criticism for facilitating shifts in weed populations. In 2006, the benchmark study, a field-scale investigation, was initiated in three different GR cropping systems to characterize academic recommendations for weed management and to determine the level to which these recommendations would reduce weed population shifts.
  
  
  RESULTS
  A majority of growers used glyphosate as the only herbicide for weed management, as opposed to 98% of the academic recommendations implementing at least two herbicide active ingredients and modes of action. The additional herbicides were applied with glyphosate and as soil residual treatments. The greater herbicide diversity with academic recommendations reduced weed population densities before and after post-emergence herbicide applications in 2006 and 2007, particularly in continuous GR crops.
  
  
  CONCLUSIONS
  Diversifying herbicides reduces weed population densities and lowers the risk of weed population shifts and the associated potential for the evolution of glyphosate-resistant weeds in continuous GR crops. Altered weed management practices (e.g. herbicides or tillage) enabled by rotating crops, whether GR or non-GR, improves weed management and thus minimizes the effectiveness of only using chemical tactics to mitigate weed population shifts.
authors.affiliation: University of Nebraska-Lincoln, Panhandle Research and Extension Center, Scotts Bluff, NE 69361-4939, USA. rwilson1@unl.edu
authors.forename: Robert G
authors.initials: RG
authors.lastname: Wilson
authors.forename: Bryan G
authors.initials: BG
authors.lastname: Young
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Matthews
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Weller
authors.forename: William G
authors.initials: WG
authors.lastname: Johnson
authors.forename: David L
authors.initials: DL
authors.lastname: Jordan
authors.forename: Micheal D K
authors.initials: MD
authors.lastname: Owen
authors.forename: Philip M
authors.initials: PM
authors.lastname: Dixon
authors.forename: David R
authors.initials: DR
authors.lastname: Shaw
mesh_terms: D000383:Agriculture; D019985:Benchmarking; D018556:Crops, Agricultural / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D005998:Glycine / Q000031:analogs & derivatives* / Q000032:analysis / Q000494:pharmacology; D053209:Herbicide Resistance; D006540:Herbicides / Q000032:analysis / Q000494:pharmacology*; D057685:Plant Weeds / Q000187:drug effects* / Q000254:growth & development; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D012987:Soil / Q000032:analysis; D014481:United States; D058728:Weed Control / Q000379:methods*; D000097797:Glyphosate
chemical_list: D005998:Glycine; D006540:Herbicides; D012987:Soil; D000097797:Glyphosate