title: Efficacy and environmental fate of imazapyr from directed helicopter applications targeting Tamarix species infestations in Colorado.
abstract: BACKGROUND
  Aerial imazapyr applications are the most common and cost-effective method for controlling invasive tamarisk, but few studies have investigated whether or how infestation and site characteristics influence control and non-target impacts. This study used vertical stands with filter papers, plus soil and tree canopy sampling, to investigate how tamarisk canopies affected retention of applied imazapyr, soil herbicide residues and tree mortality.
  
  
  RESULTS
  Tamarisk canopies captured 71% of aerially applied imazapyr, resulting in significantly lower soil residues beneath the tree canopy. Although initial imazapyr soil residue levels outside the tree canopy were 4 times greater than those inside, soil degradation occurred 2.4 times faster outside the tamarisk canopy and resulted in lower herbicide residues. Tamarisk mortality within 3 years was 70%, but variability in control appeared to be affected by non-linear stand boundaries and tall site obstructions. These same factors also increased variability in the actual quantity of herbicide applied, exacerbating collateral impacts on desirable understory species.
  
  
  CONCLUSIONS
  While aerial imazapyr applications are highly effective in controlling tamarisk, our study provides evidence for the importance of evaluating overall site suitability for this management strategy so the probability of unintended ecological effects can be minimized.
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, USA.|Environmental Science Program, Trinity College, Hartford, CT, USA.
authors.forename: Cameron H
authors.identifier: http://orcid.org/0000-0002-8738-6887
authors.initials: CH
authors.lastname: Douglass
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, USA.
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Nissen
authors.affiliation: Department of Plant Sciences, University of Wyoming, Laramie, WY, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Kniss
mesh_terms: D000336:Aerosols; D000401:Aircraft; D003120:Colorado; D004777:Environment; D006540:Herbicides / Q000737:chemistry / Q000494:pharmacology*; D007093:Imidazoles / Q000737:chemistry / Q000494:pharmacology*; D009525:Niacin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry / Q000494:pharmacology*; D032363:Tamaricaceae / Q000187:drug effects*
chemical_list: D000336:Aerosols; D006540:Herbicides; D007093:Imidazoles; D012987:Soil; D012989:Soil Pollutants; D009525:Niacin; C076656:imazapyr
keywords: helicopter herbicide applications; herbicide soil degradation; saltcedar; tamarisk