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To spray or not to spray

Date: September 02, 2016

Assessing the impacts of biocontrol vs. herbicide application or no treatment on large scale, chronic Dalmatian toadflax infestations and non-target plant diversity in the Elkhorns Wildlife Management Area


Alex Gaffke (front) and Diane Johnson (back) measuring Dalmatian toadflax density and heights on a biocontrol site transect, July 2013.
Alex Gaffke (front) and Diane Johnson (back) measuring Dalmatian toadflax density and heights on a biocontrol site transect, July 2013.
The impacts of typical weed treatments on both the target weed(s) and non-target plant species that occur in large scale, chronic weed infestations are seldom quantitatively assessed or compared. Further, advantages or disadvantages of making high density ‘inundative’ biocontrol releases to counteract high levels of overwintering mortality affecting agent establishment and increase are seldom documented. Impacts of inundative biocontrol on Dalmatian toadflax abundance, non-target plant diversity, forage quality and quantity, and wildlife habitat quality will be assessed and compared to the impacts on the same resources either treated with aerial applied herbicides or left untreated.

The Elkhorns are a 300,000-acre island mountain range surrounded by small ranching communities. The Elkhorns’ diverse habitat features support abundant wildlife, while its natural resources have been the focus of human activities (mining, ranching, logging, livestock grazing, hunting and other recreational uses).

Alex Gaffke (left), Daniel Cook (center) and Chet Stefan (right) recording data on a helispray site transect, July 2016.
Alex Gaffke (left), Daniel Cook (center) and Chet Stefan (right) recording data on a helispray site transect, July 2016.
Natural and anthropogenic sources of disturbance have contributed to large scale, chronic and often inaccessible weed infestations. Implementing effective backcountry weed management is essential to minimizing treatment costs, avoiding deterioration of wildlife habitat, and maintaining or enhancing livestock forage production and native floral and faunal diversity. Although biological control is gaining favor as a long-term sustainable management strategy for weed infestations affecting cash-strapped public lands, its efficacy and safety remains largely unproven, especially at an operational scale.

This project compares the control efficacy and non-target impacts of biological control vs. the no treatment option or helicopter-applied herbicide treatments in Dalmatian toadflax infestations, under typical arid intermountain range conditions. Sequential plant inventories and assessment of plant cover by life form on fixed transects will provide a quantitative basis for these comparisons. This study will additionally supply important data that can be used to support NEPA analyses on future Forest Plans that include weed biocontrol as a proposed treatment.

Activities

  • Three treatment sites (helispray site, biocontrol site, no treatment or control site), each at least 300 acres in size, were selected in spring 2013. 

  • Ten permanently fixed transects were established on each of the three treatment sites. Measurements were taken to characterize the Dalmatian toadflax infestation and percent cover by vegetation life form within Daubenmire frames placed at fixed 2 m intervals along each of the 20 m transects (10 quadrats/20 m transect). Baseline measurements were taken on all three sites before any treatments began.

  • Presence/absence of 178 native and invasive plant species along each of the 30 transects in each site was also recorded. Plant identifications have been verified by USDA Forest Service and Montana State University botanists.

Additional Information 

Looking to the long-term: Forest Service combats weeds using insects to reduce herbicides 
Independent Record | July 24, 2016

Left: Dalmatian toadflax biocontrol site before treatment in 2013. Right: after treatment in 2016.
Left: Dalmatian toadflax biocontrol site before treatment in 2013. Right: after treatment in 2016.

 

Featured Publications

Sing, Sharlene E. ; De Clerck-Floate, Rosemarie ; Hansen, Richard W. ; Pearce, Hal ; Randall, Carol Bell ; Tosevski, Ivo ; Ward, Sarah M. , 2016
Wilson, Linda M. ; Sing, Sharlene E. ; Piper, Gary L. ; Hansen, Richard W. ; De Clerck-Floate, Rosemarie ; MacKinnon, Daniel K. ; Randall, Carol Bell , 2005


Principal Investigators: 
Principal Investigators - External: 
Diane L. Johnson - Helena National Forest
Forest Service Partners: 
Tracy Schilling, Helena National Forest
Anthony (Tony) Smith, Helena National Forest
Denise Pengeroth, Helena National Forest
Mandy Alvino, Helena National Forest
Andrew Hesse, Helena National Forest
External Partners: 
David K. Weaver, Montana State University
Tracy Sterling, Montana State University
Alexander Gaffke, Montana State University
Adam Cook, Montana State University
Daniel Cook, Montana State University
Chet Stefan, Montana State University
Tucker Colvin, Montana State University
Research Location: 
Montana