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The bane of weed management: Secondary invasions

Posted date: August 03, 2016

New research shows treatments for invasive plants yield unexpected consequences

Missoula, Mont., May 10, 2016 – Exotic plant invaders are global threats to ecosystems and millions of dollars are spent each year to fight invasions. A new study shows that current treatment methods could inadvertently promote a second invasion by exotic plants instead of desired native plants and negatively impact ecosystem restoration.

Secondary Invasions: The Bane of Weed Management, featured by the publisher Elsevier this month, reviews the effectiveness of invasive plant treatment methods and provides management suggestions for improved results.

The study considered 108 exotic plant species, including trees, shrubs, grasses, vines and forbs. Treatment methods investigated involved herbicides, mechanical means and biological controls. Treatments were commonly effective at removing the target invasive plant. However, secondary invaders (non-target exotic plants) increased after the treatment more than natives. Eighty-nine percent of these secondary invaders were classified as noxious weeds or invasive plants and can pose significant risk to native ecosystems. In general, the more successful the initial treatment, the greater the response of undesirable secondary invaders.

The researchers evaluated why the secondary invasions occur and suggested it is primarily the result of a ‘hole’ left after initial treatment, although some management approaches can exacerbate secondary invasions. Lead scientist, Dean Pearson of the U.S. Forest Service Rocky Mountain Research Station said “it was disconcerting to see that a common response to successful weed control was invasion by other noxious weeds.” He continued “the important message here is that we need to move beyond weed management to vegetation management to address secondary invasion.”

Strategies to refine weed control efforts to reduce unwanted secondary invasions are suggested in the paper. These strategies mainly focus on anticipating secondary invaders; building in management strategies to address them in conjunction with the target invader (e.g., using multiple techniques, like mixing mechanical and herbicide treatments); and/or filling the resulting 'hole' using native plant restoration efforts. Applying these strategies can facilitate more holistic invasive plant management and help reduce secondary invasions.



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Pearson, Dean E. ; Ortega, Yvette K. ; Runyon, Justin B. ; Butler, Jack L. , 2016

The Rocky Mountain Research Station (RMRS) is one of seven units within the U.S. Forest Service Research and Development. RMRS maintains 14 field laboratories throughout a 12-state territory encompassing parts of the Great Basin, Southwest, Rocky Mountains, and the Great Plains. RMRS also administers and conducts research on 14 experimental forests, ranges and watersheds and maintains long-term research databases for these areas. While anchored in the geography of the West our research is global in scale. To find out more about the RMRS go to You can also follow us on Twitter at




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National Strategic Program Areas: 
Invasive Species
National Priority Research Areas: 
Localized Needs
RMRS Science Program Areas: 
Wildlife and Terrestrial Ecosystems
RMRS Strategic Priorities: 
Disturbance Ecology
Jennifer Hayes
Public Affairs Specialist