Herbicides: an unexpected ally for native plants in the war against invasive species

Herbicides are primarily used for protecting agricultural crops from weeds and controlling vegetation competition in newly planted forest stands. Yet for over 40 years, they have also proven useful in controlling invasive plant species in natural areas. Nonnative invasive plant species, if not controlled, can displace native species and disrupt an ecosystem by changing soil chemical and biological properties. However, before an herbicide may be applied in a U.S. national forest, toxicological and ecological assessments and field testing are required to ensure it won’t negatively affect the landscape or people.

In the Gifford Pinchot National Forest, scientists with the U.S. Forest Service Pacific Northwest Research Station established experimental plots to test effects of aminopyralid (a plant growth-regulating herbicide) on both the nonnative and native meadow plant species. When applying less than the manufacturer’s maximum labeled rate, researchers found the herbicide reduced the cover of Canada thistle and other nonnatives without strongly affecting native species.

Aminopyralid, along with aminocyclopyrachlor and clopyralid (also plant growth-regulating herbicides), were also tested in a growth chamber trial for their effectiveness in controlling the germination of Scotch broom, a large invasive shrub that often reduces survival of young Douglas-fir. Spraying the soil with each type of herbicide controlled up to 90 percent of the germinating Scotch broom seedlings.

Citation

Watts, Andrea; Harrington, Tim; Peter, Dave. 2015. Herbicides: an unexpected ally for native plants in the war against invasive species. Science Findings 176. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 6 p.

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