Effects of Herbicide on the Invasive Biennial Alliaria petiolata (Garlic Mustard) and Initial Responses of Native Plants in a Southwestern Ohio Forest

Abstract

Restoration often includes control of invasive plants, but little is known about how native plant communities respond to this control. The biennial Alliaria petiolata (M. Bieb.) Cavara and Grande (garlic mustard) is one of the most prevalent invasive plants in forests of eastern North America. We investigated the effects of the herbicide Round-up (glyphosate) on Alliaria and the response of the forest floor plant community to the herbicide and the subsequent decline of Alliaria. In an old-growth Acer-Fagus stand and a second-growth Liriodendron-dominated stand in Hueston Woods State Nature Preserve, Ohio, United States, we spot applied Round-up in November 2000 and 2001 in 25 1 · 1-m plots and maintained 25 control plots. Herbicide decreased Alliaria density in both stands and reduced the density of other species in leaf during treatment (mostly exotic winter annuals) in the old-growth stand. Treatment did not affect the initial density of the Alliaria cohort that germinated in the spring of 2001, but decreased the 2002 cohort. Community differences were found in the old-growth stand after Alliaria reduction, specifically greater cover of spring ephemerals in the herbicide treatment. In the second-growth stand, herbicide treatment increased reproduction of the late-summer perennial, Phryma leptostachya. These results indicate that glyphosate reduces Alliaria without negatively impacting native species and that some native species respond positively to a single-year reduction in this invasive biennial.

Relative allelopathic potential of invasive plant species in a young disturbed woodland1

“…For this reason, allelopathy may be more important in certain species rather than vary consistently across life forms. The invasive herbs Alliaria petiolata and Microstegium vimineum spread rapidly in forest understories in a variety of light conditions (Morrison et al 2007) and appear to be strong competitors relative to many native understory herbs (Carlson and Gorchov 2004, Stinson et al 2006, Morrison et al 2007, Oswalt et al 2007, but see Meekins and McCarthy 1999). Likewise, allelopathy may enhance the competitive success of the weedy and shade intolerant tree, Ailanthus altissima, which often regenerates in large canopy openings where competition may be intense.…”

Efficacy of Treatments against Garlic Mustard (Alliaria petiolata) and Effects on Forest Understory Plant Diversity

“…This corresponded with the growing season for spring ephemerals at the site, which increased non-target impacts of treatment. While early spring application of herbicide has been recommended to minimize impacts to native plants [17], fall herbicide application may be more advantageous [18,19], and would be expected to have limited the impact to understory diversity that was found in our study.…”

“…Repeated treatments of garlic mustard in heavily invaded sites using herbicide over multiple years have shown effectiveness in reducing adult plants [18,20]. Where forest understory has also been assessed, multiple year treatment with herbicide and fall application has shown minimal effects on species diversity, with some changes in community composition [18,19].…”

The Global Garlic Mustard Field Survey (GGMFS): challenges and opportunities of a unique, large-scale collaboration for invasion biology

“…Alliaria petiolata invades nutrient-rich, semi-shaded habitats such as forest edges and moist woodlands. Dense invasive populations can reduce native plant diversity and limit recruitment of native trees (Carlson and Gorchov 2004;Stinson et al 2007) by disrupting mycorrhizal communities that are important for economically valuable trees and native understory plants (Stinson et al 2006;Burke 2008;Wolfe et al 2008;Barto et al 2011;Lankau 2011), and by altering litter decomposition as well as soil nitrogen and phosphorus cycles .…”