Assessment of treatment methods for the invasive exotic plant garlic mustard (Alliaria petiolata)

Background/Question/Methods

Garlic mustard (Alliaria petiolata) is an invasive exotic biennial herb native to Europe. When established in North America, it can out-compete native vegetation and impact ecosystem function. Garlic mustard has been identified in the Upper Peninsula of Michigan, but is not yet widely distributed. The objective of this research was to test the effectiveness of control methods for garlic mustard in Upper Peninsula hardwood forests. Six treatment types were selected: control, hand-pull, herbicide, hand-pull/herbicide, scorch, and hand-pull/scorch. The treatments were applied at three sites in a hardwood forest invaded by garlic mustard. Vegetation was sampled within the treatment plots to compare garlic mustard abundance, broken down by first and second year plants, and native plant diversity.
Results/Conclusions

Results immediately following treatment indicated that garlic mustard was significantly reduced by herbicide, hand-pull/herbicide, scorch, and hand-pull/scorch treatments. However, sampling of the treatment sites one year later showed an increase in first year garlic mustard plants to levels higher than those present before treatment application in the herbicide, hand-pull/herbicide, scorch, and hand-pull/scorch treatments. The hand-pull treatment resulted in an initial decrease in second year plants, but after one year did not differ significantly from the control. In this study, treatment of garlic mustard with hand-pulling, herbicide, and/or scorching was not effective. Furthermore, the results suggest that treatment of garlic mustard, and the surrounding vegetation, with herbicide or scorching may give garlic mustard an advantage over native vegetation when re-colonizing treated areas.