Alliaria petiolata, or garlic mustard, is an invasive plant species in forests of the Eastern and Midwestern USA. Native to Europe, this plant outcompetes native species for nutrients and space. Management of invasive plants like garlic mustard is costly and time consuming. Usually, such plants are managed using chemical herbicides. However, chemical herbicides can have adverse effects on the environment, such as polluting the groundwater and soil. It is therefore important to research alternative natural herbicides to find a more environmentally friendly but effective treatment. A review of the literature suggested that research is needed to answer the following questions: (1) Can vinegar and clove oil be used effectively against garlic mustard, as compared to Roundup®? and (2) What are the effects of these natural herbicides on the germination of high-quality native plant species? Garlic mustard and a native plant species, Ageratina altissima, were grown from seed on lit plant carts and sprayed with one of five treatments: water control, 15% acetic acid, 3.5% clove oil, 7% clove oil, or Roundup®. Green leaves were counted for one week after spraying. Native plant seeds were added to pots of the aforementioned treatments to assess impacts on germination and early growth.
Results/Conclusions
The alternative herbicides, vinegar and clove oil, had comparable effectiveness when compared to Roundup®. After one week, all treatments except the water control resulted in 90-100% leaf mortality. The native plant, Ageratina altissima, and garlic mustard were similarly negatively affected in all treatments. Of the four species of native plant seed added to the sprayed pots, only Blephilia hirsuta (hairy wood mint) had enough germination for analysis. A significantly smaller proportion of hairy wood mint seeds germinated in soils previously treated with Roundup® than the other four treatment groups. Biomass of hairy wood mint seedlings in soil previously treated with Roundup® did not significantly differ from the control and 3.5% clove oil treatments. Biomass was, however, greater in the 15% acetic acid and 7% clove oil treatment groups than the Roundup® group. These findings may have important implications for management of garlic mustard and reseeding of native species in plant community restoration projects. Future studies should investigate the efficacy of these alternative herbicides in the field and examine the success of reseeding native plant species after herbicide treatment.