Lesser celandine, Ranunculus ficaria, is an invasive species on which little research has been performed to date. In a field experiment, we studied methods of R. ficaria control and the effects of different control methods on the response of the native understory. In a fully factorial study, we used two different types of herbicide (glyphosate or imazapyr), two different concentrations of herbicide (1.5% or 3% v/v) and two different times of herbicide application (pre-flowering in mid-March, flowering in early April, or post-flowering in early May). Treatments were applied in 2 x 2 m plots in heavily invested riparian areas (100% cover of R. ficaria in each plot) at three different sites in southwestern Ohio. Treatment combinations were replicated three times per site. One year later, plots were measured for percent cover of R. ficaria and percent cover of native species.
Results/Conclusions
We found that there were differences among sites in efficacy of control and in the effects on native species, which are likely related to differences in original conditions at each site. Imazapyr was most effective in reducing R. ficaria regardless of application time. In comparison, the effectiveness of application of glyphosate decreased over the season. Higher concentrations of herbicide led to slightly more control of R. ficaria, but also had much greater impacts on native species. Application in early May had the greatest negative impact on native species, followed by application in mid-March. Taking all factors into account, including differences between sites, we recommend using imazapyr during the flowering period (early April), followed by glyphosate or imazapyr during pre-flowering period (mid-March) using concentrations of 1.5%.