Effects of herbicide type, herbicide concentration, and date of application on control of lesser celandine ( Ranunculus ficaria ) and on response of native species

Lesser celandine, Ranunculus ficaria L., is an ephemeral perennial invasive species on which limited research has been conducted. 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 full-factorial study, we used two different types of herbicides (glyphosate or imazapyr), two different concentrations of herbicide (low or high) and three different dates 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 infested 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. Imazapyr was most effective in reducing R. ficaria regardless of application date, while the effectiveness of application of glyphosate decreased over the season. The presence of native species one year later was affected by date of application. Application in mid-April led to greater native species cover than application in early May, with applications in mid-March intermediate between the two. We found that there were differences among sites in efficacy of control and in the cover of native species, which are likely related to differences in conditions at each site.