Lesser Celandine (Ficaria verna), also called Fig Buttercup and Pilewort, is a highly invasive, nonnative plant in the eastern half of the United States. It is a perennial that is very difficult to control once it gets established. If you do a search online for ways to control it, you find a wide variety of suggestions, but not a lot of evidence on how successful each method is. We established over fourteen test plots in early 2021 to test some of the methods to see what works. We tracked each method for a year to see which methods are truly useful, and which methods just look good for the short haul, but don't do anything to reduce the number of Lesser Celandine plants.

We looked at mechanical means such as mowing, burning, and mulching with both clear and black plastic. We also tried some “environmentally friendly” chemical methods such as treating with 5%, 15%, and 30% vinegar (acetic acid), and 1.5% chelated iron. Our tests showed that all of these methods just impacted the aboveground portion of the plants and did nothing to kill the extensive roots and tubers underground. We also tested 4%, 3% and 1.5% of the nonselective herbicide glyphosate (ShoreKlear Plus), and 12%, 6%, and 3% of the broadleaf herbicide triclopyr ester (Alligare Triclopyr 4). All concentrations of glyphosate were successful at killing off all of the Lesser Celandine after one treatment. The test plots treated with glyphosate had full coverage of nontarget vegetation two months after treatment, showing that the glyphosate only killed off the vegetation that was leafed out at the time of treatment. The three dilutions of the triclopyr were successful at killing off the Lesser Celandine after one treatment, but the concentrations were high enough to also kill off all the other vegetation in the test plots throughout the first growing season. (We are running new tests on different concentrations of the triclopyr ester, along with trials with the triclopyr salt and other broadleaf lawn formulations. Watch for videos with those results in the summer of 2022 and the spring of 2023.)

Our conclusion is that successfully controlling Lesser Celandine involves: 1) keeping it out of a site by not intentionally planting it or unintentionally introducing it through mud or dirt on shoes or equipment from infested sites, and 2) treating it as soon as possible with an appropriate herbicide. While many people are reluctant to use herbicides, the environmental consequence of allowing Lesser Celandine to continue to spread and choke out native vegetation makes the careful use of herbicides the most environmentally friendly choice. Glyphosate has a relatively short halflife in the soil, does not migrate easily through clay soils, and does not kill any plants that it does not come in direct contact with the leaves. It does not kill through root uptake. While there is still more to learn, it is nice to know what methods are not worth our time and effort.

Oak Haven is a 60acre private woodland in Southwestern Ohio near Cincinnati. Jim and Julie Varick both have degrees in Botany and over thirty years of experience in managing natural areas. They enjoy sharing their enthusiasm for the natural world and would like to build relationships with likeminded people to share knowledge and resources.