Invasive Alert: Dealing with Lesser Celandine

Guest Blog by Meghan Fellow

Many of our Weed Warrior volunteers have sent in questions and concerns about Lesser Celandine (Ranunculus ficaria or Ficaria verna Huds.). Yes, it is getting worse. Floods and dispersal events spread this plant throughout our area. They are also extremely good and taking over new ground. Those pesky yellow carpets of weeds have replaced what should be a bounty of spring ephemerals (and their pollinators) are painful to watch -- we want to DO something.

Unfortunately, science has not kept up with our need. There is NO good, reliable way to kill celandine. Here are some popular suggestions: 

Dig it out.

Most people know not to pull it out -- those pesky underground bulbils stick around and thrive in the disturbed soil. So people have resorted to digging out the clumps whole. This can work in areas where the soil, moisture and all other factors are inline. It generates a ton of waste (soil and plant matter) and does a number on the health of the soil you're leaving behind. This waste cannot be home composted, so the only option is to send it to the county yard waste compost. This works best in garden beds or in very small infestations (1-10 plants). 

Dowse in 20% Acetic acid.

20% Acetic acid has been heralded as the organic alternate to glyphosate. Many people forget that when you're using it to kill plants it is a pesticide (not allowed for volunteers to use on parkland). However, let's explore this tool as to whether it is useful in a private situation. The mechanism of how it kills is important to consider when trying it out on a new species/situation. It is a top "burn" killer. Meaning above ground plant parts will die, but the roots do not die. Therefore this would best used on an annual plant, or in a situation where you could apply it repeatedly (not more often than every 2 weeks). 20% Acetic acid is actually recommended for sidewalk/driveway cracks and in gravel. But do be careful and wear protective gear, this is a strong acid and can burn. Household vinegar is 5% acetic acid and appears to have no consistent effect.

   Lesser celandine is a perennial -- 20% acetic acid is unlikely to have any long term effect. I know of no direct, replicated experimental studies on the species/treatment, only anecdotes.

Here is a paper from University of Maryland on the topic: http://extension.umd.edu/sites/default/files/_docs/programs/ipmnet/Vinegar-AnAlternativeToGlyphosate-UMD-Smith-Fiola-and-Gill.pdf
  

Burn it with flame weeding.

Flame weeding using a propane based torch is another method that achieves the top "burn." It leaves no residues at all in the soil. The roots/bulbils may or may not be affected. It has been used extensively for stiltgrass -- key thing to note, stiltgrass is an annual. Theory says flame weeding should not work on lesser celandine, but a few Weed Warriors and I have an extensive trial set up in Sligo, Little Falls and Capitol View Homewood Parks. We have been working on this since February. I hope to finish collecting data by late May, analyze it this summer and maybe have a new method for next year. Or at least an answer as to whether it might work.

Apply Glyphosate.

The only current reliable method of killing lesser celanine is to use glyphosate. As you all know we only use herbicides when it is absolutely necessary, and then in the minimum amount required. The protocol for lesser celandine control is to foliar spray celandine in the time in the spring after it has leaves but before it goes to flower (typically less than 50% of the plants have buds). This is an incredibly narrow window that we are now out of. This year it was about March 27-April 6. You must repeat this cycle for 3 years in a row.

    I read this summary as there is no good method for controlling celandine. Many people have told me what worked for them in their own garden, and we appreciate that -- we are looking at extensive infestations throughout parkland. All of the stream valleys and many of the parks in between do have celandine. This is a massive infestation. 

What can you do?

• Avoid areas with celandine. Avoid digging in them or even walking through them. In a few months (usually by mid-June) the celandine has senesced and you can go back to work.

• Garlic mustard on the other hand is out now, and there are key spots in the county that could use a lot of help (Sligo for one). Please pick garlic mustard! 

• Support efforts to research better ways to kill celandine.

•  Grow native ephemerals, if you can, in your own spaces. Studies have shown private yards can provide refugia for native pollinators and insects. 

• And please remind people not to plant lesser celandine! I've been told a number of stories of people removing it from parkland to put in their yards as it was "so pretty."

    I know this is a species that we have a great worry over. Thankfully there is a very small group of plants that are impossible to control with current methods. Unfortunately, this is one of them.

 

About the Author:

Meghan Fellows is the Weed Warrior Volunteer Coordinator with Montgomery County Parks. She can be reached at (301) 962-1343 or meghan.fellows@montgomeryparks.org. 

For more on invasive plants, see: www.WeedWarrior.org. Follow her on Twitter at https://twitter.com/parkweedwarrior.

Photo sources:
top -- Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

middle --  Meghan Fellows, Montgomery County Parks

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