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Moss, Lichen, Extraterrestrial Invasion???? #749466

Asked May 12, 2021, 12:04 PM EDT

Would dearly love some help with this. Roundup products seem to have no effect. Products like Spray and Forget, and Spray and Walk Away may do something, but not much. Been around for 2 - 3 years now and just keeps spreading. So might you know what it is and is their a control product? I’ve resorted to scraping it off but am afraid I’m not getting all the roots.

Montgomery County Maryland

Expert Response

It's hard to concretely identify while dried and flaky, but this appears to be a type of Liverwort. They are cousins to moss and occur in similar environments - often shaded and damp. They don't have true roots, but can have tiny root-like structures that help them hold onto their substrate of choice. If plants are reappearing after removal, it's not because of left-behind roots in this case, but rather than the environment is well-suited to their growth and they are returning as a new generations from spores.

There are dozens of species found in MD; two commonly-encountered ones are shown in image galleries here, which you can compare to yours (when green); both are native:

https://www.marylandbiodiversity.com/view/8264

https://www.marylandbiodiversity.com/view/8262

They shouldn't harm anything if left alone, but if undesirable due to creating a trip or slip hazard, keep physically removing them and try to improve conditions so the area is less suitable for growth. Treatments with a registered herbicide product that is labeled for liverwort control (and likely also moss control) might clear-out existing populations but won't prevent new colonies from establishing later, unless it has a long residual. If the brick pavers are not near any highly-flammable material, you could try a flame weeder tool to see if it sterilizes the gaps between bricks. This will be a temporary measure, though, if the area stays moist enough that spores can re-colonize the area. (Is there a sprinkler system or leaking hose/downspout that frequently dampens the bricks?)

Aside from moss, which is treated like liverwort, the other possible identity of this residue is a cyanobacteria called Nostoc. They are fairly easy to differentiate from mosses and liverworts when living and green, as Nostoc has a jelly- or seaweed-like consistency, though they too darken and crisp when dry and re-animate or quickly re-colonize an area from spores after removal. Clemson has some more information on this organism: https://hgic.clemson.edu/factsheet/nostoc/

https://www.marylandbiodiversity.com/view/20912 


Miri

Thank you.  Huge help.  Definitely liverwort. It was a slip hazard.  I scraped up most of it.  Gonna’ have a go at the remainder with a 20% vinegar solution.  After that some sodium percarbonate.  At least now that it has a name I can develop a control plan.

On Wed, May 12, 2021 at 1:02 PM Ask Extension <<personal data hidden>> wrote:
The Question Asker Replied May 12, 2021, 2:17 PM EDT

You're welcome.

Horticultural-strength vinegar (acetic acid) may work, just use extreme caution in applying it as it is not only caustic to human tissues but will damage nearby plants as well. (Note: using household vinegar won't be effective, of which you may already be aware.)

Miri

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