I live in Redmond, WA (Western WA.) One of my dahlia beds doesn't get as much sun, it's more a partial sun bed. It's not one of my best beds, but the dahlia's do okay. I have this plant pest that may be some kind of bryophyte that has always been a pest, but this year is way out of hand and has almost taken over the bed. I'm looking for answers. Anyone know what it is and/or how to get rid of it? Just peeling it off and getting rid of what can be seen doesn't do it. Help would be appreciated! Here's the picture

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