Can you tell my why my arborvites have black on them?

  • Arborvitae
Hello, Bri.  Thank you for your question.
This is called “black flagging” but there isn’t much known about it.  No known cause or treatment is proven.  Some think it is due to animal urine since it is typically lower on the tree and in one area.  Trim out the black and put the clippings in the garbage.  The trees should be fine.  Here are a couple universities that are trying to learn more about the rare condition.

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