I would treat the shakes with a 3% solution very theroughly. All of the moss and such will die. Give it a couple weeks for the moss to dry and become brittle. Then using a wide sweep broom, broom off the dried and brittle moss and leaves. Apply more chemical to get the areas you missed the first time that are now exposed by the brooming. Do not exceede a 3% solution.
I don't see the big deal. It is just moss. It is a plant. We all know how to kill plants on purpose or by accident...lol. You aren't that far. I'll come down and knock it out for you.
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