A maple tree in my front yard gets blotchy gray and white spots on its leaves every summer. When the leaves fall in autumn they turn brown and have tiny gray spots all over. I thought this was mildew, but no one I know can tell. The problem is I'm afraid it transferred onto my garden plants. I had several healthy patches of catnip that began to show gray spots, and my basil and lemon balm both had brown edges on the leaves, which shriveled by summer's end.
Anyone know what it is and how to treat it (preferably organically)?