We live in Alexandria VA and we get that, too, with our oaks-willow, pin, red, etc. I am hoping it is squirrels, those nasty little rodents who eat all my bird seed-lol. I always figured they either like to watch me work picking up their discards or it is a diversion so they can raid the feeder while I am otherwise occupied. Anyway, we seem to have this every year and in the spring we get clumps of green leaves as well. So far, no permanent damage from the lost branchlets (is that a word???), although we did lose one oak to borers over a year ago and another this spring for unknown reason. So sad. I haven't noticed spots on ours, though. Sorry I can't be more help. Cynthia