Trimmed shrubs at one of my commercial customers this week and noticed some black-looking stuff on the leaves.looks like diesel exhaust.Nearly all privits and foster hollys with plenty of air space around them.The plants all seem to be very healthy.It's not as bad on the sunny side of the building. We 've had a very wet sept. and oct. here. I have a pesticide training manual from U of Tn. and nothing really looks like this stuff .Powdery mildew is closest match but it's white or gray. Also these guys are not going to spend a whole lot on this right now. Thanks in advance for any ideas.