Does anyone know a good site that will help to ID a lawn disease? I was looking for a place that starts out with (close up) pictures of different diseases and then you can drill in from there. The sites I've been on start with the name and an ambigous description. This makes it harder to pinpoint the problem.

From what I can tell so far, my problem seems to match powdery mildew in description, but not by photo. So I am stuck.

What I have is something that looks like dark/purplish little mold spore looking things (definetly a spore, not just a powder) growing on the tips of the blades in small areas throughout the yard. The grass blades dont seem dead, but are a deep green, almost black, color when compared to the surrounding turf. When brushing your hand throug it, a fine dust cloud rises. The area is not excessivley shaded.