Question
I have a row of older holly, that have been trimmed into a large hedge, 4 feet wide, 6 feet high that have black on the leaves that looks like it is soot.  It is on the lower leaves and seems to covering more leaves over time, moving upward.  Mainly on the north side of the plants.  We are in the mid-Atlantic area. I tried to wash the leaves with a heavy spray of water and some came off.  The leaves are not turning yellow and dropping, just more and more are getting this black, grit like covering.  I can't find anything written about this.  Thanks

Answer
What you are seeing is powdery mildew. This fungus grows on the sugar extract producd by aphids. Aphids are small soft bodied insects that suck the juices from plant leaves. They produce a sticky substance that the black mold grows on. The yellowing of the leaves is another sign of aphids. Control the aphids and the black will go away and wash off with the rains. Check with your local garden/ nursery type store and get a systemic insecticide for aphids. Spray this on both sides of the leaves and you will solve your problem.