Question
i have a large double flower deep pink camealia, i have noticed on the leaves, a black tar like substance, which comes off when rubbed, it is also on the stems

any ideas julie

Answer
The problem sounds like an aphid infestation rather then disease. Aphids are small insects that suck the juices out of plant leaves and excrete a substance called honeydew--a sugar liquid that a fungus called black sooty mold grows on. The leaves should feel sticky.  Control the aphids and the black sooty mold will be washed off by the rains. Check with your local garden/nursery type store and ask for a systemic insecticide that will control aphids. Spray this on the under side as well as the upper side of all the foliage. Here is a web link to information on Black sooty mold:
http://ohioline.osu.edu/hyg-fact/3000/3046.html