Question
I have three holly trees which are robust and normally healthy; the trees are all in full bloom.  Now the leaves are covered in a soot-like black substance (which does not blow off) while new leaves are pushing up from the branch terminals.  Is this a fungus or a mite infestation - or something else?  Any suggestions would be much appreciated.

Answer
Check a couple of things--if the leaves are sticky this is an insect either an aphid scale. These insects suck the plant juices from the plant and secrete a substance called honeydew which is high in sugar content and sticky. A sooty mold will grow on this honeydew. Spray the holly with an insecticide called Orthene. Make sure you spray down into the foliage and try to wet good. This will control the sucking insects and the sooty mold will stop growing. The black sooty mold will then have nothing to feed on and will be washed off with rains. The sooty mold is not a problem and will go away after the aphids are controlled.  IF the tree is too large to reach all the foliage then treat the soil around the tree with an insecticide called Bayer Advanced Tree and Shrub Insect control. The roots will carry the insecticide to the foliage and twigs and when the insets feed they are killed. Here is a web link to this product.

http://www.bayeradvanced.com/tree-shrub-care/products/12-month-tree-shrub-insect...

IF the leaves are not sticky then this is a fungi growing on the leaves. Treat with a copper based fungicide. Spray the foliage and repeat in about three weeks and this should control the fungi. Check with your local garden  type store for these products.