Question
We have two trees that have the black leaf fungus all over them.  These trees are
very large and there is no way we could reach to spray them.  Is there a chemical
we could introduce systemically to control this?  The leaves that drop are very
sticky and a mess to clean up.

Answer
Hi there. What are describing is sooty mold. A by product of an aphid infestation. You can treat the trees for aphids with Bayer Advanced Garden?Tree and Shrub Insect Control.
For additional treatment options, contact a local professional arborist.
Caution: read all label instructions before using any pesticide, avoid skin
contact, and store pesticides  where children cannot reach them.
Hope this helps,Bill