Question
I have a River Birch that was transplanted (south-central Ohio) 3 years ago and to date has thrived growing approximately 5 feet in that time. Just recently I have noticed an abundance of leaves turning yellow (~50%) and closer examination revealed the presence of a black coating on most of the tree limbs and part of the trunk. It looks similar to spray paint. Any treatment suggestions?

Answer
Hi Kelly

What you describe sounds like an aphid infestation.  These insects will leave a sugary substance on the leaf surfaces and will also drip onto the bark of branches.  On this sugary substance, called honeydew, a black sooty mold will gow.  The sooty mold is not parasitic to the tree and is of a secondary consequence.  The prime reason is the presence of the aphids.  Check the lower leaf surface for soft bodied, round, and most likely, green bugs.  If you see these then there is an aphid infestation.  They will not kill your tree, but can cause defoliation and bad appearance.  I would recommend treating the tree with Bayer Advanced Tree and Shrub Insecticide.  This product is mixed with water and poured on the soil surface around the base of the tree.  It is systemic and is taken up through the roots and will kill the bugs within a week or two.  This is good stuff.  I hope this helps fix the problem.  Good Luck.