Question
Hi Mr Hyland,  Our river birch is dripping sap or something AND dropping debris from small pine-cone shaped growths all over the tree. In addition, it seems to be afflicted (worse than usual) with some sort of infestation like powdery mildew or something that makes the leaves gnarled and sticky. The Bluegrass has had more rain than usual this spring, but this tree, which is about 20 years old, has never been so messy before. This stuff is all over our deck and the plants out back. Plus, I'm concerned about us breathing that powdery stuff.  Please advise.  Thank you and best,  Lorayne Burns

Answer
The dropping sounds like secretions from an insect called an aphid. These small bodied insects suck the plant juices from the leaf causing the leaf to curl. The substance is called honeydew--it is high in sugar content and feels sticky to the touch. Usually ants are present eating the honeydew. A black sooty mold will grow on the honeydew. The pine cone like growths are just that the  cones of the birch (fruit).  
Control the aphids and the sooty mold will go away. A tree this large (20 year old) will be hard to spray the foliage. I would recommend using a systemic insecticide applied to the soil. The trees roots will take the insecticide up to the leaves and when the insect sucks the juices it will die.

Certain insecticides that move systemically in the plant may provide control through the fall. Imidacloprid (Bayer Advanced Garden Tree and Shrub Insect Control) is a newly available systemic insecticide that can provide aphid control on trees for several months following application to the soil.