Question
We have lived in our home 20 years and the last two years have had a problem with a black residue covering our patio furniture, roof and plants in the backyard. We have a large oak tree, and many pines. We are familiar with pine pollen (yellow). We think it may be coming from the oak. Any clues?

Answer
Sounds like sooty mold. Sooty mold will grow on a substance called honeydew. Honeydew is a substance from scale or aphid insects. These insects suck the juices from plants and secrete this sap which is high in sugar content. The areas should fell sticky to the touch. To control the sooty mold you will need to control the aphids. More than likely the sap is coming from the oak. You can treat the scales and aphids with a product called Bayer Advanced Tree and shrub insect control. This systemic insecticide is applied to the soil under the tree and the roots will take it up to the foliage and when the sucking insects suck the juices they are killed.  The tree can be sprayed with Orthene but normally the tree is too large for most sprayer to reach all the foliage and a professional sprayer would be needed. The soil treatment can be done by the homeowner. Control the sucking insects and the sooty mold will go away since it has nothing to feed on.