Question
I planted several Rose of Sharon Trees a couple of years ago and they all seem to be growing fine. Near two of them I am noticing small dark reddish type marks all over the siding and windows of the house, as well as on the branches. The residue is very small but sticky and is difficult to get off the windows. I have had to take a scraper on several occasions to get it off. Is this some sort of disease on these trees, not all seem to have it?

Answer
Sounds like an insect either a scale or aphid. These insects suck the plant juice and secrete a substance called honeydew which is high in sugar content and sticky. It forms small droplets and can get on anything near the tree. I would control the sucking insects and this will stop the honeydew. Apply an insecticide called Bayer Advanced Tree and Shrub Insect control to the soil around the tree and the roots will pick it up and carry it to the plant leaves and twigs and when the insects feeds they will be killed. This treatment will last all season long. Check with your local garden type store for this product. Here is a web link to more information on this product.  http://www.bayeradvanced.com/tree-shrub-care/products/12-month-tree-shrub-insect