Question
I have a bush in front of my house that was allowed to grow large like a tree.  In the Spring it gets puffy little buds that look like 'fuzzy' pussy willows. After they drop off, the bush gets leaves. Now, some green 'stuff' is growing on the bark and sap is coming out of the tree onto my driveway. What can I do to 'help' this tree/bush?  The green 'stuff' looks like mold and when I scrap my nail on it, it is like a powder---dry and loose.

Answer
The sap from the leaves is caused by an insect called an aphid or a scale insect. These suck the plant juices from the leaf and secrete a substance called Honeydew which is high in sugar content and sticky. Control the aphids and the sap will stop. Treat the aphids with an insecticide called Bayer Advanced Tree and Shrub Insect Control. This is applied to the soil around the tree and the roots transport the insecticide to the leaves and when the insect sucks the juices it is killed. Here is a web link to this product and you should be able to get it at your local nursery.

http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html

The green "stuff" is called lichens.

Lichens are an example of a symbiotic relationship between algae and certain fungi. They are capable of producing their own food. The algae associated with the fungus is a green or blue-green alga. There are three forms of lichens based on growth patterns. Crustose are species that are closely pressed against the surface of the limb or trunk of dead or live trees. Foliose forms are leaf like or prostrate but are also tightly attached to the tree. Fruticose forms are bush like, erect or hanging. Although lichens are found in most areas of Texas, they are most noticeable in areas that have extended periods of high humidity.

The effect of lichens on a tree are only slightly detrimental. The plants are epiphytes. That is they derive their nutrients from the air and not from the plant on which they are growing. Although they are not parasitized, literature reports suggest that lichens do have a slight negative effect. The main concern is that lichens give a tree an unkept appearance. Presence of lichens also is a good indicator of a thin tree canopy. This often leads homeowners to conclude that lichens are the cause and not the effect of thin foliage. The best control for lichens is maintain the tree in good condition. This will insure a dense canopy which will shade the limbs and reduce photosynthesis. Without photosynthesis, lichens are not able to manufacture food needed for growth and development.  

The baking soda recommendation I have heard of is 40 pounds of baking soda per 100 gallons which comes to 0.4 lb of baking soda to 1 gal of water. But I would not do anything about the lichens but I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. this will increase the overall health of the tree.