Question

White spots  

White spots   Three or four years ago I planted a fruitless mulberry tree in my backyard I have since noticed the growth is very small in comparison to another Mulberry we planted 10 years ago the tree in question has white spots on the trunk. The leaves are green it seems healthy but the white spots seem to be stunting the growth rate. It has only grown about 2 to 3 feet in the last three years. Whereas my original mulberry tree was at 30 feet in width within three years. I'm wondering if it's worth saving or should I replant if new one.

Answer
The spots are lichens and will not harm the tree. 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.

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 abundance of lichens are a symptom that something else is causing the problem. The growth of the lichens means they are taking advantage of the sun light exposure caused by the thinning foliage.  

I would try fertilizing the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameyer. Scatter this around the tree and water it in. If you apply the fertilizer just before a rain event you will not have to water. This should increase the tree growth and shade out the lichens. Make sure you do not treat the lawn with a product called Weed and Feed this contains a herbicide that will damage the growth of the tree.