Question
QUESTION: Again, we live in northeast Ohio. We so appreciated your answer to our last question that we have another problem for which we could use some help. This might be two different issues. We had a 40 foot oak tree which seemed completely healthy and yet died within a single year's time - actually by July it had suddenly died back (lower limbs 1st# and by August was completely dead. There was no sign of disease or pests nor was it unusually hot or dry 2 years ago when this happened. What could have been the problem? Is this something we have to worry about affecting other trees?

A second issue we have is that we have lost 2 large ash trees whose bark was covered with a thin layer of green mold#?). Now, a third ash has the green mold and so do several nearby maples. What is this? What can we do to save these trees? All of these are taller than our house and if we cannot contain this, I fear that another dozen mature maples might be similarly infected. The only trees that seem clear are a small number of saplings. Any advice will be greatly appreciated!

ANSWER: There is really not enough information to be able to determine what killed the oak-sorry. But if it was something that would effect other trees nearby you would have seen signs by now and if they are green it sounds like an isolated death.

The green mold on the trunks of the other trees sounds like 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.  

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.



---------- FOLLOW-UP ----------

QUESTION: I wish I had more information to give on the oak; but, I do not. Meanwhile, if the lichens are not the cause of the ash trees' deaths, then is there a disease that could be hitting only the ash? The 2 that died were very near each other. The one that is now dying back is about 150 feet from the first two. Again, thanks for your help.

Answer
There are several diseases that will infect ash. each have their own signs. Here is a web link to Pest on Ash that lists the diseases. I would suggest you call the Ohio State Forestry agency and ask one of their Foresters to come out and take a look. They should be able to help ID the problem with an on the ground inspection. http://www.forestpests.org/ash/

Contact web page to Ohio Division of Forestry.
http://www.dnr.state.oh.us/Forestry/tabid/5280/Default.aspx