Greenish/black patches have appeared on many of the trunks of several ash...

Asked January 30, 2014, 11:09 AM EST

Greenish/black patches have appeared on many of the trunks of several ash clumps in my garden. The trunks are mature and stand about 30ft high. Looking closely the patches are made up of small black dots. Is this something I need to be wary of? and what is it?. Is it treatable?

Outside United States forestry trees and shrubs tree health plant pathology

4 Responses

Hi, I would be glad to help with your tree question, but I need to find out some more information from you. The attached photo shows what appears to be extensive fissure cracks and cankers in the bark. It also appears this specimen is multi-stemmed. Can you tell me what county, state or country where this tree is growing and if there are existing signs of internal decay and decline. I would suspect this is a fungal problem and it may be from an internal reason or an environmental situation. Also wondering if you have noticed signs of Emerald Ash Borer ... has this insect been discovered near your home ... if so, you need to immediately contact your local forest health specialist for a 'site visit'. ~DOT (2-4-14)

Hello Dot, thank you for answering my question.

I am located in the United Kingdom and live on the Isle of Wight, four miles off the south coast near the port of Southampton. It is a semi rural area and the trees are located in my garden which comprises of about an acre.

The trees are multi stemmed and as far as I can tell there are no obvious signs of internal decay or decline or beetle infestation. Last summer was particularly dry and I didn't notice any marks on the trees before the end of last year.

I last coppiced these trees about twenty years ago.

I'm not aware of my area having Emerald Ash Borer, however, there has been a lot of talk about Ash Dieback disease. Having studied pictures of that it doesn't seem to fit my particular problem.

I have included a long shot of the trees so you can get a better idea of their location.

Thank you,
Keith Clatworthy

I am hesitant to reply because I do not have direct experience with the trees or fungi of the UK. But with that caveat, this looks a lot to me like sooty mold, a mostly harmless surface fungus common to trees and plants. Sooty mold more often grows on leaves and branches, and its growth can be stimulated by the deposition of sugary "honeydew" by aphids feeding above those leaves or branches. Here's a link to a bit more information on sooty mold (disregard the "Armillaria root rot" title, that appears to be an error, as well as a somewhat more detailed article on aphids on trees and shrubs. Both are from the University of Minnesota Extension, so again should be taken cautiously as conditions may be different in the UK.

Whether or not this is actually sooty mold, in general I would not be concerned about major damage to the tree. Surface fungi rarely cause systemic or structural damage; their effects tend to be more cosmetic than catastrophic.

Hope this helps.
-eli