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I have this large tree in my back yard that has about 20% dead branches. The tree is very tall, probably 40+ feet. Most of the branches have this scale on them, and many of the leaves have brown spots. Any idea what this is, or how I can help the tree?

Leaf Branch with scales

  • What part of the world do you live in? Has there been a drought or other change to the area where the tree grows? – kevinsky Aug 16 at 11:31
  • Northern Ohio. No changes to the area. I bought this house about 4 years ago and this tree has always been one of the last to get its leaves in the spring and one of the first to lose them in the fall. – Michael Aug 16 at 21:46
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It looks like fungus . Any wood it is on was likely dead before the fungus started growing. Scale are discrete insects , those I have seen on branches are 3 to 4 mm long and many more scales were on nearby leaves. There may be some lichen with the pictured fungus. Once fungus is in a tree I don't know of any fix. I did have an oak about the size of your tree that that did not completely die until 20 years after the first shelf fungus grew out of the trunk.

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You didn't mention what kind of tree that is. It looks to me like an ash tree, so this answer is based on that. If that's not correct, please provide more information.

That is probably an ash tree (Fraxinus sp.) dying of infestation by emerald ash borer. There aren't actually any signs of emerald ash borer in the photos, but in infested areas it's a reasonable assumption that any visibly unhealthy ash tree is dying of emerald ash borer. The North American species of ash are in the process of going extinct from this invasive insect. In northern Ohio, most of the living adult ash trees you'll see are infested with EAB.

The "scale" is lichen. Heavy lichen cover is a sign of a very unhealthy tree, or at least that that particular branch is very unhealthy. If my assumption of EAB infestation is correct, the lichen and any other issues are secondary problems. The tree is vulnerable to many kinds of secondary issue, because it's already in a weakened state from the EAB infestation.

Expect the tree to die in the next few years. As individual branches die, they will become brittle and prone to falling, especially in windstorms. Falling branches are hazardous. You probably want to cut the tree down to prevent such hazards.

There are preventative treatments for emerald ash borer. It may be too late for your tree, but you can consult a certified Arborist to see if such a treatment can save your tree. If it can, you will need to continue the treatments regularly for the remaining life of the tree.

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  • I'm in northern Ohio and the emerald ash borer is a known pest in this area – Michael Aug 15 at 21:21
  • Not an ash and not damage from an Emerald Ash Borer. The damage from the borer is quite distinctive: bark falling from the tree, dieback of leaves from the TOP of the tree first, with new growth sprouting from the trunk lower down, and D-shaped holes in the bark. Nothing in this picture indicates an EAB infestation. In addition, heavy lichen infestation is NOT a sign of a diseased tree - in fact, it's often as sign of non-polluted air. -1 – Jurp Aug 15 at 22:34
  • @Jurp Please provide some factual statements to support your claim that this is not an ash. The fact that the leaf has only three leaflets does not prove it's not an ash. It's quite common for an ash tree to produce some leaves with fewer than the "typical" number of leaflets for that species. – csk Aug 17 at 16:44
  • @Jurp And the lichen-covered branch in the photo is clearly unhealthy. The bark is visibly cracking and peeling off of the wood. A small amount of lichen may not indicate an issue, but the near-100% coverage by lichen as seen in the photo is not something usually seen on healty trees. – csk Aug 17 at 16:48
  • @csk Ash have five leaflets, not three, and they are not serrated like that shown. See Michael Dirr (any of his publications) for line drawings. I have owned ash trees for at least 10 years, and Fraxinus americana and Fraxinus pensylvanica do not normally produce three-leaflet leaves - not sure why you think that's true. As to the lichen - they only colonize stable "things" (trees, fences, buildings, etc.). Their presence never indicates an unhealthy tree - that the underlying branch may be unhealthy or dead has nothing to do with the lichens on it. – Jurp Aug 18 at 23:13
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I'm pretty sure the white stuff on the bark is a lichen. If so it's harmless to the tree, and is only using the bark as a place to grow.

The leaf brown spots is likely some fungus. Most trees are subject to a bunch of different fungi. In your case, I suspect that it is opportunistic: Your tree is under stress from some other cause.

Add more pictures:

  • A pic of the entire tree.
  • A pic of the bark where it is not covered with lichen/white stuff.
  • A picture of a leaf including it's connection to the twig.
  • A closeup pic of the leaf scar where last year's leaf was attached.
  • Pics of the cross section of the twigs/small branches when cut with sharp pruning shears.

In each picture include an object to give scale. A coin, a tool, a clothes pin (can be attached to twig...)

Ideally pix are taken with a DSLR. You may want to resize them downward for use on this site, and put the original full size images on a public folder on Dropbox or google drive, or equivalent.

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