Ash Decline Disease Looks Like Drought

Q. I think I have an ash tree. I've been reading about ash tree decline disease with some apprehension. I noticed my tree has bark with damp spots and it's starting to separate from the trunk. Is this a sign of ash tree decline or something else?

As you can see, ash decline looks exactly like the tree is not getting enough water. This is because the disease plugs up the tubes carrying water from the roots to the tops.

A. Probably not. Ash decline starts as dieback of the limbs from the outside, higher up on the tree. A common problem on many ash trees is sunscald or severe sunburn of the trunk and limbs in full sunlight.

            In our climate, sunlight is very intense and will “sunburn” exposed surfaces of some trees. These exposed surfaces can be the trunk, limbs and even the unprotected fruit of some fruit trees. Most of this sort of damage is seen on the West or South sides of tree trunks or on the upper surfaces of large limbs.

            We see this most often on trees that have thin bark covering the trunk and limbs such as some ash trees, locust and honeylocust, and many fruit trees. We don’t see it as often on trees with thick bark covering the trunk and limbs such as pine trees.

            It can be important to leave small stems growing from the trunk and limbs so they provide shade to help prevent damage from intense sunlight. Remove these small limbs when they get bigger than pencil-sized in diameter.

            Scientists don’t agree if these sunburned areas attract boring insects or not. It’s a “chicken and egg” kind of thing; did sunscald attract the borers or borers contribute to the sunscald? Regardless, oftentimes borers are found damaging the tree near these areas.

            It will not hurt the tree to remove the dead surface of the trunk or limb for a closer inspection. Either pull the loose bark from this area or cut it away with a clean knife. Inspect these areas for borer damage. Removing this dead surface area with a sharp knife helps the trunk or limbs heal more quickly. Make sure the tree is getting enough water at each watering and correct an irrigation problem if one is found.

             If you see some borer activity in fresh wood in the sunburned area, the tree will probably recover unless the damage is severe. Get the tree healthy and let it heal on its own.