Let it Grow: Dead branches do not mean your tree is in trouble
Jen asked: I have a lot of dead branches on the inner part of my ash tree. Is this a sign that it has Emerald Ash Borer or something else that causing the tree to die? Does it help the tree to remove the dead branches?
The answer is no. Dead branches on the inner canopy of an ash tree is not a symptom that would be caused by Emerald Ash borer (EAB). EAB causes trees to decline because they feed on the vascular tissue and restrict water movement in the tree. Damage to the vascular system causes wilting and branch dieback in the tops of the trees or at branch tips inward. Top-down dieback is an indication that something serious is wrong with a tree.
The inner branches of all trees will decline and die as the tree matures. While there are sometimes secondary diseases or insects that contribute to the decline of inner branches, the primary cause is directly related to tree physiology. When inner branches are shaded by new growth on the outer canopy their ability to carry out photosynthesis is reduced.
In addition, less water and dissolved nutrients get to the branches because they lose less moisture when shaded and protected from wind. As a result, the outer canopy draws more water, dissolved nutrients and sugars than the inner canopy.
Eventually the inner branches decline because they are unable to produce enough food and to draw enough nutrients to support themselves. As this occurs, the upper portion of the tree will actually draw the remaining resources from the branch and start to seal it off at the branch collar to gradually close off the wound when the branch dies and eventually sloughs out. Trees do not have a method to pump food and nutrients into branches that cannot support themselves. In fact, this would be very counterproductive for the tree.
Do these dead branches need to be pruned out? In most cases pruning deadwood from the inner canopy does not benefit the tree. The exception is when there is a secondary disease or insect involved that may progress further if left in the tree. In urban areas, however, many find it desirable to have deadwood pruned out for aesthetic reasons or to reduce the risk of dead branches falling on people or personal property. Having the deadwood pruned out also reduces the amount of branches that need to be cleaned up from the ground on an ongoing basis.
Brian asked: Is treating for Emerald Ash borer effective and is it a one-time treatment?
EAB treatments have proven to be very effective for saving trees from EAB. Trees need to be treated every year or every other year, depending on the chemical that is used, for as long as a homeowner wants to keep the tree protected.
Thanks for these questions. You can send me tree, shrub or lawn questions and I will respond directly to all of them and include the more common questions in future columns.