Tree Dieback

This summer drought has been tough on many plants, trees included. Some trees have shown significant decline and die back (bare branches at the top or one side). However, there are multiple reasons for decline of trees beyond drought. Exploring those reasons can help diagnose the problem, hence develop a potential solution.

Branch die back can occur gradually over time or can occur suddenly, depending on the cause. It can occur on well-established older trees or on young, newly planted trees. Regardless of the circumstances, it is never a welcome site to a homeowner.

One common and widely misunderstood cause of die back is a tree that was improperly planted. The die back may take years to surface, and if that occurs, it is too late to correct the problem. Trees must be planted with the root flare (where the root meets the trunk) above the soil line. The root flare can be identified by a swelling or a flaring out at the base of the trunk.

Continuing with root problems, any damage to the root zone by heavy equipment driving over the area will inhibit the ability to take up water and nutrients. This will ultimately cause dieback and potentially be fatal to the tree. In addition, compaction in the root zone area by building retaining walls, piling building materials, heavy traffic, adding or removing soil, or any other option will cause the same effect. The only way to prevent this cause of die back is to avoid the traffic and other compaction causes.

Both drought and wet soil conditions can cause decline to a tree. Young trees are particularly susceptible to drought conditions and should be provided supplemental water for the first five years. On the other hand, if the soil is too wet, all of the pores underground are filled with water and the tree is deprived of oxygen, leading to a root system unable to support a healthy tree. Make necessary soil grading changes to improve drainage before planting the trees. There are some species of trees that can tolerate wetter conditions. Choose the right plant for the right place.

Anything that causes damage to the vascular system of the tree will inhibit the ability of water and nutrients to flow from the roots to the rest of the tree. This will include damaged bark from insects, animals (including rabbits, mice, and deer), weed trimmers, lawn mowers, ropes, or wraps. The tree cannot heal itself from this damage and wound sealants or wraps are largely ineffective. The best preventative measure is avoiding the damage from the start. Keep damaging tools away from the tree and place physical barriers around them to protect them from animals.

There are some diseases and insects that will also damage the vascular system of a tree. Verticillium wilt, oak wilt, and pine wilt are vascular diseases that often initially present themselves by causing one part of the tree to die back.

There are borers (like emerald ash borer) that attack trees, feeding on the water and nutrient conduction tissue, causing die back. Because these borers can cause symptoms similar to those created by other causes, it is important to accurately identify the cause before deciding on a course of action.  

Trees are an important part of the landscape and deserve the best care given to them. Just a bit of routine maintenance can make them live for decades.

Carol Shirk

Certified Master Gardener