Why Are My Tree Branches Dying? Getting to the Root of Branch Dieback

I often have clients contact me because branches on their trees are dying. Their assumption is that something going on directly in the branches is causing the dieback. While that can certainly be the case, there are also a myriad of other reasons why tree branches can die.

Below is a breakdown of what I commonly see causing branch dieback in the UW-Madison Plant Disease Diagnostics Clinic.

What is dieback disease in trees?

Though many homeowners refer to progressive branch death as “dieback disease,” it is not actually a single specific illness. Instead, branch dieback is a symptom characterized by the progressive dying of tree branches from the outer tips inward.

It is typically caused by either an infectious disease (like cankers, vascular wilts, or root rots) or severe environmental and insect stress (like girdling roots, winter burn, flooding, or wood-boring beetles). Identifying whether the underlying issue is structural, environmental, or pathogenic is the first step to saving the tree.

Common Tree Disease Causes of Branch Dieback

Canker Diseases

Canker pathogens (most commonly fungi and bacteria) locally infect areas on individual branches. Eventually, they girdle the branches, cutting off nutrients and leading to branch death.

• Symptoms: Often, the dead branches are scattered randomly in an affected tree.
• Management: These types of diseases are most commonly managed by pruning out the diseased branches to keep the pathogens from moving into the main trunk, where they can cause more extensive damage.
• Common Examples: Nectria canker (caused by a fungus that can infect a wide range of woody plants), golden canker (caused by a fungus that is relatively specific to pagoda dogwood), and fire blight (caused by a bacterium that infects a wide range of woody rosaceous hosts, but has its biggest impact on apple, crabapple and pear trees).

Vascular Wilt Diseases

For woody plant species, vascular wilt diseases are typically fungal in nature. The pathogens find their way into a plant’s xylem (the water-conducting tissue) through direct infection (typically via roots) or via insect feeding or egg laying activities. Vascular pathogens eventually lead to blockages in the xylem that limit water movement to branches. This lack of water is what leads to branch dieback.

• Symptoms: Dieback typically starts with a single branch and progresses to encompass a cluster of branches. Often vascular wilt diseases eventually kill trees.
• Common Examples: The most common vascular wilt diseases are oak wilt, Dutch elm disease, and Verticillium wilt.
• Management: Once infection occurs, these diseases are challenging to manage. Management typically involves using preventative fungicide injections (for oak wilt and Dutch elm disease) or avoiding planting susceptible tree species in areas where the pathogen is known to occur in the soil (for Verticillium wilt).

Root Rots

Root rots tend to be more of an issue in sites with heavier soils and poor drainage, as well as in years with above average rainfalls. These wetter conditions are favorable for soil-borne fungi and water molds (in particular Phytophthora) to infect roots.

• Symptoms: Infections lead to deterioration of roots, which in turn leads to reduced ability of the affected plants to take up water, resulting in leaf thinning and branch dieback across a broad section of the upper tree canopy.
• Management: Modifying soils to improve drain prior to planting and use of fungicide treatments (if root rots are detected early) can be useful management strategies. Fungicide use, however, requires proper diagnosis of the causal organism(s), as root rot fungicides are somewhat specific in terms of the organisms that they control.

Other Root Diseases

The primary disease that I see in this category is Armillaria root disease. The fungus involved tends to infect through wounded roots (often from construction damage or trenching the severs root grafts) and colonizes roots and the lower trunks of trees.

• Symptoms: This colonization inhibits water uptake and also disrupts water transport in the trunk. Trees with Armillaria root disease often survive for a period of time, but symptoms like branch dieback intensify when trees are stressed (e.g., during a droughty growing season). Eventually infected trees succumb to the disease.
• Signs to Look For: Spore-producing mushrooms and rhizomorphs (root-like fungal structures that grow through the soil) help the fungus spread from tree to tree.
• Management: Once trees are infected, there is no cure. Removal of infected trees, including stumps and root systems, is the only management choice to eliminate the pathogen’s food source and protect nearby trees.

Fungal Wood Rots

These diseases are less common causes of branch dieback, but can contribute on occasion. The fungi involved often enter through external wounds, leading to the rot of interior wood in tree branches and trunks.

• Symptoms: In the process of rotting internal wood, they can sometimes disrupt the xylem around the point of infection, killing branches fed water by this compromised vascular tissue.
• Signs to Look For: Look for fungal conks (shelf fungi) or mushrooms growing directly out of wounds on the branches or trunk.
• Management: Unfortunately, once infection occurs, there is no treatment. So, management relies on preventing the mechanical wounding that provides entry points for these pathogens.

Non-Disease Causes of Branch Dieback

Often, branch dieback is not caused by disease, but rather environmental stress or pest activity.

Girdling Roots

These are roots that encircle the base of a tree trunk rather than growing outward. They most commonly form when trees are planted improperly or left too long in plastic nursery pots. Girdling roots eventually come into contact with the trunk of a tree and compress the vascular tissue under the bark. This limits water flow, and any branches fed by this compressed vasculature can decline and eventually die.

Winter Burn

This type of dieback most commonly occurs on evergreens (yews and boxwoods can be particularly hard hit) and is really a problem with dehydration in affected trees and shrubs over the winter. Proper watering, particularly late into the fall, can help prevent winter burn from being an issue.

Saturated Soils & Flooding

Flooding of soils for an extended period purges oxygen from the spaces between soil particles. Without this oxygen, plant roots die, leading to reduced water uptake, subsequent branch dieback, and often tree death.

I personally killed a dappled willow this way years ago. When I planted the shrub, I wanted to make sure it received sufficient water. So, I set up a soaker hose and turned it on. I then neglected to turn the water off for 18 hours, leading to a small bog in my yard in the area around the shrub. The soil was totally saturated and went anaerobic, and the willow died shortly thereafter.

Insect Infestations

Many insects can lead to branch dieback, but the most common one I see is the two-lined chestnut borer. I often get requests to test dying oak branches for oak wilt, only to discover that the branch dieback is actually due to this opportunistic beetle. This insect and many others that can cause branch dieback are attracted to stressed trees, so reducing tree stress can prevent them from being a problem.

Need Help Diagnosing Your Tree?

As you can see, diagnosing the cause of branch dieback in trees and shrubs can be a complex process. In many cases, there may be multiple overlapping causes of dieback in a given plant.

But that’s why the UW Plant Disease Diagnostics Clinic (PDDC) and Insect Diagnostic Lab (helmed by PJ Liesch) are always available to help you find answers. Feel free to tap into our expertise whenever you have plant disease or insect questions.

Contact the Experts

You can reach me at (608) 262-2863 or pddc@wisc.edu, and PJ at (608) 262-6510 or pliesch@wisc.edu. Also, for additional information on many of the diseases/disorders discussed in this article, check out the fact sheets and web articles on the PDDC website (https://pddc.wisc.edu/). For updates on new PDDC educational materials and training opportunities, you can follow the clinic on Facebook or Twitter (@UWPDDC) or subscribe to the clinic’s email listserv by sending a subscription request to pddc@wisc.edu.

Get Local Tree Care

If you’d like to leave the diagnosing to the professionals and simply get assistance caring for your trees, Wachtel Tree Science is here to help. We provide local services like pruning, preventative treatments, and more throughout Southeastern Wisconsin. You can contact the team to get more information or request a quote.

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