How Does Sunscald Damage Tree Bark? Causes, Symptoms and Why Temperature Swings Matter

As an Amazon Associate we earn from qualifying purchases.

Sunscald damages tree bark by killing or splitting the outer tissue of the trunk after rapid temperature swings. People asking how does sunscald damage tree bark are usually looking at a split trunk or a strip of dead bark on a young tree and wondering what happened. The damage is tied to temperature more than to light alone. The sources reviewed here describe the same basic mechanism from different state and university extension programs, and they agree on which trunks are most at risk. This explainer covers the cause, the symptoms, the two seasonal forms and the sides of the tree that are usually affected.

Quick answer

Sunscald is linked to death of bark tissue caused by high temperatures, and to rapid temperature fluctuations.
Young, thin-barked trees are the most commonly affected, and the damage is usually on the south or southwest side of the trunk.
Symptoms include split bark on the limbs and trunks and dead brown wood and inner bark.
In severe cases the split can lead to the death of the tree in the following few years.

What sunscald is

Sunscald is a disorder of the bark and trunk. The University of Arkansas extension publication describes it as “Sunscald is a fairly common physiological problem found most commonly on young, thin-barked ornamental and fruit trees.” That wording places the problem in the young tree, where the bark is thinner and offers less protection.

The same publication explains the underlying injury. It describes the damage as “death of bark tissues caused by high temperatures,” and it links the cell death to a specific pattern: “Death of cells in the bark is caused by rapid fluctuations in temperature.” In other words, the trunk is damaged less by heat alone than by the speed at which the temperature changes.

Winter and summer sunscald

The Arkansas publication recognizes two seasonal forms. It notes that “Although we recognize two subcategories of sunscald based on season (winter and summer), both are inherently caused by the same factor.” The two forms share a cause but differ in timing and in the temperatures involved.

For the winter form, the publication offers a sequence that researchers suggest. It states that “Researchers suggest that during the winter, frozen tissue on the south or southwest side of the trunk, which is also being heated by the sun, thaws and then rapidly refreezes.” The repeated thaw and refreeze is the rapid fluctuation that the publication names as the cause of the cell death.

The University of Wisconsin-Extension publication describes the same winter pattern from a different angle. It states that “Rapid temperature changes occurring during sunny but very cold weather in late winter may cause the bark of young trees to loosen and split as tissue expands and contracts.” Here the injury is a split rather than a single area of dead tissue,

The summer form is linked to heat from direct sun. The Arkansas publication describes it as “related to death of bark tissue as a result of lethal temperatures from sun exposure.” The source uses the word lethal for these temperatures.

Which side of the tree is hit

Damage is usually one-sided. The Arkansas publication states that “The problem is common on the lower section of young trunks and the south or southwest side.” The Wisconsin publication gives a close match, stating that “The bark splits on the south or west side of the tree and, in severe cases, can result in death of the tree during the next few years.”

The Arkansas publication links the winter injury to the same side, describing frozen tissue on the south or southwest side that “is also being heated by the sun.” The sources report where the damage occurs, and the sun is named in the source as part of the cause.

Symptoms to look for

The University of Idaho publication lists the visible results. It states that “Sunscald symptoms include split bark on the limbs and trunks and dead brown wood and inner bark.” A split on the south or west side of a trunk may be showing this pattern.

The Wisconsin publication also states that “Field examination is necessary to diagnose sunscald.” The publication does not list other injuries that can look similar, so this article does not offer a comparison.

Why young trees are most at risk

Young trees are the group most often mentioned. The Arkansas publication identifies the problem as most common on “young, thin-barked” trees. The Wisconsin publication uses the same group, noting that the temperature changes “may cause the bark of young trees to loosen and split as tissue expands and contracts.”

This also explains why the risk is highest on the lower trunk of a young tree. The Arkansas publication places the problem on “the lower section of young trunks,” which is the part of the trunk the source names.

How wraps and shading affect the bark

The sources discuss wraps. The Wisconsin publication states that “Wrapping young trees with sisal kraft paper, burlap or other materials in the fall may help prevent sunscald.” It adds that “Reflective materials such as foil have been shown to work even better than paper and burlap wraps to reduce extreme temperature fluctuations.”

The Arkansas publication gives a warning about color. It states that “Black or dark colored tree wrap should not be used” and that dark wraps are unsuitable “because they intensify the temperature problem.” The same publication suggests that “some suggest painting the lower trunk with white latex paint to reflect sunlight.”

The Arkansas publication also states that “Trunk shading materials will need to be left in place for several years until the trunk achieves enough thick, textured bark to buffer the extreme temperatures, or the canopy is wide enough to provide natural shade for the trunk.” That statement ties the protection to a time period, not to a single season.

The Wisconsin publication adds a planting note. It states that “Temperature extremes may also be reduced by planting trees so they lean slightly to the southwest.” This is a site-level measure, and the source does not describe how much lean is needed.

How to read the damage

A pattern on one side of the trunk, a split that runs along the bark, and dead tissue under the bark are the clues that the sources describe. The sources reviewed for this article do not give a timeline for how quickly a split will heal, and they do not describe a repair method for a split trunk, so this article does not offer one.

For related topics on bark and trunk care, see how to water new trees and how to plant bare-root trees in clay soil. Those pages cover different parts of tree care and do not replace the sun-protection points above.

How we chose

The three candidate sources listed for this topic were each checked for an HTTP 200 response on 2026-10-27. Each is a publication from a university extension service. The sources were read for statements about the cause of sunscald, the seasonal forms, the sides of the trunk affected, the symptoms, and the wraps and shading that the publications discuss. Claims in this article are limited to what those fetched texts state. No retail, product or commercial page was used.

What we could not verify

The sources agree on the temperature mechanism, but they do not give a single temperature threshold that applies to every species. The text layer of the Idaho publication was interleaved, so only the symptom sentence could be confirmed verbatim.

What the sources do not say

The sources do not state a temperature at which bark damage begins. They do not describe a repair method for a split trunk. They also do not state how long a split takes to heal, or how many years of shading a specific species needs. The article does not present those figures.

Frequently asked questions

What causes sunscald on a tree?

The Arkansas publication links it to “death of bark tissues caused by high temperatures,” and to “rapid fluctuations in temperature.” The mechanism is the speed of the temperature change, not only the heat.

Is sunscald a disease?

The Arkansas publication calls it “a fairly common physiological problem,” which describes it as a physiological problem.

Which side of a tree gets sunscald?

The south or southwest side is the one named most often. The Wisconsin publication states that “The bark splits on the south or west side of the tree.”

Can sunscald kill a tree?

The Wisconsin publication states that the split can “in severe cases, … result in death of the tree during the next few years.”

Does wrapping a tree prevent sunscald?

The Wisconsin publication states that wrapping “may help prevent sunscald.” It also states that reflective materials “have been shown to work even better than paper and burlap wraps.” The Arkansas publication warns that dark wraps are unsuitable.

Sources

University of Arkansas System Division of Agriculture, FSA6152, “Sunscald on Trees,” James Robbins. https://www.uaex.uada.edu/publications/pdf/FSA_6152.pdf (opened 2026-10-27)
University of Idaho Extension, “Controlling Sunscald on Trees and Vines.” https://objects.lib.uidaho.edu/uiext/uiext30200.pdf (opened 2026-10-27)
University of Wisconsin-Extension, Barron County, “Deciduous Trees Disorder: Miscellaneous Causes of Decline,” G. Kuntz. https://barron.extension.wisc.edu/files/2023/02/Deciduous-Trees-Disorder-Miscellaneous-Causes-of-Decline.pdf (opened 2026-10-27)