Sunscald on Trees: Cherry, Maple & Fruit Tree Bark

title: "Sunscald on Trees: Bark Cracking on Cherry, Maple, and Fruit Trees"

A long vertical crack in the bark on the south or southwest side of a young cherry or maple tree is a distinctive sight in late winter on Long Island. The bark may be sunken, discolored, or peeling away from the wood. The tree looks like something severe happened to it. Something did — but not what most gardeners assume.

Sunscald is a specific winter injury to tree bark caused by rapid temperature fluctuations on sun-exposed surfaces. It is not a disease and cannot be treated with fungicide. The right response is to protect trees in advance and manage wounds correctly after damage occurs.

The mechanism: freeze-thaw injury to bark

Per Missouri Botanical Garden, sunscald occurs when "the cells in the bark and cambium on the south or southwest side of the trunk are warmed by direct winter sunlight, become active, and then are killed when temperatures drop rapidly after sunset." The activated cells lose their cold-hardening and are killed by refreezing.

The result is a dead patch of cambium — the thin layer between bark and wood that contains the tree's growth cells. When the cambium is killed, the overlying bark dies and eventually loosens or falls off. The exposed wood may darken and crack.

Per NC State Extension, sunscald is most common on fruit trees, thin-barked ornamentals, and trees recently moved from a shaded nursery environment to full sun exposure. First-year transplants are at highest risk. Established trees with thick, rough bark are largely immune.

A related injury, frost cracks, is also caused by temperature extremes. Per Missouri Botanical Garden, frost cracks are long vertical splits caused by the rapid contraction of wood during sudden temperature drops, not specifically sun exposure. They often follow the same radial cracks each year, opening in winter and partially closing in summer.