Sunburn & Sunscald
Just like us, trees can suffer lasting damage from exposure to the sun and intense heat. Sunburn affects leaves, with discoloration and damage showing after sudden or intense exposure. Sunscald is a sun-induced injury to the bark—usually on the south or southwest side of young, thin-barked trunks. Species often afflicted include: maples (Japanese, red, and hybrids), ash, honeylocust, sweetgum, red oaks, pecans, elms, hollies, and magnolias.
Both sunburn and sunscald are caused by exposure to intense light and heat. Changes in the landscape, such as limb loss or tree removals, can abruptly increase sun on parts of a tree that were previously shaded. The heat may be further intensified and reflected by nearby walls or pavement. Exposed to extreme heat and lacking insulation, the bark of young or thin-barked trees may die and later slough off.
Symptoms of Sunburn & Sunscald
Foliage (sunburn): Affected leaves first look washed-out or bleached, then redden. Overlapping leaves can make distinct “shadow” patterns.
The sunburn may looking patchy in the canopy due to the changing light conditions throughout the day. Foliar sunburn frequently follows the path of the sun. For the same reason, sunburn is found most often in the south or southwest side of the landscape.
Bark (sunscald): The early signs of sunscald are subtle: discolored bark and small vertical cracks. Bleeding may appear in the spring. Later, long vertical fissures form as dead bark peels away. Large wounds weaken the trunk and can contribute to future failure.
Prevention
The best way to prevent long-term sun damage to your trees is to improve the environmental conditions and cultural practices of your landscape. These measures are intended to reduce stress and avoid aggravating injuries.
- Leave adequate lower branches on newly planted trees for a few years to shade the trunk.
- Limit drastic canopy thinning.
- Where possible, provide shade from the south/west with nearby plantings or a light-colored board/fence.
- Reduce reflected heat from hardscape.
- Keep trees evenly watered during prolonged heat/drought
- Maintain a 2–4 in. organic mulch ring (not piled on the trunk).
Management
Sunscald (on the trunk)
Sunscald may be managed with trunk wraps. Use light-colored wraps, such as kraft paper or breathable white fabric. Do not use dark materials; they intensify heating. Wrap without constricting the trunk, especially where it flares out near the base. Leave shading materials in place until the bark thickens or the canopy shades the trunk.
Some practitioners use diluted white latex paint on lower trunks to reflect sunlight. We don’t recommend this as it can be difficult to make sure your paint is plant-safe.
If damage has already occurred, watch the afflicted area over time—large, long fissures indicate structural weakness and may justify risk assessment or support.
Sunburn (on the leaves)
Proper irrigation and mulching can help the tree cope with extreme heat. Avoid fertilizing in hot periods, as this will stimulate tender growth which is ill-equipped to contend with extreme heat. For high-value plants, short-term shade cloth can limit sunburn during extreme heat, although it is visually obtrusive.
