Sun scald

also called Sunburn, Sunscald

Bleached, papery patches on fruit and leaves, or cracked, sunken bark on the trunks of young trees after bright winter sun.

Disorder Serious Doesn't spread

What you'll see

Pale, yellow or bleached patches on the sun-facing side of fruit, later turning papery and sunken
Scorched, bleached areas on leaves suddenly exposed to strong sun
On young tree trunks, sunken, cracked or peeling bark on the south-west side
Blistered or corky skin on tomatoes, peppers and apples
Affected fruit tissue often collapses and is invaded by rots

Why it happens

Plant tissue overheats and its cells are killed when strong sun falls directly on fruit, leaves or bark that is not used to it. On tree trunks the damage comes in winter: low afternoon sun warms the south-west-facing bark, which then freezes fast at dusk, splitting the tissue.

Fruit scald follows heat waves, over-zealous leaf removal or a sudden move of pot plants into full sun. Bark scald strikes young, thin-barked trees on bright, cold winter days, especially where trunks are exposed with no shade.

Treating it

Remove badly scalded fruit before it rots
Shade newly exposed or vulnerable plants during the hottest part of the day
Leave damaged bark to callus over on its own rather than cutting into it
Water well so heat-stressed plants can keep themselves cool

Keeping it away

Keep enough leaf cover over ripening fruit rather than stripping leaves hard
Acclimatize pot plants gradually before standing them in full sun
Paint young trunks with dilute white emulsion or wrap them to reflect winter sun
Shade greenhouses in summer and ventilate well to keep temperatures down

Who gets it

Tomatoes, peppers and apples scald on the fruit, while young thin-barked trees such as apples, maples and beech suffer bark damage.