sunburn / leaf scorch

Symptoms

Bleached papery patches between leaf veins on the side facing the sun, crispy brown leaf margins, no fungal or pest signs, damage appears within hours of strong sun exposure.

Easily confused with

• drought stress

  How to tell them apart: Drought stress on Japanese maple shows up first on the OLDEST, innermost and lower leaves and progresses uniformly across the whole canopy regardless of light exposure. Scorch begins at the leaf margins and the area between veins, turning the tissue tan to pale brown, papery and brittle, with the whole leaf often curling inward and wilting before it browns. The damage follows the watering pattern (worse during dry spells, on the windward side, or on root-restricted plants) and the soil is dry several centimetres down. Sunburn, by contrast, is confined to the leaves and leaf-parts that face the strongest afternoon sun (south/west-facing, top of the canopy, exposed outer edges), often leaving shaded interior leaves perfectly green. Sunburn scorch is sharply localised, frequently a bleached silvery-white or reddish-bronze patch on the upper, sun-struck surface before turning brown, with a clear boundary where shade begins and no general wilting.

• olive Verticillium wilt

  How to tell them apart: On Acer palmatum, abiotic sunburn produces uniform marginal and interveinal browning with crispy, papery tan-to-brown leaf edges, distributed evenly on the most sun- and wind-exposed outer canopy, with no wilting of green tissue and no discolouration in the wood. Verticillium dahliae instead causes sudden one-sided wilting and leaf scorch confined to a single branch or sector of the crown, where leaves curl and collapse while still partly green, and peeling the bark of an affected limb reveals tell-tale olive-green to grey-brown streaking in the sapwood. The clinching sign is this internal vascular staining and the branch-by-branch (sectorial) dieback of Verticillium versus the even, surface-only, exposure-driven scorch of sunburn.

• overwatering / waterlogging

  How to tell them apart: Overwatering and sunburn (sun scorch) on a bird's nest fern (Asplenium nidus) both produce browning, but they sit in different places and feel different. Overwatering browns the centre and base of the rosette first: the frond bases turn soft, dark brown and mushy, the crown may smell sour, the potting mix stays wet, and lower/inner fronds yellow then collapse limp. Sunburn instead bleaches the most light-exposed upper or outward-facing fronds: it starts as pale yellow-white patches that dry to crispy tan-brown with a papery texture, the affected zones face the light source, and the soil and crown are firm and healthy. Rule of thumb: wet, soft, mushy and central means too much water; dry, crisp, bleached and on the sun side means too much light.

• alkaline-soil chlorosis

  How to tell them apart: On Hydrangea macrophylla, alkaline-soil chlorosis shows uniform pale-yellow interveinal tissue with a crisp green vein network, appearing FIRST and worst on the YOUNGEST leaves at the shoot tips, evenly over the whole canopy regardless of which way the leaf faces, with the leaf staying soft and flat. Sunburn / leaf scorch instead shows bleached whitish-to-tan papery patches only on the SUN-FACING side of EXPOSED upper and outer leaves (shaded and inner leaves are untouched), the damaged tissue feels dry, brittle and crispy and the leaf MARGINS turn brown and curl, and it can appear within hours of an intense sunny spell rather than developing slowly. Quick test: yellowing newest leaves all over = iron/manganese lock-up (chlorosis); bleached brittle patches with brown crisp edges on the sunny outer leaves only = sunburn. Both are abiotic with no spots, mould, webbing or insects.

• hydrangea leaf spot

  How to tell them apart: Sunburn (leaf scorch) and Cercospora hydrangeae (hydrangea leaf spot) both leave brown dead patches on Hydrangea macrophylla, but sunburn shows NO discrete spots: it bleaches whole interveinal zones to pale tan/papery, only on the upper, sun-facing side of exposed leaves, with crispy brown margins, and it appears suddenly within hours of intense sun or after a shaded plant is moved into full sun. Cercospora instead produces many small, discrete, round-to-angular purple-brown spots, each with a distinctly paler tan-to-grey centre (sometimes a thin dark ring), starting on the oldest lower and inner leaves and worsening in warm, humid, splash-wet weather. Look for the dot pattern with pale centres and a uniform spread across shaded and sunlit leaves alike: that is Cercospora; a uniform bleached scorch confined to the most sun-exposed leaf faces with no individual spots is sunburn.