The short version: Sunscald is bleached, papery white or tan patches on the sunny side of a leaf or fruit. It follows a seedling going outside too fast or a heatwave, is not a disease and does not spread. Harden seedlings off, shade them on hot afternoons, water deeply, and leave scorched leaves on until new growth replaces them.
Scald or disease?
Scald sits where the sun hits: the top leaves, the north and west sides of the plant, and the shoulder of a tomato or capsicum that lost its leaf cover. The patch is pale, dry and papery, and the shaded leaves underneath are clean. It appears within a day or two of a hot spell or a move outdoors and worsens only while the exposure continues. Disease behaves differently: spots on shaded leaves as well as sunny ones, rings or yellow haloes, a fuzzy or powdery coat, and new spots day after day. Dry patches on the sunny side with clean new growth make scald the likely cause, though spray drift and hot wind also mark one side, so think back over the week.
Cut a small dry patch from otherwise sound fruit and eat it soon, since the dead skin lets rot in. Throw out any fruit gone soft or mouldy.
The fixes
- Harden off. Seedlings raised under cover have thin, soft leaves. Start them out of the wind with an hour or two of morning sun, add an hour a day for a week to ten days, and slow down if they wilt.
- Afternoon shade. On days forecast over about 35 degrees, and on any bright day for seedlings still hardening off, rig 30 to 50 per cent shade cloth above and west of the plants, clear of the leaves, or stand a chair there. Take it down when the heat passes; morning sun is welcome.
- Water deeply before heat. A wilted leaf scorches far faster than a well-watered one. Water deeply the day before a hot spell, top up early that morning, and mulch to hold it.
- Keep the leaves on fruiting plants. Hard summer pruning bares tomato and capsicum fruit; leave the leaf cover above a truss.
- Leave scorched leaves alone until new growth has taken over and the hot weather has passed, then trim the fully brown ones. It still shades what is below.
What it will not do
Scald does not spread to other plants, and fertiliser does not fix it. Bleached patches do not green up again, so judge recovery by new growth: a plant with scorched outer leaves and a green heart puts out fresh leaves and carries on. A seedling that has lost every leaf may not, so harden off properly.
White patches after a hot day are a plant catching up with its new address, not a plant giving up.
Related reading
Raise the next batch from the vegetable seeds collection.