Field Identification
Sunscald is tissue death on fruit, leaves, or bark caused by intense solar radiation, especially after sudden exposure of previously shaded surfaces. Apples and peppers show bleached or papery patches; young tree bark can crack on the southwest side. It spikes after heat waves, reflective mulches, or aggressive summer pruning that removes protective canopy. It is abiotic -- no insecticide fixes radiation physics.
Check whether damage faces the afternoon sun and follows a sharp line between shaded and exposed tissue. Compare with disease lesions that often show sporulation or irregular margins. On trunks, look for southwest orientation and link events to recent pruning or transplanting that removed shade. Fruit damage is usually on the upper shoulder facing sky.
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How to Deal With It
Organic Control Methods
Healthy bark microbiome recovers faster after mild sunscald when cambium is not fully killed. Vigor from good root systems supports callus formation. These are indirect -- they do not replace shade or paint when cambium is cooking.
Whitewash or use tree guards on thin-barked species after planting or sudden exposure. Shade cloth over high-value fruit during heat spikes reduces shoulder burn. Avoid laying reflective silver mulch up to stems of peppers and tomatoes without stem shields. Harden transplants gradually instead of moving from dense shade to full sun in one day.
Prune conservatively in summer when removing large limbs would expose vertical bark to new sun angles. Train fruit clusters so apples do not press against hot metal stakes. Orient rows where crop-specific guides suggest lower afternoon exposure if your site allows.
Use paper trunk wraps in winter-sunscald zones on young trees -- remove in spring before girdling insects hide under them. Move container plants a few feet into dappled shade during record heat if feasible. Row cover with hoops can diffuse light on tender transplants.
Kaolin clay particle films on fruit reflect sunlight and reduce sunscald on some crops when applied before heat events per label. Calcium sprays do not fix sunscald. Do not rely on foliar oils during heat -- they can increase damage. Focus on physical shading and orientation first.
Let Nature Handle It
Natural Enemies
- Beneficial Fungi
- Competitive Microbes
- Antagonistic Bacteria