Sunscald occurs when the fruit of a plant is exposed to the direct rays of the sun during hot weather. It is more apparent in plants that have sparse foliage or those that may have previously lost a good deal of leaves to a leaf-defoliating disease. Sunscald is especially prevalent on previously shaded plant parts that have been suddenly exposed to the sun. The damaged areas are vulnerable to attack by insects, fungi, and bacteria.

The most frequent victims of sunscald include tomatoes, peppers, apples, grapes, strawberries, blackberries, and raspberries. Other fruits can be affected but are not commonly observed.

Symptoms and Diagnosis

Sunscald is most prevalent on the unripe fruit. White or yellow blisters will develop on the sides of the fruit that are facing the sun. With continued exposure to the sun, the damaged areas may become papery, flattened, and grayish-white. Black mold may grow in the papery patch and cause the fruit to rot.

Integrated Pest Management Strategies

1. Maintain healthy plants with plenty of foliage. Water tomatoes thoroughly on a regular basis. Fertilize with a low nitrogen or slow-release fertilizer at planting and at full blossom. Mulch lightly when the soil has warmed.

2. Cover exposed fruit with a lightweight material, such as shade cloth, in order to provide them with some shelter from intense sunlight.

3. Practice controls for leaf diseases in order to prevent defoliation that leaves the fruits more vulnerable to sunscald. These practices may include crop rotation, proper sanitation, and the use of fungicides.

4. Plant varieties that are tolerant to disease. Select varieties that tolerate Septoria leaf spot and early blight, two of the most common defoliating diseases.

Organic Strategies

Strategies 2 and 4 are strictly organic approaches. Using an appropriate organic fertilizer would be a viable organic approach to Strategy 1. Of the options mentioned in Strategy 2, consult the Organic Materials Review Institute (OMRI™) for appropriate organic copper products.