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WSU Decision Aid System Update July 2024

Written by Liesl Oeller, Washington State University, July 8, 2024

DAS Sunburn Model

A heat wave and intense sun is impacting much of Washington and Oregon, and apple sunburn risk is high. Check the DAS sunburn model for apples to assess risk in your area this summer.

Information about conditions and management and image of a data table
Apple sunburn risk at the Wenatchee station.

There are different types of sunburn in apples: sunburn browning, photooxidative sunburn, and sunburn necrosis. 

three apples with three types of sun damage
Symptoms of sunburn necrosis, sunburn browning, and photooxidative sunburn in apples.

Sunburn Browning

Sunburn browning is the most prevalent type of sunburn, and it is caused by high fruit surface temperatures and ultraviolet radiation. Sunburn browning usually occurs during the afternoon on fruits acclimated to high light (i.e. previously exposed to sunlight for several days before the sunburn event). However, sunburn browning symptoms may not appear for a few days after the sunburn event occurs. Internal fruit quality of apples with sunburn browning is affected and declines further during cold storage. This is another reason to protect your apples from sunburn.

Photooxidative Sunburn

Photooxidative sunburn occurs in apples that have been shaded prior to sudden exposure to full sun (e.g. apples exposed during thinning or pruning, or when a limb shifts with heavy crop load). This sunburn type is independent of temperature, and is caused by visible light. The first symptom of photooxidative sunburn is whitening of the sun-exposed side. Later necrosis may form on these apples in the center of the bleached area.

Sunburn Necrosis

Sunburn necrosis results from thermal death that occurs at a fruit surface temperature of ~126 °F. If no protective practices are used, Washington State apple growers lose about 10%, on average, of their crop to sunburn cullage.

Read the full article about different types of apple sunburn on the DAS website!

Subscribe to DAS

Now is the perfect time to subscribe to DAS! Keep track of pest emergence and see management options as the season progresses. You can use our time machine tool to look back on weather data from the last five years, and see how 2024 compares. You can also set up alerts to remind you when key pests are emerging for timely management.

For weekly updates on DAS models and tools, subscribe to our mailing list. Now is the perfect time to subscribe to weather stations on DAS, get started today!


Liesl Oeller
Liesl Oeller
Washington State University
(509) 335-5815


Fruit Matters articles may only be republished with prior author permission © Washington State University. Reprint articles with permission must include: Originally published by Washington State Tree Fruit Extension Fruit Matters at and a link to the original article.

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