Whitewash Fruit Protectant: Looks good, but does it work?

Gene Miyao, Farm Advisor, Yolo/Solano/Sacramento Counties

The principle of using a white reflective coating to protect exposed tomato fruit has merit. On those 105°F summer days, clearly your personal outdoor experience between wearing a dark-colored or a white polo shirt is a simple experiment that provides compelling logic to whitewash those tomatoes.

Simple measurements of internal fruit temperature show that whitewash does reduce fruit temperature by several degrees. However, the question remains. What is the maximum temperature and conditions before fruit begin to sunburn and sunscald?

While I do not know the answer, the temperature threshold question remains important. Temperature is not the only controlling factor, but is a primary one. Although it may seem like a contradiction in proper management decision making, the following holds true. The higher the temperature, the more likely whitewash will fail to protect fruit. Why? Because whitewash is only an aid, not a temperature insulator. Whitewash is not a canopy replacement should vines collapse.

Fruit temperature measurements I’ve taken demonstrate that even a dead leaflet provides more protection to a fruit than 300 lbs. per acre of whitewash. So, establishing and maintaining a canopy is far superior to a whitewash application for thermal protection of the fruit. With few exceptions, in numerous replicated tests conducted in grower fields, yields were not improved with whitewash at rates up to 300 lbs. per acre.

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