Don’t forget sunscreen: Protecting tree fruits during extreme heat events

Research Brief Publication Date: May 07, 2024
Last Updated: May 07, 2024

Kirsten D. Hannam and Jesse L. MacDonald


As part of developing a “climate resilience toolbox” for Canadian tree fruit, this study evaluated the effect of a locally produced, calcium carbonate-based foliar protectant on apple sunburn and water stress.

Canadian tree fruit producers need tools to help improve the resiliency of their crops to extreme weather events, such as heat waves. The use of sprayable foliar protectants as a “sunscreen” to protect fruit from sunburn and reduce water stress have been explored extensively in the United States but not in Canada. 

Foliar protectants are particularly appealing because they are inexpensive to purchase and easily applied using commonly available spray equipment. They work by blocking, reflecting, and/or scattering the sun’s rays and thus reducing fruit and leaf temperatures. This study was initiated just as the 2021 heat wave hit the province, providing a unique opportunity to test the efficacy of the foliar protectant for maintaining fruit quality under extreme heat conditions.

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Apple tree. Photo by Jamil Rhajiak.

About this Brief

This brief was prepared by the BC Food Web team with the help of Kirsten Hannam and Jesse MacDonald, and is based on the following scientific journal article:

Hannam, K. D., & MacDonald, J. L. (2023). Tools for climate resilience in tree fruit II: a calcium carbonate-based foliar spray showed potential for protecting fruit quality during an unprecedented heat event. Canadian Journal of Plant Science, 103(2), 228-232. 


Key Findings

  • Intense and prolonged heat can cause widespread losses in tree fruit crops, and is only going to become more pronounced with climate change. 
  • A foliar protectant is a product that is sprayed on leaves to protect crops from sun damage and heat stress. They are inexpensive and easily applied with existing farm machinery. 
  • The foliar protectant reduced the occurrence and severity of sunburn damage in apples, making it a promising tool for climate resilience in Canadian tree fruit. However, more research needs to be done to determine the best time, frequency, and concentration for application.