According to a Washington State University (WSU) study, climate change is posing significant challenges to some of the most important apple-growing regions in the United States.

WSU Insider reported that a group of researchers analyzed more than 40 years of climatic conditions (1979–2022) affecting the growth cycle of apple trees, from bud break and flowering to fruit development, ripening, and color formation.

Although many growing areas are facing increased climate risks, three regions are most affected: Yakima, Washington; Kent, Michigan; and Wayne, New York.

“We shouldn't take for granted the delicious apples we love to eat so much,” said Deepti Singh, WSU climatologist and study author.

“Changing weather conditions throughout multiple parts of the growing season pose potentially compounding threats to apple production and quality. Going forward, it would be useful to think about adaptations at different stages of apple growth that can minimize overall detrimental impacts,” Singh commented in statements reported by WSU Insider.

Specifically, the researchers examined six parameters that influence apple growth, including two extremes: extremely hot days (above 34°C), which can cause sunburn and other issues, and warm nights (above 15°C), which can negatively affect apple coloration.

Other factors considered were the number of cold days, the “cold portions” (or the number of coldest hours an apple tree requires for dormancy), the last day of spring frost, and growing degree days, meaning the number of days above a certain temperature conducive to apple growth.

Changes in these parameters can disrupt apple production by altering bloom timing, increasing the risk of sunburn, and affecting apple appearance and quality.

The challenges are complex, partly because apple trees are perennials, noted co-author Lee Kalcsits, a WSU tree physiologist who leads programming at the Wenatchee Fruit Tree Research and Extension Center.

“What happens in different seasons can affect the long-term health, as well as the yield and productivity of the apple tree during that specific season,” Kalcsits explained. “So what happens in winter affects what happens in spring, which in turn affects summer, and so the cycle goes on.”

With climate risks expected to increase, researchers are taking steps to help the industry adapt. Kalcsits is heading a $6.75 million USDA grant-funded project aimed at mitigating the impact of extreme weather events on apple and pear crops. The multi-agency initiative involves work across the country, particularly in apple-growing regions of Washington state.

The study was published in the journal Environmental Research Letters.

Photography: Bob Hubner, WSU Photo Services