Some of America’s top apple-growing regions are encountering significant difficulties due to climate change, as highlighted in a recent study. The research team examined over 40 years of climatic factors affecting apple trees throughout their growth cycle, from buds and flowering to fruit development, ripening, and color changes. While many cultivation areas are experiencing heightened climate risks, the three largest apple-producing counties in the U.S.—Yakima in Washington, Kent in Michigan, and Wayne in New York—are particularly affected. Yakima County, the largest of the trio with over 48,800 acres dedicated to apple orchards, showed harmful trends in five out of six analyzed metrics.
Some of the most productive apple regions in America are facing big challenges from a changing climate, according to a Washington State University study.
Researchers analyzed over 40 years of climate conditions that impact the growth cycle of apple trees from bud break and flowering through fruit development, maturation, and color development.
While many growing areas are facing increased climate risks, the top three largest apple-producing counties in the U.S. were among the most impacted: Yakima in Washington, Kent in Michigan, and Wayne in New York. In particular, Yakima County, the largest of the three with more than 48,800 acres of apple orchards, has seen harmful trends in five of the six metrics the researchers analyzed.
“We shouldn’t take the delicious apples we love to consume for granted,” said Deepti Singh, a WSU climate scientist and the study’s corresponding author. “Changing climate conditions over multiple parts of the growth cycle pose potentially compounding threats to the production and quality of apples. Moving forward, it would be helpful to think about adaptations at different stages of apple growth that can minimize overall harmful impacts.”
The team’s immediate next step is to look at projections, Singh added, to inform planning and management in the tree fruit industry.
For this study, published in the journal Environmental Research Letters, the researchers analyzed climate data from 1979-2022. They specifically looked at six metrics that impact apple growth, including two metrics of extremes—extreme heat days, defined as days with a maximum temperature greater than 34 degrees C (93 F) that can cause sunburn as well as other problems, and warm nights where the minimum temperature exceeds 15 C (59 F), adversely affecting coloration.
The researchers also considered the number of cold days; “chill portions,” which reflect the colder hours an apple tree requires to remain dormant; the last day of spring frost; and growing degree days, representing the number of days above a certain temperature favorable for apple growth.
Variations in these metrics can influence apple production, altering the timing of apple flowering, increasing the likelihood of sunburn on the fruit, and affecting both appearance and quality. The western U.S. has shown the most significant negative trends across many of these metrics.
The situation is complex, partly due to the perennial nature of apple trees, according to co-author Lee Kalcsits, a WSU tree physiologist who directs programming at the Wenatchee Tree Fruit Research and Extension Center.
“What occurs in different seasons can impact long-term health, productivity, and performance of the apple tree in any specific season,” he noted. “For instance, winter influences spring, which in turn affects summer, creating an ongoing cycle.”
Growers are already making adaptations, he pointed out, citing that in Washington state, they are implementing strategies like netting and evaporative cooling to protect apples from sunburn during increasingly frequent extreme heat events.
Given the rising climate threats, researchers are also proactively assisting the industry in adapting. Kalcsits is leading a project funded by a $6.75 million grant from the U.S. Department of Agriculture aimed at alleviating the impact of severe climate events on apple and pear crops. This is a collaborative grant involving multiple institutions, with initiatives planned across the country and within Washington state’s apple-growing regions.
“Washington is an excellent starting point for discussing adaptation,” remarked Kirti Rajagopalan, a WSU biological systems engineer and co-author of the study, who is also involved in the grant project. “Much of the commercial apple production is located in the northern U.S., and certain areas in Washington can experience high summer temperatures, making it a suitable case study. If we can manage challenges here, it likely indicates we can do so in other regions as well.”
Additional contributors to the current study include first author Shawn Preston and Matthew Yourek from WSU. This research was supported by the National Science Foundation and WSU’s Emerging Research Initiative.
