Climate change is hampering US apple quality and output: Study

Many of the nation's biggest apple-generating regions are confronting challenges in crop growth and development, due to the impacts of a changing climate, a new study has found.

While apple orchards nationwide have become increasingly vulnerable to warming trends, the three U.S. counties with the biggest output are among the most affected, according to the study, published on Monday in Environmental Research Letters.

At the top of that list was Yakima County, Wash., which is home to more than 48,800 acres of orchards — and which showed worrisome signs in five of six metrics analyzed by Washington State University scientists. Next in line were Kent County, Mich., and Wayne County, N.Y.

“We shouldn’t take the delicious apples we love to consume for granted,” said corresponding Deepti Singh, a Washington State climate scientist, in a statement. “Changing climate conditions over multiple parts of the growth cycle pose potentially compounding threats to the production and quality of apples.”

Worldwide, the U.S. is ranked third among apple exporters, trailing behind the European Union and China during the 2022-23 season, according to the US Department of Agriculture.

At a state level, Washington is the biggest annual producer, followed by Michigan, New York and Pennsylvania. The top markets for U.S. apples are Mexico, Canada, Taiwan and Vietnam.

Using historical trends and climate metrics, the Washington State scientists evaluated six metrics that could affect apples over more than four decades, from 1979 to 2022.

The metrics included the number of extreme heat days, warm nights and cold days, as well as the quantity of chilly hours needed for a tree to go dormant, the last day of spring frost and the quantity of "growing degree days," or those above a certain temperature that are conducive to apple growth. 

Shifts in these metrics, the authors explained, can alter the time when apple flowers bloom, while also raising the risk of sunburn on apples and influencing appearance and quality.

The U.S. West has undergone the strongest such detrimental changes across multiple metrics, according to the study. 

Making these developments more complex is the fact that apple trees are perennials — meaning, they bear fruit for many years.

“What goes on in different seasons can affect long-term health as well as the performance and productivity of the apple tree during that specific season,” co-author Lee Kalcsits, a Washington State tree physiologist, said in a statement. “It just keeps going around in a cycle."

With these cyclical knock-on effects in mind, Washington state producers are now using netting and evaporative cooling to stave off sunburn, according to Kalcsits. 

The researchers also stressed that not all the observed climatic shifts are having negative impacts on apple cultivation, as some regions are actually benefiting from the changes.

"Fewer cold degree days and earlier last day of frost could be beneficial by reducing exposure of apples to freezing temperatures allowing the use of less cold hardy crop varieties," the scientists stated.

"Yet, it could also diminish plant cold hardiness, increasing vulnerability to extreme cold events," they added.

Co-author Kirti Rajagopalan, a Washington State biological systems engineer, described Washington as an ideal case study, especially since parts of the state endure hot summers.

"If we can manage it here, then it's likely manageable elsewhere too," Rajagopalan continued. 

Going forward, the authors emphasized the importance of tailoring adaptive measures to varied stages of apple growth — an effort that Singh said could "minimize overall harmful impacts.”