Climate change poses major challenges for some of the most productive apple growing regions in the U.S. — particularly Washington’s Yakima County.

A new study from Washington State University analyzed more than 40 years of climate conditions that impact the growth cycle of apple trees.

Yakima County, with more than 48,800 acres of apple orchards, saw harmful trends in five of the six metrics analyzed.

That included days with maximum temperatures more than 93 degrees, which can cause sunburn damage. Those increased from about five days on average in the early 1980s to more than 10 days in recent years, researchers said, in a joint email.

Extremely warm fall nights with temperatures above 59 degrees, which can negatively impact color development and fruit maturation, also nearly doubled in the past four decades.

For the Yakima area, the last day of frost now occurs about a month earlier than in 1980.

“The direction of these trends is pretty consistent across the Northwest, though some of these changes are more amplified east of the Cascades,” the researchers wrote.

Threats to production, quality

Deepti Singh, a climate scientist and one of the study’s authors, said in a news release that people shouldn’t take apples for granted, as changing conditions pose potentially compounding threats to production and fruit quality.

Researchers’ next step is to look at projections to inform planning and management in the tree fruit industry, she added.

The probability of temperature-related fruit losses from extreme weather is increasing. “However, we don’t know the economic impacts of these losses just yet. We are just starting a new federally funded project that will quantify the economic impact from extreme temperature events,” researchers wrote, in the email.

Scientists also said potential increases in pests, diseases and water scarcity could further increase the direct climate risks to apple production.

The joint email was crafted by Singh, Lee Kalcsits, a tree physiologist who leads programming at the Wenatchee Tree Fruit Research and Extension Center, and Kirti Rajagopalan, a biological systems engineer.

Complex problems, adaptation

Because apple trees are perennials, the study poses complex problems.

“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,” Kalcsits said, in the news release.

Growers are already adapting by employing measures such as netting and evaporative cooling to fend off sunburn during more frequent extreme heat.

Those practices can be expensive though. Permanent netting can cost up to $10,000 per acre, though drape netting is about half that. Evaporative cooling and fogging systems range between $2,000 to $4,000 per acre. Spray protections vary in cost, but are still the cheapest action, researchers said.

Scientists also are taking steps to help growers.

Kalcsits is leading a project funded by a $6.75 million USDA grant to mitigate the impact of extreme climate events on apple and pear crops. Work is planned across the nation and includes partners such as Oregon State University.