Apple orchards face compounding threats from climate change

A recent study from Washington State University (WSU) reveals that climate change poses significant challenges to apple orchards in some of the most productive regions of the United States.

The researchers conducted an extensive study that included over four decades of climate data. They analyzed how varying weather conditions influence the critical growth stages of apple trees.

These stages include bud break, flowering, fruit development, maturation, and color development – all of which are crucial for healthy yields and high-quality apples.

Climate change and apple growth

The study revealed alarming trends, particularly for the three most productive apple-growing counties in the United States: Yakima County in Washington, Kent County in Michigan, and Wayne County in New York.

Among these, Yakima County – a powerhouse with over 48,800 acres of apple orchards – was found to be the most severely affected.

Yakima County exhibited harmful trends in five out of the six climate metrics studied, indicating the region’s heightened vulnerability. These metrics include factors like extreme heat, warm nights, reduced cold periods, and shifting frost dates, all of which disrupt the delicate balance needed for apple growth.

The findings highlight the region’s significant exposure to the negative impacts of climate change, which could challenge its status as a leading apple producer in the future.

Climate metrics and apple production

Apple production relies on specific climate conditions to ensure healthy growth, high yields, and good fruit quality. However, shifts in these conditions pose significant challenges:

Extreme heat days

When temperatures exceed 93°F, apple trees face stress that can lead to sunburn on the fruit, reducing apple quality and marketability. Prolonged exposure to such heat can also impair tree health and productivity.

Warm nights

Nighttime temperatures above 59°F interfere with apple coloration. Proper color development is essential for market appeal, as it affects both the visual and perceived quality of the fruit.

Cold days and chill portions

Apple trees need a specific number of cold hours (known as chill portions) during dormancy to reset their growth cycle. A reduction in these cold periods can lead to irregular flowering and lower yields.

Spring frost timing

Changes in the timing of the last spring frost disrupt the blooming process. Late frosts can damage blossoms, leading to fewer fruit or misshapen apples.

Growing degree days

Warmer overall temperatures accelerate the growth process, potentially causing premature fruit development. This can affect the size, flavor, and storability of apples.

These changing climate conditions upset the delicate balance required for consistent and high-quality apple production. The western U.S., a major apple-producing region, has experienced the most pronounced negative trends in these metrics.

This raises concerns not just for regional growers but for the entire U.S. apple industry, as these changes threaten both the quantity and quality of the fruit.

Compounding threats of climate change

“We shouldn’t take the delicious apples we love to consume for granted,” said Deepti Singh, 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.”

This complexity stems from the perennial nature of apple trees. “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,” explained Lee Kalcsits, a WSU tree physiologist.

Protecting apples from climate change

Apple growers in Washington state are implementing adaptive measures to combat the effects of extreme heat on their crops.

Techniques like netting, which reduces direct sunlight to prevent sunburn, and evaporative cooling, which uses water misting systems to lower orchard temperatures, are helping protect fruit quality and tree health.

These adaptations highlight both the resilience of the apple industry and the urgency of addressing climate change challenges. To support growers further, WSU researchers are working on large-scale solutions.

Led by Lee Kalcsits, a $6.75 million USDA-funded project aims to mitigate the impact of extreme climate events on apple and pear crops.

This collaborative, multi-institution effort seeks to develop strategies that growers across the nation can use to sustain production in an increasingly volatile climate.

A blueprint for the future

“Washington is a great place to start to talk about adaptation,” said Kirti Rajagopalan, a WSU biological systems engineer and study co-author.

If successful, the strategies tested here could serve as a blueprint for apple-growing regions nationwide.

As climate change risks grow, the apple industry’s ability to adapt will be crucial. With ongoing research and innovative solutions, there’s hope that the apples we cherish can continue to thrive in a changing world.

The study is published in the journal Environmental Research Letters.

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