At a Glance

Researchers have dubbed the affliction "Rapid Apple Decline."Apples are a $4 billion industry in the United States.Some say extreme climate could be to blame.

Something is killing America’s apple trees, and researchers are scrambling to get to the root of the problem before it spreads across the country’s $4 billion industry.

Scientists and growers alike are stumped by Rapid Apple Decline (RAD), sometimes also called Sudden Apple Decline, an overarching term dubbed by the Pennsylvania Department of Agriculture to describe the condition that no one has been able to specifically identify.

The first signs of trouble are when an apple tree’s leaves start to curl up and turn yellow, brown or dark red. Within two weeks, the tree is dead.

Kari Peter, a plant pathologist at Pennsylvania State University who studies diseases in apple and other stone fruit trees, . So far, her lab has not found a common cause.

"One grower has lost ," Peter told Good Fruit Grower. "He’s losing trees every year."

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RAD has been observed mostly in the central, northeast and northwest regions of the United States, and also in Ontario, Canada.

The U.S. is the second-largest grower of apples in the world, next to China. More than 7,500 growers nationwide grow , according to the U.S. Apple Association, with an annual direct revenue of $4 billion and another additional $15 billion of related downstream economic activity.

Peter and others have theorized that everything from extreme weather to some yet-to-be-discovered bacteria could be a cause of RAD.

In a paper in the science journal Plos One, researchers studied honeycrisp apples in New York to determine a cause of RAD. The study considered several environmental factors, including weather, soil, roots, bacteria and fungi, and tested affected trees for six different viruses.

They found no single, common factor that was causing the apple trees to die.

Peter is warning apple growers to brace for a potentially difficult season this year.

“I’m worried that since last year was so stressful, I hope I’m proven wrong, but I think we are going to see another wave,” she told Good Fruit Grower.