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USA - Cherry disease continues to decimate crops in Yakima Valley

Foreman Hector Torres oversaw the removal of a diseased cherry tree at Barrett Orchards on Thursday.

The tree started producing small, discolored cherries, symptoms of a cherry disease that orchard owner Mark Barrett first encountered in his crops about four years ago.

That first year, when Barrett’s trees started to die, he instructed staff to cut off the impacted limbs. But he soon learned that wasn’t enough. The disease — X-disease phytoplasm — infected the entire tree, including its root system, and started spreading throughout the orchard.

The next year, he had to remove 3 acres of orchard. Last year, he had to remove another 7 acres for a cumulative total of one-third of his acreage. It’s land he’ll have to leave unplanted for at least a year or two, and then fumigate, to ensure the disease won’t impact future crops.

The economic loss has been significant, he said.

“We’re losing 75 tons of fruit out of one block, with no future for that block,” he said. “We had invested everything. Economically, it’s huge.”

Barrett Orchards is not alone in battling cherry disease. More than 20,000 cherry trees were cut down last year alone in Yakima County, according to Tianna DuPont, a specialist with the Washington State University Tree Fruit Research and Extension Center. But DuPont added those numbers were based on a survey where only about 20 growers responded.

“We know those numbers are likely a pretty severe underestimate,” she said.

While cherry disease can be spread by a number of pathogens, the two most prevalent in Yakima Valley crops are caused by X-disease phytoplasma and Little Cherry Virus 2. The diseases are transmitted by leafhoppers and mealy bugs, respectively. When the insects feed on infected phloem in plants, the pathogens make a circuit from saliva to the insects’ blood — an incubation period that takes a few weeks — and then back through the saliva to re-infect new plants on which the insects feed.

Healthy trees also can become infected by root systems from infected neighbors or grafts from infected trees. The disease stays alive in soil, living in diseased roots that were left behind.

The only solution is to completely remove any infected trees, poison the root systems, and take out any surrounding trees that might have become infected, DuPont and local growers said.

‘This is people’s livelihoods’

DuPont said the cherry diseases have reached epidemic proportions in Washington over the past few years. Last year, close to 3,000 samples tested — or about 38% of those submitted — tested positive for the disease, which was up from 25% the year before.

Garrett Bishop, with the crop consulting company G.S. Long, said he’s fielded more calls this year about cherry disease than any other in his five years working with cherry viruses with the company. Bishop said the disease tends to at least double its damage each year. Growers who lose 5% of their crops the first year likely will lose 10% the next year, then 20%, then 40% he said.

“It’s getting worse and worse,” he said. “This is serious. This is people’s livelihoods. To watch entire blocks get removed is devastating.”

Farmer Mike Van Horn, who grows apples, pears, and cherries on a 160-acre orchard in Zillah, has been battling Little Cherry Virus 2 for years. He first noticed symptoms in an older orchard about three years ago. Since then, he’s had to remove about a quarter of the cherry trees in one of his 6-acre blocks.

“I was surprised by how quickly it spread,” he said.

Bishop said that while Little Cherry Virus disease impacts only cherries, X-disease can spread to other crops, such as peaches, nectarines and plums.

“If there is only one host, there’s a better fighting chance for growers,” he said. “But there are certain types of growers who are cherry growers, and they are going to try to fight this as best they can. There’s no doubt about that.”

DuPont said the only way growers can know for sure if their orchards are infected is to send cuttings to a lab. Washington State University’s lab has been turning around results within one to six weeks, a longer period than the hoped-for seven to 10 business days.

The delay has been due in part to reduced lab staffing but also because the labs use equipment and chemicals similar to those used to test people for COVID-19, DuPont said.

Barrett still has a 10-acre block of young, healthy cherries that he plans to continue cultivating. But he said it’s unlikely that he’ll plant additional cherries, given the prevalence and the damage of cherry disease.

“We would need the science to protect the trees before we could do that,” he said. “Right now, I’m not comfortable planting any more cherries.”

Van Horn also isn’t planning on replanted cherries within the infected block.

“The risk of replanting cherries is higher than I want to take on right now,” he said.

What to do?

When Van Horn’s staff encounter diseased crops, they cut down the infected trees and paint the trunks with herbicide to kill the roots. They also remove any neighboring trees that show negative effects after the herbicide application, since that’s an early sign the tree was connected to the diseased one and also likely carrying the disease.

Bishop said that’s an important step, as a tree is usually infected for years before it shows symptoms, a period of time when the tree can transmit the disease to others.

“What you have to keep in mind is that when a tree starts showing symptoms, it’s probably been infected for between one and three years,” Bishop said.

This harvest, Barrett’s staff also will mark infected trees during harvest. They’ll drill holes into the infected trees that they’ll fill with the herbicide Roundup, which the infected trees’ root systems will carry to any intertwined roots in the neighboring trees that also might have been infected.

Then they’ll pile up the infected trees and burn them.

“The reason I’m more aggressive now in eradicating it is I don’t want it to spread to the other blocks,” Barrett said.

Although both Barrett and Van Horn prefer to use integrated pest management, a technique that reduces the amount of insecticides that need to be sprayed, both plan to rigorously spray their cherry crops through October, using guidance from WSU research studies.

Barrett hopes future research will focus on how growers can tell when it will be safe to replant the infected orchard land. Van Horn is interested in possible natural predation methods, in which he could use predators of leafhoppers and mealy bugs to reduce the amount of chemicals his staff have to spray.

Dupont, the WSU tree fruit specialist, said researchers are focusing on the leafhopper, about which not much is known. Researcher Tobin Northfield is running large-scale trials in Yakima and Wenatchee using Kaolin clay and Extenday, tracking leafhopper numbers and species across each commercial block. Researchers also are looking at food sources and alternative hosts for leafhoppers.

Van Horn, who never intended to be a farmer when he was growing up but has been in the business now for more than 40 years, said he’ll stick with it.

“It’s hard. We deal with unpredictable weather and labor, but we have to accept what is and work to change the things we can change,” he said. “It’s a great place to work and live, and I hope we can continue doing it.”

Source – http://www.chronline.com