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Canines could sniff out trouble in Central Washington orchards

Dog testing shows positive results in finding disease

By Joel Donofrio, Yakima Herald-Republic
Published: January 31, 2025, 5:56am

YAKIMA — Dogs and their extremely sensitive noses have been used to sniff out hidden drugs, track down fleeing criminals and even help authorities search for tracking devices in domestic violence situations.

In the next few years, specially trained canines could be used to detect a costly problem for Central Washington cherry growers: the presence of little cherry disease viruses and the similar X-disease pathogen in trees.

“Dog testing is showing positive results, given that they can examine the whole tree,” Corina Serban, leader of Washington State University’s Yakima-based little cherry disease program, told attendees at a Cherry Institute meeting Jan. 10.

Early detection of little cherry disease or X-disease by other methods, such as a molecular qPCR lab analysis, allows only a small portion of a tree to be tested, Serban said.

With the early stages of the disease usually occurring in only a small portion of the tree, and outward signs of the disease not visible until the tree has been infected for at least three years, dogs who can accurately detect infected trees could be a huge help to cherry growers, she added.

“Tissue taken for a PCR (test) is about the size of a Tylenol pill,” Serban said in a follow-up interview with the Yakima Herald-Republic. “If you don’t take tissue from the right place, you might miss (the infected area).

“PCR only tests a small part of the tree and is very destructive,” she added. “Dogs test the whole tree, and at this point they have been extremely accurate. They haven’t alerted on a (noninfected) tree.”

An increasing problem

Little cherry disease is a general term for pathogens that infect trees and cause smaller, discolored, misshapen and bitter-tasting cherries.

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A cherry tree infected with one of two little cherry disease viruses or the similar X-disease pathogen never recovers, and can spread the problem to other trees before infection is noticed.

WSU researchers Tianna DuPont and Scott Harper have reported how X-disease, a bacteria spread by grafting and small leaf-hopping insects, is spreading much more rapidly than the viruses in Washington.

DuPont noted that the cherry-growing regions of Central Washington went from several hundred trees testing positive for X-disease in 2016 to thousands of infected trees five years later, with about 36 percent of the samples sent to WSU testing positive for X-disease by 2020.

She estimated the diseases cost the Northwest’s cherry industry at least $300 million annually, the WSU Tree Fruit research website reports.

Harper said little cherry disease doesn’t just affect the appearance of the fruit. Pulp color and maturation are also reduced, lessening the amount of sugar in the cherry and resulting in its poor taste.

“Really, the key message is, if you have infected trees, remove them,” Serban told the cherry growers at this month’s meeting in Yakima. “Once a tree is infected, there is no cure, making early detection critical to prevent the pathogen’s spread and economic losses.”

Dog training and testing

Early detection is where dogs and their sensitive noses could prove helpful to the cherry industry and orchard owners.

After a study was launched in 2021 with the Wenatchee Kennel Club, a new collaboration between WSU researchers and Buhl, Idaho-based Ruff Country K9 owner Jessica Kohntopp began in 2023.

Kohntopp has two dogs, a Belgian Malinois named Aika and a Dutch shepherd named Humma, who were trained to detect little cherry disease pathogens. In a blind greenhouse study with potted cherry trees, the dogs successfully identified seven known infected trees and one additional tree later confirmed positive through qPCR testing, Serban reported.

Aika and Humma were brought to a USDA cherry tree research orchard in Moxee during the summer, then to a commercial orchard with young cherry trees in November. In both tests, the dogs alerted on nearly all the known infected trees and never alerted on a negative tree, Serban said.

“Jessica runs the dogs through on a leash. She goes into tree rows where we know at least one tree is positive,” Serban said of the tests. “The dogs sniff each tree, and are trained to sit, to put their butt down, if it’s positive.

“Jessica will try to pull the dog to the next tree, but if a dog is really sure about that tree, you cannot move them,” she added. “They stay by that tree and wait for their reward” — a toy they briefly get to play with.

The controlled study in the USDA orchard showed a sensitivity rate of 96 percent, with the dogs combining to find 48 out of 50 infected trees. The November study, done on dormant trees rather than fruit-bearing ones, found the dogs locating all four known positive trees, Serban said. They flagged 51 additional trees, which will be tested this year.

“Scott Harper and I will dig up five trees the dogs flagged — roots and all — and we’ll test them and see if we can find at least one positive (portion of the tree),” Serban said. “I tested four of the (additional flagged trees) and they all came back a very weak positive, with early stages of disease.”

Next steps

The ability of dogs to detect little cherry disease at its earliest stages, and at low amounts in newly infected trees, is a positive and important sign, Serban said.

“We need to see if they can find it at the nursery level — before the owners buy the trees,” she said. “We really want to do a nursery study, to see if it works in that setting.”

The two-year canine detection project finishes in May, and Serban is seeking funding for another year or two of study. If positive results continue, Kohntopp is working on a business plan so dogs could be used by orchard and nursery owners.

“As a researcher, you really want to make sure you don’t send these dogs into an orchard and they falsely alert,” Serban added. “Jessica would like more data but she is really confident that the dogs are finding it.

“Growers are interested and they would definitely hire her,” Serban said. “But she wants to be conservative. She comes from a background of training dogs to detect (citrus grove diseases) in Florida, so she is very knowledgeable. Working with her has been wonderful.”

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