ELLENSBURG — Scanners similar to those found at airport security checkpoints, specially trained dogs and testing for cherry tree leaves are all early detection methods that cherry orchards may soon have at their disposal in the fight against “little cherry disease,” experts say.

A cherry tree infected with little cherry disease never recovers, and it can spread the problem to other trees. It’s a growing problem in Washington state, costing the tree fruit industry millions annually.

Early detection of the Little Cherry virus and X-disease bacteria is vital for growers. Several potential tools to help with that goal were discussed Wednesday during a seminar last week hosted by Washington State University’s Little Cherry Disease Extension and Outreach program in Ellensburg.

Corina Serban, leader of WSU’s Yakima-based LCD program, and her fellow WSU researchers, Tianna DuPont and Scott Harper, reviewed the two versions of little cherry disease and why they are a menace to the state’s cherry industry.

Two pathogens cause smaller, discolored, misshapen and bitter-tasting cherries: Little Cherry Virus-2 and X-disease, a bacteria spread by grafting and small leaf-hopping insects.

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% of the samples sent to WSU testing positive for X-disease by 2020.

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“Currently incidence is found throughout the growing region,” DuPont said. “The lost revenue to the industry was more than $300 million in 2020 alone.”

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.

X-disease takes time to develop, with the first symptoms usually showing up a couple of years after infection. By year five, severe symptoms can be seen in the cherries and the tree itself, Harper said.

“Infected trees never, ever, ever get better,” he added. “All trees must be scouted, and those that have reached the point of no return must be removed.”

While orchard workers inspecting the lower limbs of cherry trees (where symptoms of infection usually appear first) is one way to detect little cherry disease, three newly funded research projects hope to find earlier evidence beyond what the eyes can see.

WSU researcher Lav Khot talked about using portable Field Asymmetric Ion Mobility Spectrometry (FAIMS) equipment in cherry orchards — devices similar to the scanning equipment used in security checkpoints at airports.

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These detectors, tested in 2021 at orchards in Wapato and Buena, Yakima County, found pre-symptomatic detection of little cherry disease biomarkers during the shuck fall growth stage, after the flowering of cherry blossoms in the spring.

Khot said his team plans to collect data on Bing and Skeena varieties in 2022-23 during all six stages of cherry growth, from flowering to post-harvest.

There might be another device that can detect the early stages of little cherry disease: the well-trained nose of a dog.

Lynda Pheasant, a longtime dog trainer with the Wenatchee Kennel Club, and WSU’s Serban are working together on an agriculture dog detection program. The project launched in March 2021, with 10 dogs representing a variety of breeds who are training indoors to recognize the scent of infected branches, twigs, barks and tree roots.

This year, dogs will begin training in orchards — first in apple orchards, to get them used to the setup of fruit farms. Eventually, any in-field detection that occurs in a cherry orchard will require same-day detection by a second dog, and a sample sent to the WSU lab for confirmation.

Pheasant said canines have been trained to use their noses to find drugs, people and other animals for quite some time — and in recent years, they have been trained to detect citrus greening disease among the citrus groves of Florida and California.

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“Canine detection combined with effective tree removal could help the industry combat LCD and remain economically strong into the future,” Pheasant said.

Finally, Kelsey Galimba, a researcher at Oregon State University, laid out her team’s study of physiology-based signs of X-disease infected cherry trees.

The phytoplasma of the X-disease pathogen causes the obstruction of phloem, which inhibits the transfer of carbohydrates created by photosynthesis to other areas of a plant, such as new shoots, roots and developing fruit, Galimba said.

Sugar accumulates on the leaves of an infected plant and is converted to starch, providing a reliable marker of phytoplasma infection in other crops, such as citrus groves.

An iodine-based scratch test or spectral analysis of leaves could indicate the presence of little cherry disease before it is exhibited in the fruit, Galimba said.