Researchers use dogs to ‘sniff out’ infected cherry trees in Eastern Washington

Washington State University researchers are piloting new efforts to “sniff out” little cherry disease early enough to allow Eastern Washington cherry growers to remove infected trees before the disease can spread further.

The disease has reached epidemic levels in Yakima, Benton and Franklin counties and has cost growers across the state millions of dollars in tree removal and lost revenue.

“Finding the little cherry disease for a grower is pretty bad news,” said Corina Serban, who leads WSU’s Little Cherry Disease Extension and Outreach program. “The grower cannot put that fruit on the market.”

Little cherry disease symptoms only show up in fruit, making early detection difficult

Serban said when researchers talk about little cherry disease, they’re often using is an an umbrella term for two different pathogens — Little Cherry virus-2 and X-disease phytoplasma — that cause similar symptoms.

Infected trees might produce cherries that continue to look like they’re unripe just before harvest: they’re often smaller, bitter or bland-tasting, poorly colored and overall unmarketable.

Serban since the leaves don’t show any symptoms, growers can’t identify infected trees early in the season. Instead, they have to wait until just before harvest, when the diseased cherries will stick out among those that are ripe and healthy.

However, Serban said growers won’t be able to tell a tree is infected until two to three years later, when the first symptoms start to appear. She said that’s why researchers call it a “silent disease.”

“The grower needs to stay ahead of the game and save his orchard and scout aggressively and remove aggressively,” Serban said.

Serban said growers should look for trees that seem to be exhibiting symptoms of little cherry disease, mark them, take samples and send them off to a lab to get them tested for both pathogens.

“Once you have the results back from the lab and you have a confirmed positive in your orchard, the recommendation is to remove it as soon as possible,” Serban said.

Dogs trained to “sniff out” little cherry disease in Eastern Washington orchards

Researchers met with local growers Tuesday at the Messimore orchard in Buena to demonstrate several little cherry disease pilot projects, including training companion dogs with the Wenatchee Kennel Club to identify infected trees.

“Right now, the dogs are pretty good at detecting the infected samples, but we don’t know exactly what they’re smelling,” Serban said.

Serban said another team of researchers — from WSU and the U.S. Department of Agriculture’s Physiology and Pathology of Tree Fruits Research Unit in Wenatchee — is working to come up with the answer to that question.

The team is using portable field asymmetric ion mobility spectrometry (FAIMS) — similar to the technology they use to screen for explosives at airport security — to identify the volatile biomarkers that may indicate the onset of little cherry disease.

“They’re using like an electronic nose or a sniffer machine to detect the volatiles in the samples,” Serban said.

Both projects have received grant awards from the Washington Tree Fruit Research Commission.

Without early intervention, Eastern Washington orchards could face mass tree removal

For Little Cherry virus-2, apple and grape mealybugs are the vectors — or the agents that transmit the pathogen to other living organisms — and can often be managed with pesticides the growers are already using.

Researchers are more concerned with the vectors for X-disease, which are tiny pests known as leafhoppers that can move more quickly and infect more trees than the vectors for Little Cherry virus-2.

“In the case of the X-disease, what growers can do is to actively monitor the presence of the leafhoppers on their orchard floor,” Serban said. “They can do that with sticky cards for the insects.”

Another project researchers are working on looks at replanting strategies growers can use when putting new trees in blocks previously infected with X-disease, specifically whether they might be re-infected by remaining root systems.

“We’re tracking those and those recommendation will come soon,” Serban said.

Serban said researchers are studying several trees in the orchard in Buena, which has replanted new trees in the same area they removed the diseased trees from.

Several of those trees have cages around them to protect them from leafhoppers. Serban said researchers want to make sure that if the tree tests positive for X-disease, they’re sure it’s because of the root systems and not from a stray leafhopper.

More information on little cherry disease can be found here.

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