By Tony Buhr

The Wenatchee World

In the midst of COVID-19, cherry growers around the Wenatchee Valley are battling another epidemic: little cherry disease.

The number of positive cases of the disease have tripled in the last two years, according to the WSU Tree Fruit website. The disease causes cherries to grow smaller, paler and lose their flavor. One of the pathogens can also impact nectarines, peaches, plums and apricots.

“They both cause similar symptoms so we call it little cherry, but it is really two pathogens,” said Tianna DuPont, WSU Tree Fruit Extension specialist.

In 2019, WSU Tree Fruit Extension staff tested 7,000 samples from cherry trees and 2,629 positive samples came back, DuPont said. In 2018, fewer than 600 trees were found to be positive with the pathogens. Growers around the state removed 28,000 trees this winter to stop the spread of the disease.

Of the 2,629 positive cases, 141 of the positives were located around the Wenatchee Valley, according to a WSU Tree Fruit website.

It is almost impossible to know the trees have the disease until right before harvest, DuPont said.

Harvest is underway in the southern part of the cherry-growing area, said James Michael, marketing vice president for Northwest Cherry Growers. The Chelan County harvest will begin next month. Northwest Cherry Growers predicts growers across five states will produce about 21 million boxes of cherries this year compared to about 23 million boxes harvested in 2019.

WSU extension employees are asking growers to be aware of the ongoing problem and spend time scouting and removing trees during the 2020 harvest. It is suspected that the problem will get worse before it gets better.

There is no cure once trees are infected and the only way to stop the spread is to remove the infected trees, DuPont said. But certain types of insects, such as mealybugs and leafhoppers may transmit the disease.

“So primarily by insects, but it can also be spread by grafting and root grafting,” she said. “So, it is important for growers to start with clean plant material.”

Growers have some options when it comes to controlling pests that could be spreading these diseases, according to the WSU Tree Fruit website. Certain insect species like lacewings, minute pirate bugs, spiders and lady beetles are effectives at controlling mealybugs. So it can be important not to spread pesticides that hurt these types of insects.

Other possibilities could include using white reflective mulch in orchards to confuse insects so they can’t find trees, DuPont said. It reduces their ability to feed on the trees and move around.

“So we’re trying to find alternatives to pesticides as well, in order to make it so we have integrated pest management and don’t create other problems,” she said.