THE DALLES, Ore. – X disease has become a serious problem in the cherry growing regions of Oregon and Washington, causing growers to remove hundreds of valuable trees from their orchards.
Also known as little cherry disease, X disease was first identified in Oregon in 2017. X disease decimated the cherry industry in California twice – in the 1940s and 1990s.
This year, Oregon State University Extension came prepared to help growers spot the dreaded disease prior to and during this year’s harvest that began in June.
In March, OSU Extension created a card that field workers could use to identify X disease in orchards. One side of the card is in English and the other side is in Spanish. The card describes disease symptoms, includes a photo of affected fruit, and features a QR code that leads to the X disease entry in Pacific Northwest plant disease handbook.
Cherry virus and virus-like problems are common in orchards throughout Oregon, and range from the mostly benign to lethal. The most serious viruses, such as X disease, spread quickly throughout a growing region, significantly reducing fruit quality and yield.
Controlling these diseases is vital to the health of Oregon’s cherry industry. X disease is incurable and will spread rapidly, so the primary method to control it is cutting down symptomatic trees as soon as possible, preferably during the growing season.
Ashley Thompson, an assistant professor of horticulture and fruit tree Extension specialist in Hood River and Wasco counties, said growers had become so cautious about X disease, they were cutting down trees that might not have been affected.
“Identifying cherry viruses based on symptoms can be confusing,” Thompson said. “For example, X disease can be confused with small cherries, which are small but ripen normally. We don’t want our cherry growers to remove trees if they don’t have to.”
X disease symptoms are little, pale-red to greenish-white fruit that do not taste ripe. Some cherries might be pointed or flat-sided. These cherries will not ripen. Normal-looking fruit on a branch with unripe fruit will have poor flavor. Symptoms are most noticeable two weeks before harvest and through harvest when normal looking fruit is mature.
Since she came to OSU in the spring of 2018, Thompson has been working alongside OSU colleagues Jay Pscheidt, a professor of botany and Extension plant pathologist, and doctoral candidate Lauri Reinhold, to help cherry orchardists mitigate the spread of X disease in the Columbia Gorge.
In 2019, Thompson identified 52 trees infected in Wasco County and provided growers with bilingual flyers describing X disease symptoms. She also highlighted X disease and other serious cherry viruses at Extension’s annual cherry pre-harvest tour in The Dalles.
She is a member of the Little Cherry Virus Task Force, an initiative of Washington State University and the Washington State Tree Fruit Research Commission.