Cherry (Prunus spp.) - X-Disease
Cherry Cultivar Susceptibility
Cause Little cherry virus (LChV) consists of two different closteroviruses that result in similar symptoms. LChV-1 and LChV-2 have been described from Oregon and Washington including a mixed infection of both viruses. Statewide surveys in Oregon in the late 2010s did not find LChV-2 but it was detecting on cherry in Parkdale, OR in 2021. A strain of LChV-2, formerly known as the Kootenay little cherry disease and as LChV-3, has been severe in many sweet cherry orchards in British Columbia. Little cherry virus can be carried by ornamental flowering cherries such as Prunus serrulata, 'Kwanzan' and 'Shirofugen' and has also been referred to as K&S disease. The host range of LChV-1 is not well understood but appears to be more widespread than LChV-2, but it is also less serious and much harder to identify visually. The apple mealybug (Phenacoccus aceris) and the grape mealybug (Pseudococcus maritimus) are vectors of LChV-2. Grafting infected scion or rootstock can also transmit the disease as well as natural root grafts. There is a one-year lag between infection and symptom development. There are two distinct phases of infection by LChV-2. The early phase is characterized by scattered distribution and low titer corresponding to mild or no symptoms. The establishment phase that corresponds to systemic virus distribution and expression of severe symptoms. Little cherry disease is distinct from X-disease, which has similar symptoms but is caused by a phytoplasma.
'Deacon', 'Lambert', and 'Sam' are most susceptible to little cherry disease but it also occurs in 'Bing' and 'Sweetheart.'
Symptoms Main symptoms of black cultivars are small, poorly colored fruits with poor flavor. Check the flavor of fruit on limbs or trees with pink fruit when the rest of the trees are turning red or mahogany. Some cultivars such as Lambert also develop a slightly pointed or triangular appearance. In light-color cultivars, such as Royal Ann, the fruit is small and pinkish. Trees may lose some vigor, but in general there is no visible impact on overall tree health. Some cultivars develop a premature red leaf discoloration in the fall. Cool springs may intensify symptoms. 'Bing' may exhibit small fruit for two seasons and then return to normal; however, the flavor never recovers. Fruit on 'Rainier' may look white. Trees with symptoms tend to be in pockets or groups in the orchard.
Trees infected with X-Disease will also have symptoms of little, off-colored cherries.
Sampling Sample fruit stems and/or woody tissue at harvest for either viruses or phytoplasmas. Although Little cherry virus 2 can be detected in all tissues of the tree all year around, X-disease, which causes similar symptoms, is best sampled at harvest. Early detection will aid in management of these diseases.
- Establish new orchards only with nursery stock tested and found to be free of all known viruses. Virus-tested 'Kwanzan' and 'Shirofugen' trees have been released to nurseries for propagation.
- Check the flavor of fruit on limbs or trees with pink fruit when the rest of the trees are turning red or mahogany. If poor flavor then flag the limb for tree removal.
- Control programs for the apple and grape mealy bug will reduce spread in affected orchards. Apply insecticides prior to tree removal. See PNW Insect Management Handbook for details.
- Remove infected trees and immediately apply glyphosate (such as Agri Star GlyStar Original) to the cut stump following the procedure outlined on the label. Cutting, scoring or drilling holes into the stump will aid in herbicide uptake. In addition to killing roots and suckers, this will allow you to identify root grafted trees, which are also infected with the virus and need to be removed.
- Remove infected flowering cherries or wild seedlings growing near sweet or sour cherry orchards.
Note It is illegal to ship flowering cherries into the little cherry control areas of British Columbia. It is also illegal to grow flowering cherries in the control areas without permission.
Reference Galinato, S., Gallardo Llanos, R.K., Beers, E., and Bixby Brosi, A. 2019. Developing a Management Strategy for Little Cherry Disease: The Case of Washington State. Plant Disease 103:2184-2190.