Blueberry mosaic virus was confirmed in a blueberry orchard in central Kentucky this summer. This is the first report of blueberry mosaic in the state. The virus has not previously been found in southern states, but it has been reported in Michigan, Indiana, New Jersey, New York, Oregon, Washington, and British Columbia.
Formerly considered a “disorder,” blueberry mosaic has only recently been classified as a virus. Not much else is known about it. Highbush cultivars ‘Bluecrop,’ ‘Pioneer,’ ‘Concord,’ ‘Earlibule,’ and ‘Jersey’ are among the susceptible cultivars. Virus symptoms have not been reported in rabbiteye blueberry. Limited research has been conducted thus far, but it is under evaluation by a team of researchers at the USDA-ARS Marucci Center in New Jersey.
Foliar symptoms include mottling and mosaic-patterned characteristics on leaves. Patterns range from mild to brilliant with yellow, orange, and/or red colorations (see photos). Mosaic symptoms are not always produced each year, and environmental conditions may affect symptom development. It is possible that during cool seasons, symptoms are more pronounced. Thus, under ideal conditions, symptoms may appear suddenly, and it may appear that spread is rapid.
Infected plants often result in reduced fruit load. Yield losses of 15% have been reported on ‘Bluecrop’ in Michigan. Fruit on infected plants have been shown to ripen later than noninfected fruit, and fruit quality is low.
The vector (carrier) of the virus is not known. Researchers report that blueberry mosaic is not transmissible by mechanical means (i.e. pruners). However, the virus is graft transmitted. Because virus particles are systemic (dispersed throughout the vascular system), once infected, all plant parts are infected, even when symptoms are absent. Thus, cuttings should never be taken from a virus-infected plant.
As mentioned above, the vector of blueberry mosaic virus is not known. Therefore, growers are encouraged to destroy infected plants until it is clear on how the virus spreads. Whether an insect vector is involved is yet to be determined.
Current research indicates that the virus is slow-spreading (if at all) under field conditions. However, in Michigan, spread is rapid. So far, the reason is unknown.
There is no cure for plant viruses, including blueberry mosaic. Growers should remove infected plants and destroy them by burning or burying. Remove all roots within soil, as well. Scout orchards, especially nearby plants, several times during the growing season. Contact a local extension agent if a plant appears suspicious.
Most importantly, purchase plants from a reputable grower. Visit nurseries before plant purchase and ask to inspect parent plants. Furthermore, a virus-free certification is always worth the extra cost.