Cause The blueberry shock virus (BlShV), which is pollenborne. Transmission occurs when pollinators, especially foraging honeybees, transfer infected pollen to flowers on healthy plants. The cultivars Berkeley, Bluegold, Bluetta, Cargo, Duke, Liberty, Aurora, Pemberton, Reka, and Elliott are particularly susceptible and the virus spreads rapidly through a field. In 'Bluecrop', 'Bluejay', 'Mini Blue', 'Calypso', 'Legacy', 'Perpetua', 'Reka', and 'Toro' the virus spreads very slowly in the field. The disease cannot be eliminated by removing and destroying plants with symptoms once it appears in a field. Plants that have recovered from the symptoms appear to produce a full crop, but these plants can continue to serve as an inoculum source for nearby plants and for any new plantings. Plants (such as Huron) that are infected within the first year or two after planting may be more seriously affected by this disease than older plants. The disease has been confirmed in Oregon (from Eugene northward), Washington and British Columbia. It has not been found in southern Oregon. Many states and countries require testing and certification of nursery stock as free of shock and scorch.
Cranberry was initially thought to be a symptomless host but it has been associated with cranberry fruit scaring.
Symptoms Flowers and young vegetative leaf shoots suddenly die in spring when flowers are just about to open. The entire bush may be blighted, but more commonly only a portion of the branches will show symptoms. These symptoms represent the plant's "shock reaction" to infection. Blighted tissues drop; as the season progresses, a second flush of leaves is produced. By late summer, affected plants look normal except they produce little fruit. Leaves that do not blight in spring may show thin red ringspots on both sides of the leaf. Plants may exhibit the shock reaction for 1 to 3 years and may be symptom-free thereafter although they still carry the virus.
Once plants recover, they may continue to show leaf discoloration including spots, line patterns, blotches and/or reddening for several more years. These "after shock" symptoms were intense on leaves formed during the cool wet spring of 2010 but lessened on leaves produced after warm dry conditions prevailed in the summer.
Cultural control
- Use certified planting stock for new plantings.
- Do not establish new fields adjacent to infected fields.
- Maintain good cultural care of infected plants while they are going through seasons with the shock reaction.
- For small plantings, let the disease run its course. In larger plantings, rogue plants only if infected ones are confined to a small area; otherwise let the disease run its course.
References Bristow, P.R. and Martin, R.R. 1999. Transmission and role of honeybees in field spread of Blueberry shock ilarvirus, a pollen-borne virus of highbush blueberry. Phytopathology 89:124-130.
Pscheidt, J.W., and Harper, N. 2014. Progression of symptoms on blueberry infected with blueberry shock virus. Plant Health Progress doi:10.1094/PHP-RS-13-0121.