Cause A virus complex consisting of Raspberry bushy dwarf virus (RBDV) and Raspberry leaf mottle virus (RLMV), Raspberry latent virus (RpLV), and/or Black raspberry necrosis virus (BRNV). The cultivar Meeker had more severe growth reductions when infected by RBDV and RLMV; whereas crumbly fruit was more prominent when infected by RBDV and RpLV or three viruses together (RBDV, RLMV, and RpLV). RBDV is spread by pollen while the others are aphid-vectored. RLMV spread rate is much higher than that of RpLV, which needs a 6 to 7 day period in the aphid to become transmissible.The disease can be found on many red and black raspberry cultivars as well as 'Boysenberry', 'Loganberry', and 'Marionberry' blackberries. Entire fields may become infected with the virus within 3 to 5 years of planting, depending on inoculum pressure from adjacent fields. The fruit from infected plants often will not make IQF grade and is sold as a lower value produce for juice, jam or puree. Since pollen is infected with RBDV honeybees play an important role in moving infected pollen from plant to plant.
A survey of RpLV and RLMV in Washington and Oregon revealed that the two viruses are present at high incidence in northern Washington; whereas the incidence in southern Washington and Oregon, where crumbly fruit is not a serious problem, was considerably lower. BRNV is more common in Oregon and southern Washington.
Poor pollination, tarnished plant bugs, two-spotted spider mites, boron deficiency, and sometimes Botrytis have also been associated with crumby fruit.
Symptoms The virus complex may not produce symptoms on the foliage of many cultivars but may cause crumbly fruit as in Meeker. Many drupelets abort, which causes the fruit to crumble at harvest or postharvest during IQF freezing, resulting in significant reductions of yield and fruit quality. On 'Puyallup', bright-yellow areas along the leaf's main and smaller veins give the leaves a "network" appearance. Severely affected leaves are almost completely bright yellow. In some red raspberry cultivars, faint ring and line patterns develop on leaves. The disease reduces cane growth and fruit yield in 'Meeker' and 'Canby' red raspberry but the major impact is a reduction in fruit quality. In the black raspberry 'Munger', both reduced growth and crumbly fruit occur. Though many cultivars are symptomless when infected with only one of the viruses, 'Autumn Bliss' develops bright yellow leaves and crumbly fruit when plants are infected with RBDV alone. As far as is known all blackberries are symptomless when infected with any one of these viruses, thus can serve as inoculum sources for new fields planted nearby. In blackberry, RBDV in mixed infections with BRNV and/or Blackberry calico virus can cause drupelet abortion and misshapen fruit, though it has been much less of a problem in blackberry than in red raspberry.
- Use certified planting stock.
- Plant resistant cultivars, such as Willamette, Chilcotin, Haida, Comox, Heritage, Cowichan, and Cascade Harvest; however, some strains of the virus may infect 'Willamette' or 'Cascade Harvest'. The cultivar Wakefield has a high level of field resistance.
- Plant in large blocks to slow movement into new plants, especially if fields in the immediate area are infected.
- Isolate new plantings from Rubus fields known to be infected. This requires testing, as many cultivars are symptomless when infected with only one of the viruses.
- Place honey bee hives in the centers of new fields, rather than along the edge, to reduce the risk of bees carrying the virus in from nearby fields that contain infected plants.
- Management of aphid insect vectors is helpful to reduce symptom severity especially 2 to 3 weeks prior to harvest
References Martin, R.R., MacFarlane, S., Sabanadzovic, S., Quito, D., Poudel, B. and Tzanetakis, I.E. 2013. Viruses and virus diseases of Rubus. Plant Disease 97:169-182.
Quito-Avila, D.F., Lightle, D., and Martin, R.R. 2014. Effect of Raspberry bushy dwarf virus, Raspberry leaf mottle virus, and Raspberry latent virus on plant growth and fruit crumbliness in 'Meeker' red raspberry. Plant Disease 98:176-183.