Maintaining a healthy bed of raspberry plants is often difficult due to their susceptibility to virus infection. Many different viruses can cause a decline in vigour and yield. The symptoms produced by virus infection can be very variable.
Scientific name Various
Plants affected Raspberries, blackberries and hybrid berries
Main symptoms Yellow or pale green spots, blotches, mottles or mosaics on the leaves. Stunted growth and yield loss
Caused by Viruses
Timing Seen mainly in mid- to late summer and autumn
What are raspberry viruses?
Raspberry viruses are virus diseases affecting raspberries and ocassionally other cane fruit such as blackberries and hybrid berries. Plant viruses require an agent known as a vector to introduce them into the plant – most raspberry viruses have aphids (greenfly) or soil-dwelling nematodes (eelworms) as their vectors. Some can be transferred via pruning tools and in seed.
There are a large number of viruses that infect raspberries, either singly or in combination. Often symptoms are worse with multiple infections.
Raspberry viruses found commonly in the UK include:
- Black raspberry necrosis virus
- Raspberry bushy dwarf virus
- Raspberry leaf blotch virus
- Raspberry leaf mottle virus
- Raspberry vein chlorosis virus
Other viruses occurring in the UK, but less commonly encountered, include:
- Raspberry yellow net virus
- Raspberry chlorotic mottle virus
- Raspberry ringspot virus
Other viruses historically reported in raspberries include Tomato blackring virus, Strawberry latent ringspot virus and Arabis mosaic virus, but it is unknown whether these can still be found affecting the crop in the UK.
Any planting of raspberries is likely to decline over time as result of virus infection. The key is to start with virus-free planting material, and to recognise when the effects of virus infection make it worthwhile to replace the plants. Typically, plants need replacing every 7 to 12 years.
The symptoms of infection by raspberry viruses are extremely variable, as they depend on a range of factors such as the virus or viruses present, the raspberry cultivar affected and the environmental conditions. However, you may see the following symptoms:
- Yellow or pale green spotting, blotching, mottling or flecking of the leaves
- Yellowing along the leaf veins
- Downward curling of the leaf margins
- Puckering or crumpling of the leaf blade
- Proliferation of weak, spindly shoots
- Stunted growth and reduced fruit production
- Dry, ‘crumbly’ fruit
- Death of canes
N.B. Yellow blotching and distortion of leaves can also be caused by the raspberry leaf and bud mite (Phyllocoptes gracilis). This is usually much less serious, but the tiny mites can't usually be seen without the aid of a microscope. Plants affected solely by the mites will often grow to their normal height and produce satisfactory crops, unlike the gradual stunting and yield loss caused by virus infection. However, in some cases raspberry leaf and bud mites will also transmit Raspberry leaf blotch virus to a plant, in which case more severe symptoms may develop.
- Always buy plants that are certified as virus-free. It is unwise to accept gifts of plants from established plantings, as these are very likely to be carrying virus infection
- Destroy plants as soon as yields start to fall. Plant replacements in a new site. If only one or two plants show symptoms then removing these may slow the spread of infection through the planting
- Control weeds, which may act as alternative hosts for some of the viruses affecting raspberries
- If possible, avoid replanting raspberries on the same site. Since it is not practical to determine which virus is present on the basis of symptoms (as these are so variable), it would be prudent to assume that some of the viruses spread by nematodes may be involved. These will persist in the soil and infect new plants. Unfortunately, this may involve dismantling and re-erecting fruit cages
- Cultivars vary in their resistance to the various viruses. However, the use of resistant cultivars is impractical if the virus responsible has not been identified (which can only be done with certainty by expensive laboratory tests)
There are no chemicals available for the control of virus diseases. Use of insecticides to control the aphid vectors of some viruses is not possible as those products available to gardeners lack the necessary persistence.
Plant viruses are extremely minute infectious particles consisting of a protein coat and a core of nucleic acid. They have no means of self-dispersal, but rely on various vectors (including humans) to transmit them from infected to healthy plants. Once viruses penetrate into the plant cells they take over the cells’ nucleic acid and protein synthesis systems and ‘hijack’ them to produce more virus.
Viruses are frequently transmitted through propagated material but, depending on the virus, can also be transmitted via insect or mite vectors, pollen, mechanical transfer via contaminated hands and tools, or nematode vectors in the soil. Some viruses can be transmitted via seed, but generally these are a minority and therefore with many plants seed propagation is often a useful way to ensure virus free plant material.
Raspberry viruses are transmitted in a number of ways:
The large raspberry aphid (Amphorophora idaei) transmits Black raspberry necrosis virus, Raspberry latent virus (presence in UK unknown), Raspberry leaf mottle virus, and Rubus yellow net virus.
The small raspberry aphid (Aphis idaei) transmits Raspberry vein chlorosis virus.
The Raspberry leaf and bud mite (Phyllocoptes gracilis) transmits Raspberry leaf blotch virus.
Transmission of Raspberry chlorotic mottle virus is still to be determined, but may be by various insects, by pollen and by seed.
Raspberry bushy dwarf virus is pollen and seed transmitted.
Arabis mosaic virus, Raspberry ringspot virus and Strawberry latent ringspot virus are transmitted by soil-dwelling nematodes and by seed. Raspberry ringspot virus is also pollen transmitted.
Some of these viruses can also be transmitted on tools and hands.
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