Raspberry viruses

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.

Raspberry viruses

Raspberry viruses

Quick facts

Common name Raspberry viruses
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 sometimes 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.

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.

Symptoms

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 much less serious, but the mites cannot usually be seen without the aid of a microscope. Plants affected by the mite usually grow to their normal height and produce satisfactory crops, unlike the gradual stunting and yield loss caused by virus infection.

Control

Non-chemical control

  • 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)

Chemical control

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.

Biology

Plant viruses are minute parasitic entities consisting only of a nucleic acid core and a protein coat. They cannot reproduce except in the cells of the host plant, where they 'hijack' the cell's synthetic mechanisms to produce more virus particles, causing a variety of symptoms in the process.

The names of many raspberry virus diseases are based on the symptoms seen in affected plants, rather than the name of the causal virus. For example raspberry mosaic, probably the most common and damaging virus disease, can be caused by at least five different viruses (the more important being Rubus yellow net virus and Raspberry leaf spot virus).

One disease of raspberries, called Rubus stunt, is caused by a phytoplasma (these share some characteristics of both viruses and bacteria).

Viruses and phytoplasmas require a vector to transfer them between plants. The vectors of raspberry viruses include:

  • Aphids: All of the viruses causing raspberry mosaic are aphid-transmitted
  • Soil-borne nematodes (eelworms): The most common is Arabis mosaic virus
  • Leafhoppers: These are common vectors of phytoplasmas, including Rubus stunt

Some viruses can also invade the seed of raspberries and one, Apple chlorotic leaf spot virus (which causes a disease called raspberry bushy dwarf) can spread from plant to plant in infected pollen grains.

Some of the viruses affecting raspberries (e.g. Arabis mosaic virus, Cucumber mosaic virus) have very wide host ranges, and can affect a large number of garden plants and even weeds.


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