Plantations can crop productively for more than 15 years, but this is only possible if the planting stocks, soils and general environment are free from viral, bacterial and fungal pathogens and certain pests. The most common reason for replanting is degeneration caused by infection with pests and diseases, particularly virus pathogens that cannot be eliminated once plants become infected and which can cause very severe symptoms in mixed infections. Hence, in considering the factors that dictate whether a plantation will be long-lived and productive, it is important to plant healthy propagation material from a recognised certification scheme and to manage pests (particularly those that transmit virus pathogens) and diseases throughout the life of the plantation.
Raspberries and their hybrids are subjected to attack by a wide range of pests and diseases and substantial losses in yield and fruit quality occur throughout Europe. Currently, many of the pests and diseases can be adequately controlled by use of chemicals applied to the crop. However, disease control strategists face the withdrawal of approved products, a restriction in the number or times of application of the control products and fungicide resistance in some pathogens.
Phytophthora root rot and botrytis grey mould are by far the most serious of the fungal diseases in Europe, resulting in extensive losses and significant levels of chemical application. Other fungal pathogens of concern include those causing cane and foliar diseases. Virus infections in Rubus crops are particularly important because mixed infections with different viruses can lead to very damaging symptoms and disease. Viruses are spread within plantations by pollen transfer, nematodes and aphids, but at present aphid-transmitted viruses are probably causing the most important virus diseases in the UK. There are effective sources of resistance to some aphids in certain cvs, although resistance-breaking aphid biotypes have developed. Virus spread can be limited by insecticide use to kill aphid vectors, but in the longer term natural resistance to aphids or virus are more promising routes to follow. Of the raspberry pests, aphids (because of the viruses they transmit) and raspberry beetle (because of the fruit quality problems they induce) are probably the most important.
The above problems are increasing pressure on plant breeders and pathologists to identify and incorporate new sources of host resistance into commercially acceptable genotypes.
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