Root rot diseases have always been a problem in North America but were not regarded as a problem in Europe until the 1980s when Phytophthora root rot emerged as a major problem of raspberry with outbreaks in the U.K. This disease is now the most destructive disease of raspberries. Several Phytophthora species are known to infect red raspberry, but the most prevalent in serious disease outbreaks is Phytophthora fragariae var rubi. All parts of the plant below or at ground level can be infected, and affected canes die in the first year of growth or their buds fail to emerge at the start of the second growing season. Alternatively, emerged laterals wilt and die at any time from emergence until late in fruiting. Phytophthora is a soil-borne fungus and viable resting spores can remain in soil for many years. Thus, replanting into contaminated soil can result in the continuation of the disease and spores are readily spread in soil water so the area of infected plants will expand. The prevention of new outbreaks can be achieved by ensuring that the planting material is free of disease, combined with avoiding fields with known or recent root rot problems, or planting in soil where raspberries have never been grown previously and the fungus is not likely to exist.
There are some potential sources of resistance in red raspberry cvs 'Latham' and 'Winkler Sämling', and species material such as R. strigosus and R. ursinus. Genetic resistance through plant breeding offers a feasible and effective method of control, but because of the time involved in combining resistance with other desirable traits, e.g. fruit size and quality, it has not yet had the anticipated impact in commercial production. More research to find resistance genes and breeding is required and is in progress at SCRI.
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| Root rot affected plants showing typical 'shepherd's crook' symptoms on affected primocane |
| Root rot affected plants showing symptoms and death of mature cane with lack of primocane growth |
| Aerial photograph of a field with a large spreading patch of root rot affected plants |
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