Raspberry spur blight is a fungal disease of raspberries causing purple patches on canes. It rarely kills raspberries, but can reduce yield severely by weakening the canes and killing buds.
What is spur blight?
Spur blight is a disease of raspberries caused by the fungus Didymella applanata. It appears from late summer and persists on infected canes until the following year.
It mainly affects raspberries and occasionally loganberries. It is particularly common during wet seasons.
You may see the following symptoms:
- Conspicuous purple patches on new canes in late summer, centred around the buds. They increase in size, spreading up and down the cane from the point of infection
- As autumn and winter progress the patches become less distinct, fading to a pale grey or silvery colour. Fruiting bodies of the causal fungus may be visible as tiny black spots on the affected areas
- Many of the buds on canes, infected the previous year, fail to grow in spring or produce weak shoots that soon die. These canes appear bare and unthrifty compared to their healthy counterparts
- Avoid overcrowding by thinning out any young canes that are not required. This should be done as early in the spring as possible
- Avoid the over-application of nitrogen
- If spur blight develops, cut out and dispose of badly affected canes
- Choose resistant cultivars. The cultivars ‘Glen Lyon’, ‘Glen Moy’, ‘Glen Rosa’, ‘Julia’, ‘Leo’ and ‘Malling Admiral’ have some resistance to spur blight
The fungicide, copper oxychloride (Bayer Garden Fruit and Vegetable Disease Control) can be used on raspberries. It is recommended for cane spot control, but may also have useful activity against spur blight.
Spray canes in spring, avoiding the flowering period. If it is necessary to spray during flowering, do so in the evening to avoid harming pollinating insects.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)
Didymella applanata produces two spore types. The first type starts the infection on the new canes in the spring, while the second causes further spread during the summer. Infection usually occurs via the leaf stalks or buds, and is favoured by wet weather.
Overcrowded canes, and those that have received too much nitrogen, are more prone to attack.