Raspberry cane blight is a common and serious fungal disease of raspberries, causing extensive die-back of canes.
What is cane blight?
Cane blight is a disease of raspberries caused by the fungus Leptosphaeria coniothyrium, which infects the developing canes through wounds, causing them to die back. The disease is often associated with attacks by raspberry cane midge. You will see attacks from mid-summer.
Blackberries can also be affected, but on them the disease is of little significance. The fungus causing cane blight can also cause a canker disease of roses and a root rot of strawberries.
You may see the following symptoms:
- During summer, leaves on fruiting canes wither and the canes die
- The bases of the canes become dark brown, and the bark may split. The wood becomes very brittle so that the canes snap off easily at the base
- Tiny, black fungal fruiting bodies, just visible to the naked eye, are produced on the infected wood
- Handle canes carefully to avoid unnecessary damage
- Ensure that they are well spaced so that air circulates and the canes dry out quickly after rain or heavy dew
- Avoid plant stress by providing appropriate soil conditions, for example by improving drainage on heavy soils and mulching around the canes to prevent the soil drying out during periods of drought
- Prune only during dry periods
- Where the disease develops, cut out and dispose of any affected canes. Cut back to below soil level and disinfect the secateurs between cuts
- Do not plant raspberries or strawberries in an old raspberry bed without first changing the soil
- The raspberry cultivar ‘Julia’ has some resistance to cane 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 cane blight. Protect against wound infection by making one or more applications to the base of the fruiting canes in spring and early summer.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)
Spores are produced by the tiny black fruiting bodies and are splashed by rain and infect the canes if they remain wet. A second type of fruiting body is produced on old canes in spring, releasing spores that can be carried for long distances on the wind.
Infection invariably occurs through a wound to the cane. The wounds can be caused by a number of factors, including pruning damage and frost cracks. The fungus invades frequently through areas of feeding damage caused by the raspberry cane midge and in this case, the disease is often referred to as midge blight.
Poor soil conditions, such as waterlogging, weaken the plants and make them more susceptible to attack. The fungus is able to survive for some time in the soil on buried raspberry wood.