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.

Symptoms

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 dots 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

Control

Non-chemical control

• 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

Chemical control

No fungicides are available to home gardeners for the control of raspberry spur blight.

Biology

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.