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Beginner

Scientific Name:Didymella applanata

Identification

• Affects blackberries, black and red raspberries.
• Infections begin on the edge of older leaves and advance to the midvein and then into the bud.
• A dark brown v-shaped lesion develops at the base of the buds.
• Overwintering lesions become silvery grey.
• Infection causes weak or delayed growth of infected buds and increased winter injury.
• In the spring, some infected buds will develop into lateral shoots that appear to be healthy, while others will fail to grow.
• Infected leaves will shed prematurely.

Often Confused With
Cane Botrytis
Anthracnose

Period of Activity
Primary spores (ascospores) are discharged from old fruiting canes from May to August. Secondary spores (conidia) are also produced. Conidia splashed around in July and August will likely cause the most damage. The lowest leaves and spurs are infected first and the infections move up the cane as the season progresses.

Scouting Notes
Check overwintering canes for silver v-shaped lesions at leaf nodes. Check primocanes in mid-late summer as older leaves begin to senesce. Infections on the lower leaves are less serious than infections on the middle portion of the cane where crop losses can be greater. Examine mature leaves for browned v-shaped lesions, and examine primocanes for dark brown or purple lesions v-shaped lesions at the base of leaf spurs.

Thresholds
None established.

 

Advanced

Scientific Name: Didymella applanata

Identification
Spur blight infections begin on the edge of older leaves. The infection advances to the midvein and then into the bud. A dark brown v-shaped lesion develops at the base of the buds. Overwintering lesions become silvery grey. Spur blight infection causes weak or delayed growth of infected buds and increased winter injury.

Spur blight infections reduce yields by disturbing the translocation of nutrients to and from the leaves. Infected buds, or spurs, that would normally produce new fruiting laterals in the next growing season, may be weakened, damaged, or killed. Yield losses may be severe if there are few fruiting laterals in the following year.

Often Confused With

Cane Botrytis
Lesions from cane botrytis appear light brown, and extend beyond a single leaf node, while  spur blight lesions are v-shaped.

Anthracnose
Anthracnose lesions are small, circular/oval and purple with a grey centre. They form all over the cane, on leaves, on petioles, and even fruit. Spur blight lesions, are dark brown, and v-shaped. They are found on infected leaves and on canes at the base of leaf nodes.

Biology
Spur blight is caused by the fungus Didymella applanata. It affects blackberries as well as black and red raspberries. Summer bearing varieties such as Tulameen and Qualicum are especially susceptible.  
D. applanata overwinters as mycelium, pseudothecia and pycnidia on infected canes. Once temperatures and precipitation increase in spring and early summer, pycnidia, or fruiting bodies, produce conidia. These are dispersed by strong, splashing rain to leaves, where infection occurs.   The fungus spreads from the outer leaf margin to the midvein, causing a brown v-shaped lesion. The disease advances from the leaf via the petiole into the node. Dark brown to purple, v-shaped lesions develop at the base of the bud and spread downward.  

Young leaves are resistant to spur blight infection. Mature and slightly senescent primocane leaves are very susceptible to infections, especially when light is limited at the base of the canes in the summer. The first spur blight lesions usually appear on low nodes of primocanes around June or July. New buds may not form from infected nodes, especially if temperatures are mild in the fall. If bud scales become infected, they may break and dry out which can cause the death of buds in the winter. 

Period of Activity
Primary spores (ascospores) are discharged from old fruiting canes from May to August. Secondary spores (conidia) are also produced. Conidia splashed around in July and August will likely cause the most damage. The lowest leaves and spurs are infected first and the infections move up the cane as the season progresses.

Scouting Notes
Check overwintering canes for silver v-shaped lesions at leaf nodes. Check primocanes in mid-late summer as older leaves begin to senesce. Infections on the lower leaves are less serious than infections on the middle portion of the cane where crop losses can be greater. Examine mature leaves for browned v-shaped lesions, and examine primocanes for dark brown or purple lesions v-shaped lesions at the base of leaf spurs.

Thresholds

None established.

Management Notes

• Space rows at least 2.5 m apart. Keep rows narrow by limiting the width of plants in the row to 30-45 cm. This will allow for good air movement, encourage drying and reduce the number of infections.
• Avoid excessive use of nitrogen fertilizer because it promotes abundant foliage growth,  an ideal environment for spur blight infections to occur.
• Prune fruiting canes and diseased primocanes immediately after harvest.
• Early fungicides applied at green tip are important  to reduce overwintering inoculum. Further applications can be made at the green fruit stage and post-harvest. Fungicides used for control of botrytis fruit rot may also help to suppress spur blight as outlined in the OMAFRA Publication 360: Fruit Crop Protection Guide (Chapter 3 Berry Crops).