Why Do My Blackberry Canes Have Purple or Brown Spots?

Small, circular or oval spots — initially purple, developing into grey-white centres with purple borders — appearing on blackberry canes in spring and early summer are the classic symptom of cane spot disease, caused by the fungus Elsinoe veneta. The same pathogen also causes spots on leaves (small purple dots) and can affect fruit stalks. Severe cane spot weakens the overall cane and can cause dieback of the lateral shoots that carry the fruit.

Identifying cane spot

Cane spot lesions start as small purple spots on the cane surface in April and May. The spots enlarge to 5–10 mm, developing white or grey centres with well-defined purple or dark red borders. Later in the season, tiny dark fungal fruiting bodies may appear in the centres of the spots. On leaves, cane spot produces much smaller spots — often just 1–2 mm, purple-bordered, appearing in late spring. On fruit stalks, spots can girdle the stalk and cause individual fruit clusters to fail.

Control: post-harvest cane removal

After the current season's fruiting canes have been harvested, cut them back to ground level and remove them from the site. These old canes carry the highest concentrations of overwintering fungal material and removing them reduces the inoculum source for the following season. Do not leave old fruited canes tied in through winter as they do on untended plants.

Fungicide treatment

Copper-based fungicide applied just before bud burst in early spring (February–March) suppresses the early-season infection phase. A second application after flowering has finished reduces summer spread. Conventional fungicides containing myclobutanil are more effective but should not be applied near harvest unless pre-harvest intervals are observed.

Avoiding spread

Disinfect tools (secateurs, loppers) between plants when pruning — cane spot can be spread mechanically on cutting tools. This is particularly important when moving between an infected and a healthy plant.