Latin name: Septocyta ruborum
Reason for Concern:
1) A concern in Marionberries, but can affect all varieties.
2) blackberries and hybrid berries.
2) The disease can girdle and kill canes in cold, wet winter, warm, wet spring and summer.
Dark green, irregularly shaped lesions appear on canes late in the growing season. In winter and spring, lesions turn purple with a red margin. Areas 0.5” to 2” long develop cankers and girdle canes. Severely affected canes die in spring. Small, black, fruiting structures are in the lesion's center. Leaf spots do not develop.
Causal fungus is similar to Septoria rubi, which causes leaf and cane spot. Symptoms will not develop unless a chilling requirement is met. Spores from infected fruiting canes fall on primocanes from April to mid-August, during periods of rainfall or overhead irrigation. Most spores fall at 70 degree F temperatures. Spores do not require a wound to cause infection. Even though primocanes are infected, no visual symptoms occur until after winter. Cold, wet winters result in the most lesions. In favorable conditions, (cold, wet winter; warm wet spring/summer) lesions grow larger until they cover large areas of canes and prevent water from moving up canes, causing canes to dry up.
- Marionberries are particularly susceptible to purple blotch, but all blackberries can be affected.
- Symptoms of purple blotch will only develop if a chilling requirement is met.
- In early spring, prior to primocane emergence, purple blotch will be observable as dark lesions with a red, purple, or yellowish margin.
- Later in the growing seasons, look for dark green, irregularly shaped lesions.
- Lesions will have a small black fruiting structure (pycnidia) in their center.