Purple blotch—Septocyta ruborum
Purple blotch causes dark green irregularly shaped lesions to form on canes of blackberries. Lesions
may become brown or purple with a red margin. Small, black pycnidia develop in the center of the mature
lesions. Canes eventually become girdled and, in severe cases, will die. Purple blotch does not cause
leaf spots to form.
The fungus that causes purple blotch survives on infected
canes. Spores are dispersed by splashing water or rain. Avoid
overhead sprinklers. Prune to provide good air circulation. Control weeds to reduce humidity.
Trellis canes by
early September to reduce winter injury. Use an alternate-year
fruiting program, where canes are trained up as they grow.
After harvest and before fall rains, prune out and destroy
old wood. Fungicides such as Bordeaux or a fixed copper
fungicide may help provide control throughout the growing season. Spray fixed coppers after harvest. Use fixed copper or Bordeaux before fall rains begin and spray again with fixed copper in spring at budbreak.
blotch lesions on canes