Septoria Leaf and Cane Spot

Leaf spot and Septoria cane spot is one of the most common diseases of blackberries

One of the most common diseases of blackberries, leaf spot and septoria cane spot is not usually regarded as destructive. This disease seems to be generally prevalent wherever brambles are grown, and the most of varieties are susceptible. Septoria leaf spot is caused by Mycosphaerella rubi (Septoria rubi). It affects mostly erect and trailing thornless blackberry cultivars. The disease is quite successfully cured. Symptoms are very similar to Anthracnose.
Minute purple dots appear on the leaves about the first of June or later (in southern regions may be early) according to weather conditions. The spots remain small, rarely exceeding 3-4 mm in diameter. The edge of the spot shows a zone of reddish brown and the center is light brown or tan. In the center of the larger spots minute black dots may usually be seen. The disease appears also on the canes of blackberries, but is entirely superficial in nature and probably does no damage. In the fall minute black dots appear on the gray or light tan surface of the bark. In the spring these are especially evident on the old canes and on the ends of branches which have died the previous season.
The pycnidia, the black dots mentioned, are filled with many long slender spores which ooze out during damp weather. These are washed over the surfaces of the neighboring leaves, and probably carried by mist showers to other parts of the patch, where new infections take place.
The fungus winters on the leaves and produces a winter type of spore in the spring. The pycnidia on the canes also produce numerous spores in the spring and these, no doubt, also bring about infection of the new foliage and canes.
Broad-spectrum fungicides applied to control botrytis grey mold (Sclerotiniaceae fungus) generally help to control leaf spot (Captan, Mancozeb, Pristine, e.t.c). Fixed copper or Bordeaux mixture also can be used for treatment, but can cause plant damage in hot weather.