Double blossom or rosette of blackberry is caused by the fungus Cercosporella rubi. Infected buds give rise to multiple shoots. Fruit usually do not develop on infected canes. Some buds develop normally while others are have multiple shoots with short internodes. The photo on the bottom shows the multiple shoots and short internodes.
Bud growth is stunted and pink/white not green (photo on top). Buds on floricanes will either not develop or will be stunted. New primocanes are distorted and abnormally colored (photo on bottom). These symptoms are caused by glyphosphate.
Lack of cane development in spring (go to virus section)