Submitted to: Proceedings of the North American Bramble Growers Association Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: March 22, 2004
Publication Date: May 22, 2004
Citation: Smith, B.J. 2004. Rosette (double blossom) of blackberry. Proceedings of the North American Bramble Growers Association Annual Meeting. pp. 27-30 Technical Abstract: Rosette is a severe disease of blackberries in the southeastern United States which often limits commercial production if it is not controlled. The causal fungus, Cercosporella rubi, infects primocanes in the spring or early summer, but disease symptoms are not evident until the following year when new growth begins on the fruiting canes. Most thorny, erect blackberry cultivars adapted to the area are very susceptible to rosette. Rosette can be controlled through a combination of cultural practices and chemical treatments including planting resistant cultivars; eradication of infected wild blackberries near the field which are often the initial source of infection in commercial fields; pruning out infected rosettes; and mowing severely infected plantings. In fields where the disease is so severe that harvest is not feasible, the plants may be mowed before harvest. Yield from mowed fields will be drastically reduced the following year. Except along the Gulf Coast where the growing season is longest, most cultivars should not be mowed more than once every three or so years. However, the primary control of rosette is the application of fungicides to reduce the spread of the rosette fungus from infected flowers to primocanes. Fungicide applications should begin when infected flowers open and continue as long as rosette infected flowers continue to bloom. Among the fungicides registered for use on blackberries, Abound, Switch, and Pristine, are the most effective for rosette control. Fungicides will not stop symptom development on current year's fruiting canes. The goal of fungicide treatments is to prevent infection from occurring on primocanes.