Cercospora leafspot (Cercospora puderi, Cercospora rosicola) is characterized by the appearance of numerous tiny maroon to purple oval spots scattered randomly across the leaf surface. Later the center of the spot turns tan to gray in color while the margins remain maroon to dark purple. Heavily spotted leaves will turn yellow and prematurely shed. This infection can be easily confused with Blackspot. Same weather conditions that produce Blackspot will provide optimal growing conditions for Cercospora.
A homeowner may use a fungicide labeled for control of Blackspot to control both of these fungal infections. Fungicides, such as Daconil and Immunox, which are recommended as weekly treatments for blackspot control, should also provide good protection from Cercospora leaf spot when applied on the same schedule.
The University of Tennessee has been conducting a no-spray rose trial for the last two years. A total of 136 cultivars were evaluated for their resistance to black spot and cercospora leaf spot in 3 test locations across the state. Below you will find a listing of the most resistant cultivars of shrub roses. If you would like a full listing of rose cultivars tested, please contact me for a handout.
o Carefree Sunshine (Yellow)
o Hansa (Mauve)
o Homerun (Flame Red)
o Knockout (Cherry Red)
o Palmengarten Frankfurt (Mauve Pink)
o Pink Knockout (Pink)
o Wildberry Breeze (Mauve)
Information provided by Alan Windham, University of Tennessee Extension Service.
American Rose Society http://www.ars.org/