Black spot (
Diplocarpon rosae, Marssonina rosae) is one of the most common and important diseases of roses throughout the world. Black spot will cause a general weakening of the plant so that progressively fewer and fewer blooms are formed if the disease is left unchecked. Spots are nearly circular with fringed or feathery margins and vary in size. Surrounding leaf tissue turns yellow before dropping. Bottom leaves are normally affected first. Conditions that favor the development are 75-85 degrees F, temperatures with relative humidity above 85%, overcrowding and reduced air flow.
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/
One of my favorite evergreen shrubs is now in full bloom. If you get a moment to stop by the Extension Office in Jackson Park you can enjoy the magnificent aroma of Daphne odora, also known as winter Daphne. Each year we have many people stop in to ask the name of the fragrant shrub outside our door that is blooming in early March. It is not something one can ignore.
