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Rose Black Spot

Q:  What is causing these big, black spots on the leaves of my roses?

A:   This disease is appropriately called “Black Leaf Spot.”  It is caused by a fungus, which can be especially troublesome during wet weather.  Since we are currently experiencing drought conditions you might ask how such a disease can be a problem.  This fungus is spread from leaf to leaf by water and wind and the problem becomes compounded by over-head irrigation when leaves stay wet for extended periods of time.  Most plants, including roses, prefer to be watered directly at the root area.  Not only is this form of irrigation better for the plant it also has other advantages.  Those advantages include reduction of loss of water through evaporation and lower incidents of disease.  Sanitation methods such as removal of diseased plant material from around the base of the plant will also be beneficial. Local garden centers and nurseries sell many varieties of fungicides to help manage this disease.   Remember, fungicides work best as protectants rather than a cure.  Therefore, apply fungicides on new plant growth to protect them from fungal spores.  Remember to always read the label before applying any chemical to your landscape.  You will need to combine your efforts by using chemicals as well as changing your irrigation methods.  For more information see http://edis.ifas.ufl.edu/pp268.