Gardening Articles: Care :: Pests & Problems
Black Spot Resistant Roses
by Susan Littlefield
The Earth-Kind® program was started at Texas A&M University to support environmental landscape stewardship. Part of this program includes research and trials to identify regionally adapted cultivars of roses that will thrive without the use of chemical pesticides and fertilizers and that tolerate reduced irrigation.
One of the most difficult problems for rose growers to deal with is black spot, a fungal disease that causes black spots on the upper leaf surfaces, progressing to yellowing and dropping of infected leaves. Untreated infections gradually weaken plants, resulting in fewer and fewer flowers.
Recently, as part of this program, researchers evaluated 73 rose cultivars for susceptibility to three races of Diplocarpon rosae, the fungus that causes black spot. Young leaves were inoculated with the fungus and susceptible reactions measured. Nine cultivars were identified as being completely resistant to all three races of the fungus. These were Brite Eyes™, 'Grouse', Home Run® (pictured), Knockout®, Paprika™, Pearly Cream™, Pink Knockout®, Rainbow Knockout®, and Yellow Submarine™. These cultivars are all good choices for gardeners interested in growing roses sustainably.