Pest
Management Home Page Dr. John F. Baniecki Powdery mildew of rose ranks second to black spot as a serious disease of rose in the eastern United States. This disease is destructive to roses because young succulent growth is affected. The disease may appear as early as April, as soon as new leaves develop, and becomes well established by mid-May on rambler roses, often preventing blooming. The disease may appear on hybrid teas and floribundas by June, but is more severe on these types in late summer as nights become cooler. The fungus, Sphaerotheca pannosa var. rosae, overwinters in the buds and the canes and the first symptoms of the disease are slight curling of the leaves followed by the appearance of the white, powdery growth of the fungus. Buds may not open, or if they do open, the flowers are abnormal in appearance. The leaves become blistered and have a reddish cast under the white fungus growth. This reddish cast may become almost black in appearance. Powdery mildew is more severe on succulent growth brought about by excessive nitrogen fertilization. |
