Although the spots are unsightly, the more serious effect is from premature defoliation which reduces plant vigor. To control black spot, a regular, preventive fungicide spray program must be followed throughout the growing season. This spray schedule needs to begin as soon as new leaves begin appearing after pruning in late winter. Fungicides containing benomyl, captan, mancozeb, triforine, chlorothalonil, thiophanate melhyl or thiophanate methyl plus mancozeb are recommended. Be sure to follow the label recommendations.
Powdery mildew appears in early spring and lale summer when nights are relalively cool.
Symptoms include a white coating of the fungus growth which covers young buds, resulting in no bloom or distorted leaves. Leaves curl slightly or may become blistered. This disease occurs on leaves, buds and canes, causing a stunting and twisting of new growth. Leaf rust is another rose disease prevalent in Louisiana. It is recognized in the early stage by the appearance of rough, circular, bright orange spots on the underside of leaves and on stems.