Identification and Control Methods of Rose Powdery Mildew: A Detailed Guide

Symptoms: The pathogen infects rose leaves, flowers, and young shoots. In early spring, both the upper and lower surfaces of leaves unfolding from diseased buds are covered with a white powdery substance. The leaves become wrinkled, curled backward, and thickened, then gradually dry up and die, becoming the primary source of infection. When leaves are infected during the growing season, small white powdery spots first appear, then gradually expand into circular or irregular powdery mildew spots; in severe cases, the powdery spots merge into continuous patches. When young shoots and petioles are affected, the lesions enlarge slightly and the internodes shorten. Flower buds become covered with a powdery layer, shrink, and dry up. Mildly affected flower buds open into deformed flowers.

Control measures: Improve ventilation and light penetration, apply more phosphorus and potassium fertilizer, and apply nitrogen fertilizer appropriately. During the dormant period, spray with a 5 degrees Baume lime sulfur mixture solution. When the disease occurs, spray with a 25% Fenarimol wettable powder solution diluted 1500-2000 times for control.