Destroy all fallen leaves and prune infected canes severely during late winter. A white powdery growth occurs on leaves, buds and twigs causing them to be distorted and dwarfed. Young, tender growth is most susceptible. The disease is more likely to occur during cool, dry conditions and can spread rapidly since a complete life cycle can occur in 72 hours. Thousands of spores are produced on a single plant with each having the ability to cause disease.
Varieties differ in their susceptibility.
Use an appropriate fungicide during times when disease pressure is high. These often girdle the stem and tissue past the point of infection is killed. Prune infected limbs and twigs being sure to cut well below the diseased tissue. Disinfect shears in formaldehyde or chlorine solutions between each cut. Keep plants free of other diseases.