These precautions reduce overwintering fungi. A fungicide program should start in the summer just before leaves become spotted. From then until frost, the leaves may require a protective fungicide coating. When the leaves are growing rapidly or during rainy weather, it may be necessary to spray the plants two times a week. However, if growth is less rapid and rains are less frequent, spraying at 7 to 10 day intervals is usually sufficient.
Proper timing is as important as the chemical spray.
A preventive spray program can include the chemicals listed in table 1 . Powdery Mildew is caused by the fungus Sphaerotheca pannosa . This disease can cause young leaves to curl and turn purple. Young canes may be distorted and dwarfed. If seriously infected, they can die.