No chemical control is listed. Botrytis blight is worse in dull cloudy weather. The buds rot and infected parts may be covered with grayish powdery mold. Remove infected plant parts. Spray with benomyl.
Powdery mildew causes white or grayish mold.
The disease is worse late in the season and badly infected leaves are distorted and drop. Spray with sulfur or benomyl. Verticillium wilt causes brown or black streaking in the conductive tissue of the stem. Plants wilt and die. Stored roots rot if infected.