Answer: Powdery mildew is a fungal disease that attacks plants when environmental conditions are right (warm days, cool nights, some humidity) and air circulation is poor. You can help avoid powdery mildew by giving plants the required exposure to sunshine, and plenty of elbow room so there's good air circulation all around them. Your roses need at least 8 hours of direct sunlight each day to keep them healthy.
Fungicides generally recommended for powdery mildew control include: Triadimefon (Bayleton, Strike); Triforine (Funginex), Thiophanate-methyl (Cleary's 3336, Domain). Propiconazole (Banner) and sulfur fungicides. Frequently used fungicides for black spot include Folpet (Phaltan), Captan, Mancozeb (Fore), Chlorothalonil (Daconil) and Triforine (Funginex). For rust, Triforine (Funginex), Mancozeb (Fore) and Chlorothalonil (Daconil) are effective. Follow labeled instructions regarding dose and frequency of application. It is important to spray on a regular schedule.
Follow all labels carefully, and be sure and spray both surfaces of all leaves thoroughly.
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