- Rust, rarely fatal, is a fungus marring rose leaves with rusty-brown spots. Black spot, on the other hand, is serious. Black spots, followed by leaf yellowing and defoliation can kill a rose if left untreated.
- Rust and black spot thrive in moist garden conditions. Roses should be planted with plenty of room to grow to maximize air circulation. Watering at ground level keeps leaves dry and free from splashing, which spreads disease spores.
- Both fungi can be treated with regular applications of a fungicidal spray containing chlorothalonil (Daconil), triforine (Funginex) or propiconazole (Banner). Spray the tops and bottoms of leaves, flowers and stems, following the spraying schedule provided in product instructions. Unless a rust infestation is serious, it does not need to be treated.
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