Answer: Sounds as though your rose has powdery mildew, a fungal disease. It is quite common on all types of roses. Try using a homemade baking soda/oil spray: mix 1 tsp. baking soda and 2.5 tsp. summer oil (a lightweight horticultural oil) in 1 gallon of water. Spray this once per week, covering both upper and lower leaf surfaces. A commercial organic alternative is Soap Shield Fungicidal Soap from Gardens Alive (www.gardensalive.com). Also, keep your roses healthy through proper care, since they'll be more resistant to disease. Provide full sunshine, good air circulation all around the plant, and ample moisture. You can remove the leaves affected with powdery mildew so it won't spread to healthy leaves.
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