Answer: The blooms on roses will last longer under ideal weather conditions (cool, cloudy but dry, not windy) but may fall quickly if the weather does not cooperate. A lack of soil moisture or excessive heat can cause them to fall rather quickly. The tiny red spots may be rust, a fungal problem. You might try removing the infected leaves and spraying with a neem-based product according to the label instructions to try to control it. Also, make sure the rose is in a location with good air circulation and avoid overhead watering, especially in the evening.
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