There are lots of strongly held opinions about aphids and ways to get rid of them. It seems to me that the most important thing to do is to examine your roses daily, looking most closely at buds and other new growth. And, on finding aphids, to wash them off.
I tend to use spot treatment of aphids with a soapy solution because I get some satisfaction of watching the little insects suffocate as the soapy solution clogs their trachae in a way that plain water does not. They tend to drop from the plant and I feel assured they will never return. But if your whole rose plant is covered with aphids, it's almost certainly better for the plant to spray them off with a high pressure (garden hose with a nozzle) spray of plain water, as soap solutions can cause plants to lose moisture faster than plain water will.
Regarding pesticides, they can seem like a good idea until one considers that most pests such as aphids are food for predators such as praying mantis and ladybugs. When these predators are killed by eating pests treated with pesticides, they can die too. Because the life cycle for pests is so much shorter than it is for their predators, this can mean that the aphids reproduce much faster. With predators gone, they become a problem faster than before pesticides were introduced. Because of this there are cases where the use of pesticides can acually increase the number of aphids in a garden. Many serious gardeners here have serious reservations about using them, especially in some broad, blanketing way.
