Aphids are the most common of rose pests and are usually green, reddish or brown in color. They feed on the sap of the tender new growth at the tips of the canes causing growth and flowers to be stunted. A hard spray of water from the hose will knock them off and often they will not be able to return to the plant. You can also remove them with your fingers by stroking the tips with your thrumb and forefinger.
Ladybugs love to dine on aphids and can devour hundreds in a short time.
If the infestation is really bad then the plant can be weakened and an insecticide spray will be needed.