Roses bushes grace gardens around the world with their fragrant blossoms and abundant green foliage. Numerous bugs infect rose bushes. The insects will normally never kill the bush but simply render it unattractive and weaken its overall health. Pests weaken the plant and place undue stress on the rose bush's system, making the plant more prone to winter or drought injury.
Aphids (Macrosiphum rosae) live in large colonies on rose bushes, particularly new growth and buds. The insects attach their mouths to the plants tissue to consume the sap. That causes leaves and buds to distort. The insects appear as tiny red, green, brown or black spots on the bushes foliage. Aphids secrete a honeydew substance that can encourage mold spores to grow, which often causes fungal infections.
Rose scales (Aulacaspis rosae) attach themselves along the stems and underside of the rose bush's leaves to suck the plant's sap. They form protective scales over their tiny bodies. The scales appear as either brown or grey dots. The insects spread quickly. The new foliage and buds of the rose bush will begin to wilt and die if the infestation is not controlled.
Newly pruned canes of the rose bush are susceptible to cane borer infestations. Cane borers are the larvae of sawflies and carpenter bees. When the rose bush is pruned, the larvae makes its way to the wounded end of the cane to bore into it using their powerful mouths. The foliage of the bush will wilt, leaves turn yellow, and the overall health of the bush will be seriously compromised.
The larvae of the rose midge (Dasineura rhodophaga) feeds on the new growth of the rose bush. The buds turn black and fall from the bush. The buds that survive will appear deformed or fail to open. The larvae are difficult to see with the naked eye and most gardeners must simply assume they have an infestation from the rose bush's symptoms. The adults appear mosquito-like and only land on the rose bush long enough to lay its eggs.
Spray aphids or rose scale from the rose bush using a strong burst of water from a garden hose. Rub the scales away while hosing the plant's stems and foliage. Insecticidal oils work well to suffocate rose scales. Cane borers are preventable by applying a tree sealant or glue to the pruned ends of the plant after removing the infected cane. Use an insecticide that contains cyfluthrin for rose midge control, according to the Pittsburgh Rose Society.