Here are some of the most common insect pests of roses and how to recognize them.
Aphids
. Small, pear-shaped insects that congregate on new leaves and flower buds, sucking plant juices, leading to plant damage and distorted growth. Aphids come in many colors and secrete a sticky, sugary substance called honeydew. The honeydew often turns black as it becomes infected with sooty mold, which makes your roses look even worse. If that's not enough, honeydew also attracts ants, which feed on beneficial insects, which further complicates problems. Eliminate the aphids and you'll also get rid of the sooty mold.
Beetles . A number of related beetles, including Japanese beetles, June beetles and rose chafers, are serious pests of roses. One or the other is common in most parts of the country.
Rose Midge
. If your roses seem otherwise healthy but the flowers just don't open properly, its probably caused by the rose midge. These nearly invisible insects scrap new growth particularly flower buds, causing them to shrivel and turn black.
Scale . If stems of your roses are gray and crusty and occasionally die out, it may be one of several species of scale.
Spider Mites
. These tiny spider-like pests are just about invisible to the human eye, but you can definitely see the damage they do. Spider mites suck plant juices from rose leaves, causing them to turn yellowish with a silvery sheen, and often drop off. They usually congregate on the undersides of the leaves, and if the infestation is bad enough, you'll see the webbing there. Another way to test for mites is to hold a piece of white paper under a branch and shake it. If you see any tiny specks fall on the paper those are mites. Spider mites are most common in hot dry weather and on dusty plants.
Thrips . Another tiny pest that you'll have trouble seeing with the naked eye, thrips feed on rose petals, causing them to be deformed and discolored. Buds often fail to open properly.