Several bugs can be found on a rose bush. Different ones can strike at different times of the year and they can quickly spread to other rose bushes in the same garden, and to neighboring gardens. Rose gardeners need to make visual inspection of the bushes a part of their daily routine or they run the risk of losing flowers, leaves and, in the worse cases, the entire bush.
Japanese beetles (Popillia japonica), also known as the chafer beetle, rose chafer and garden chafer; aphids (Macrosiphum rosae), also known as plant lice; thrips (Anaphothrips obscurus or Frankliniella tritici), also called grass thrips or oat bugs, and the rose leaf hopper are all insects that can do various levels of damage to a rose bush.
Japanese beetles are from a quarter to a half inch in length and are a copper-green color. Aphids are from a sixteenth to an eighth inch long and can be light green, brown, red or black. Thrips are just 1 mm (0.039 of an inch) long, dark brown and have fringed wing tips. Red leaf hoppers are 3 mm (0.118 of an inch) long, wedge shaped and greenish yellow. They will jump when disturbed and prefer floribunda roses.
Japanese beetles will start at the top of the bush and at the outside edges of the leaves. You can spot the tiny black aphid eggs in the spring near the new leaf buds. With thrips, the flowers either will not open or be distorted and have brown, yellow, white or black lines or spots. Rose leaf hoppers are hard to spot. They usually gather on the backside of the leaves, which will curl up, become stunted and turn brown or yellow.
The Japanese beetle can eat not only the whole flowers, but the entire leaf as well, leaving only the stems, and they prefer light-colored roses. Aphids suck the juices out of the new buds in the spring and can kill the whole plant. Thrips ruin the flowers buy sucking out the sap. Rose leaf hoppers suck the chlorophyll and sap out of the leaves, causing them to fall off prematurely.
Birds will eat Japanese beetles. The beetles can also be shaken off the bush into a bucket of soapy water. Planting garlic, catnip or geraniums near the roses will keep the Japanese beetles away. Using a hard spray from the garden hose can knock aphids off the bush. Ladybugs eat aphids and can be bought at most garden centers. Thrips like it hot and dry, so keeping the plants moist, but not wet, can deter them. Remove and dispose of any buds they have attacked. Planting alliums will also keep them away. Spraying the bush with insecticidal soap can kill thrips. Using an insecticide specifically for rose leaf hoppers is the best course of action.