Roses, a staple of Valentines Day and a symbol of affection and love, are arguably the most popular flower in the landscape. In 1986, the popularity of the rose lead President Regan to declare the rose as the United States national flower. Unfortunately, the rose is also a favorite food of the aphid, resulting in twisted leaves and misshapen blooms. Aphids can be easily controlled, however, without resorting to inorganic pesticides that may harm beneficial insects.
Aphids are small, rounded insects roughly the size of a pin-head. Their pear-shaped bodies are soft and usually green, but they can be yellow, black, pink or red. Some varieties have wings. Aphids of all types feed on tender buds, leaves and other new growth by sucking the moisture from a plant. Usually found in clusters, aphids look like tiny herds of destructive cattle, grazing on vulnerable leaves. Aphids keep their heads lowered to the plant, sucking the moisture and producing honeydew, an excretion favored by ants.
When aphids attack young leaves or buds, the plant tissue is damaged. The damaged areas cause the growing leaf to become misshapen, and buds open into warped blooms. Although aphids will rarely kill a plant, they do weaken the plant, leaving it open to disease. Aphids will also carry viruses from one host to another. After leaves have become twisted, the aphids often congregate in the sheltered areas. Because aphids prefer new growth, a slow-release fertilizer should be used to prevent large flushes of tender, aphid-attracting leaves.
Control with Predators
Ants that "farm" aphids for the honeydew will prevent predatory insects from naturally controlling the pests, and so any ants running up and down rose canes must be stopped. Sticky traps placed around the base of the affected rose will trap the ants, allowing the other insects to gain a foothold. Lacewings, ladybugs, hovering flies and parasitic wasps will then be able to feast on the aphids. If inorganic insecticides have already been used in neighboring yards, the predatory insect population may need to be supplemented. Ladybugs can be purchased at many nurseries or online, and releasing a flock of ladybugs near an affected rose can be satisfying. Some hummingbirds also prey on aphids, and they can be encouraged to visit the shrubs by placing a hummingbird feeder or a bouquet of hummingbird-attracting flowers near the affected roses.
Control with Water
Because aphids are poor climbers, often the best remedy is simply a strong blast from the hose, every three days, until the problem is under control. The soft-bodied aphids will quickly be knocked off the plant and easily drown or become prey for other insects. Aphids often hide on the underside of leaves and other protected areas, so spray thoroughly. Be careful to avoid spraying if black spot or other fungal diseases are present, as water will exacerbate the disease. Watering in the morning will also allow the bush to dry before nightfall. Wet leaves encourage many diseases and should be avoided.
Control with Spray
Citrus sprays can be easily made from lemon or sour orange rind, according to Barbara Pleasant's book, "Gardening Essentials." Grate the rind from two lemons or two sour oranges, mix with one quart of water and let the mixture soak overnight. Strain the rind from the liquid and mix the liquid half-and-half with fresh water before spraying on affected plants. A drop or two of dish washing soap can be added as an emulsifier to prevent the spray from beading or running off the leaves.
Other Prevention Techniques
Dormant oil may be used to suffocate overwintering aphid eggs, but will harm beneficial insect eggs as well. Insecticidal soap or neem spray has the same issue. These methods are not selective and will indiscriminately kill both harmful and beneficial insects. However, for severe infestations, repeated applications of these sprays may be necessary.