• Topics: Landscape Pests | Ornamentals (MG Entomology) | Landscape Aphid Pests | Buss, Eileen A

Aphids on Landscape Plants ¹

Aphids or "plant lice" may infest almost any plant. They are more commonly found on camellia, crape-myrtle, gardenia, hibiscus, ixora, oak, oleander, ornamental grasses, palm, rose, as well as nearly all annual plants. Aphids have piercing-sucking mouthparts and cause damage by sucking the plant juices. However, their ability to transmit plant viruses may be more harmful than any direct feeding damage.

Aphids (Figure 1) are soft bodied pear-shaped insects generally less than 1/8 inch long. They may be green, black, brown, pink, yellow, blue or creamy-white in color. Most aphids are wingless but when colonies become overcrowded or the host plant becomes undesirable, winged forms are produced which establish new colonies. Aphids have two short cornicles or tubes at the end of their bodies, or spots to indicate where the corricles should be. These insects are commonly found on the stems or undersides of young leaves in small colonies.

Figure 1. 

Rusty plum aphid.

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Most aphids feed on the new plant growth. Their feeding makes the leaves curl or crinkle (Figure 2) and flower buds may become hardened, causing the flowers to be distorted.

Figure 2. 

Black citrus aphid on camelia.

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Aphids have complex life cycles, and some species may alternate generations on different hosts (e.g., a tree and then a grass species). These pests are unlike many other insects in two ways: almost all are females that reproduce without mating, and most give birth to living young instead of laying eggs. Aphids have the ability to reproduce rapidly and there are many generations per year. Each female aphid produces 50 to 100 daughters during her life span and each daughter can reproduce within 6 to 8 days.

Aphids as well as soft scales, mealybugs, and whiteflies excrete large amounts of honeydew which provides an excellent medium for the growth of a black fungus called "sooty mold." Besides being unattractive, sooty mold may interfere with photosynthesis and retard plant growth. Sooty mold usually weathers away following control of an insect infestation. Ants feed on the honeydew and when ants are observed, plants should be examined closely for these sucking pests.

Beneficial Insects

Some examples of aphid predators are lady beetles (adults and larvae), hover fly larvae, assassin bugs, ambush bugs and spiders. Aphids that have a small hole in a bloated-looking body (Figure 3) have been parasitized by tiny wasps. If predators are present or the pests show signs of parasitism, every effort should be made to preserve the beneficial insects. Delay applying a pesticide until damage appears, and provide the beneficials an opportunity to control the pest populations.

Figure 3. 

Healthy (yellow) and parasitized (brown/swollen) oleander aphids.

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Inspecting Plants

Examine your plants weekly during the spring, summer, and fall. Look at the undersides of a few leaves on each plant and observe the stems for aphids, especially the new growth. The use of a 10 to 15 power hand lens or magnifying glass aids in detection and identification. Learn to determine when aphids are present in damaging numbers and to evaluate the potential of the predator or parasite population. To aid in locating aphids, a sheet of white paper or cloth may be held beneath the leaves and the foliage struck sharply. The insects will fall onto the paper and can be more easily observed and identified than on the green foliage.

Non-Insecticidal Control

Many homeowners can remove aphids and keep populations below damaging levels by spraying their landscape plants with a forceful stream of water. Use a garden hose with an adjustable nozzle and spray undersides of leaves and stems when the aphids appear.

Soaps are available that are formulated for controlling insects and related pests. If one of the commercial soaps is unavailable, 3 tablespoons of dishwashing liquid (do not use those containing a degreaser or an automatic dishwashing soap or detergent) per gallon of water may be applied as a foliar spray to woody plants. Use 2 tablespoons for bedding, foliage and flowering plants. Repeat at weekly intervals as needed. Soap is effective in controlling aphids, safe for people and the environment.

Many homeowners can remove aphids and keep populations below damaging levels by spraying their landscape plants with a forceful stream of water. Use a garden hose with an adjustable nozzle and spray undersides of leaves and stems when the aphids appear.

Soaps are available that are formulated for controlling insects and related pests. If one of the commercial soaps is unavailable, 3 tablespoons of dishwashing liquid (do not use those containing a degreaser or an automatic dishwashing soap or detergent) per gallon of water may be applied as a foliar spray to woody plants. Use 2 tablespoons for bedding, foliage and flowering plants. Repeat at weekly intervals as needed. Soap is effective in controlling aphids, safe for people and the environment.

Insecticidal Control

Usually aphids are not difficult to control with insecticides. But, plants may become re-infested from adjacent areas throughout the year. For control, apply one of the suggested insecticides (see Table 1) if aphids are beginning to damage the plants. Spray the plants to the point of run-off. Be especially careful to cover the undersides of the leaves and all parts of the twigs thoroughly. Continue to inspect the plants periodically especially new flushes of growth and apply an insecticide if plants become re-infested.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, Dean.

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