Aphids are small, pear-shaped, soft-bodied insects that feed mostly on the leaves of plants, although some species specialize in feeding on the twigs or trunk of the host plant. Aphids can be distinguished from other insects by the two tubes, called cornicles, which protrude from the back of the Aphid abdomen.
Aphids feed on plants by sucking the juices of the plant. Although a single Aphid may occasionally be found, they usually feed in groups - called colonies. A colony may have winged Aphids, but most of the Aphid colony will probably be wingless insects. Aphids may be any color with the most common colors being black, brown, red, or yellow.
Aphid damage isn’t usually noticed until there is a large population of Aphids on the plant, but their numbers can build rapidly. Aphids can reproduce asexually and the time from hatching to adulthood may be as little as 7 - 10 days under optimum conditions.
Aphid feeding will rarely kill a healthy or mature plant. Control is usually initiated due to the visual effects of foliar damage and to prevent the production of honeydew and sooty mold that is associated with Aphid feeding. More significant damage can be done to young plants that have less foliage. In some circumstances Aphids have been identified as transmitting viruses between landscape plants or vegetables.
HOW TO CONTROL APHIDS
Aphids can easily be controlled with environmentally friendly pesticides such as horticultural oils or horticultural soaps. These products will cause minimal damage to beneficial insect populations. Most traditional sprayable insecticides are also labeled for Aphid control, but will kill a larger number of beneficial insects or Aphid predators. Some soil-applied insecticides, such as imidacloprid, are also labeled for Aphids and has the side benefit of not affecting beneficial or predator insects.
If the Aphid population is only found on a few plant leaves the infested leaves could be pruned from the plant and disposed of. A strong spray of water can also be used to dislodge the Aphids from the plant. Most of the displaced Aphids will not be able to make their way back to the foliage of the plant.
Make sure plants are not under stress by supplying sufficient irrigation and fertilization. Over fertilizing, however, should be avoided. Too much nitrogen fertilizer can stimulate succulent growth which would be favorable to Aphid development.
There are several predator insects that attack and feed on Aphids. Ladybird beetles, lacewing insects, and parasitic aphid wasps are common Aphid enemies. Purchasing and releasing ladybird beetles may provide some Aphid control, but because they may fly from your yard, there is no guarantee of success with this method.
Ants commonly tend, or “farm”, Aphids. They do this so they can collect the honeydew the Aphids produce and use it as a food source. In doing so, the ants also protect the Aphids from predator insects. By inhibiting the ants from reaching the Aphids predator insects can significantly reduce an Aphid population. A product called Tanglefoot can be used to stop ants from reaching the Aphids. This sticky product is placed around the trunk of the plant and catches or stops the ants from reaching the Aphids. Tanglefoot should not be applied directly to the tree trunk. Wrap the tree trunk with tape or some other non-porous material and apply the Tanglefoot to the wrap.
TREES AND SHRUBS ATTACKED BY APHIDS
Most plants, whether they are ornamental trees or shrubs, flowers, or vegetables, has one or more species of Aphid that have been known to feed on it.
SIGNS & SYMPTOMS OF APHID DAMAGE
A high level of Aphid feeding will cause leaves to become distorted, curled, or to turn yellow. Inspecting the underside of the leaf will often reveal an Aphid colony on the leaves.
Aphids also release a sugary liquid called honeydew. The honeydew can be seen glistening on the lower foliage of the plant or on anything that is under the infested plant. Sometimes a black fungus called sooty mold will grow on the honeydew. Although sooty mold doesn’t infect plant leaves it can block sunlight from reaching the leaves, which then inhibits photosynthesis from occurring.
A strong spray of water and a mild soap can be used to remove sooty mold from plants or anything else the sooty mold is growing on. Some plants may be harmed by soap, so before using any kind of soap on a plant test a small area of the plant with the solution first. Spray the mixture on a few leaves and wait 5 - 7 days to see if any adverse reaction occurs.
Aphid excreting honeydew. Photo: Sanjay Acharya.
Adult aphid with nymph aphids. Photo: Shipher Wu.
Adult & nymph aphids. Photo: Michel Vuijlsteke
Adult ladybird beetle eating an aphid.
Ladybird beetle eating an aphid. Photo: Sanjay Acharya