Aphids are small soft bodied insects, which pierce plant parts and draw sugars out of the sap stream leaving behind a sticky excretion which is colloquially known as “honeydew.” Most healthy plants can usually tolerate a small population of aphids without suffering any serious health problems.
Oleander and Yucca almost never experience a grave decline in health no matter how heavily infested they become with aphids. However, on other plants a thick invasion of aphids will swiftly reduce vigor by robbing the plant of necessary minerals. Furthermore, honeydew can collect on plant surfaces in the form of a thick shiny coating that often provides a food source for the development of dark molds on leaf surfaces. This sooty mold prevents the penetration of sunlight to the foliage and reduces photosynthesis further impacting the fitness of your plant.
Aphids can also act as vectors for the introduction of viruses in plants. Zucchini and cucumber mosaic viruses are examples of diseases spread by aphids. Aphids are also accused of causing the most common pumpkin virus infections. Infected aphids are not themselves made sick by these viruses but easily spread them to the plants they feed from. A heavy infestation of aphids is not necessary for the introduction of these diseases into your garden. Infected aphids inoculate plants with viruses they harbor when they penetrate plant cells with their sharp mouth parts. Once infected by a virus, little can be done to stem its spread through a plant.
Aphids usually overwinter in eggs, hatching early in spring. Most of these aphids will be females which are born virtually pregnant and will produce fifty to one hundred live offspring over their one month lifespan. Environmental circumstances may cause some of the females to develop wings and relocate to other plants in the garden. As autumn approaches, some aphids will mature as males. Male and female aphids will mate and the fertilized eggs will be attached to host plants for overwintering.
Aphid control on low growing plants is usually not very difficult. A large number of systemic and contact insecticides are labeled for aphid control. One of the safest ways to control aphids is with a steady stream of soapy water. The stream will blast some of them off the host plant and the soap will penetrate their soft bodies and eradicate most of them.
If the aphids have infested tall trees such as Pecans or red oaks (reported frequently this year), they can be treated with a broad spectrum systemic insecticide easily obtained from local nurseries. These insecticides can be drenched into the soil near the base of the tree and results should be seen in about four to six weeks. Obviously, this is of little value with the first freeze just around the corner. The good news is that if your trees are otherwise healthy, treatment is probably not necessary. If on the other hand, your car is covered in sticky honeydew every morning, you may need to call an arborist to get a handle on the problem.
Plants that are native or adapted to our region usually require little in the way of pest control.