Aphids, often called plant lice, are small, soft-bodied insects that suck juice from plants. Aphids are typically teardrop-shaped and may be winged or wingless. Their long, slender mouthparts are used to pierce plant tissue to suck plant sap.
They range in size from a 10th of an inch to almost invisible to the naked eye, with one exception - the giant bark aphid, which may reach a quarter-inch or larger. They come in all the colors of a rainbow plus brown and black, allowing them to be somewhat disguised on their host plant. They are members of the insect family Homoptera.
Worldwide, there are 32,000 different species, so no wonder you are likely to encounter these little pests. They feed on plant juices from stems, leaves and flowers and can be found on nearly every species of wild and cultivated plant.
Most species of aphids found in the Southwest overwinter as eggs. The eggs hatch with warming temperatures in early spring. The newly hatched aphids begin to feed, and complete their development in one to two weeks. These aphids give birth to live young, without mating, at the rate of one to 20 per day. The number of aphids born depends upon the species, environmental conditions, food availability and the presence of natural enemies.
Aphid's usually develop and feed in colonies. Unlike other insects that feed on plants, they do not disperse when disturbed. Aphid populations normally consist entirely of females, which continue to produce live young, or nymphs, without mating throughout the summer. As they grow, they molt and shed their skins approximately four times before they become adults. This may take only two or three weeks during warm conditions. The first generation is wingless, but as the population increases and becomes crowded, winged aphids develop. Most of theses winged individuals leave the colony in search of a new host plant. When temperatures begin to drop in the fall, both male and female aphids are produced. These aphids mate and the females deposit eggs on plants where the eggs overwinter.
Aphids tend to congregate on leaves and shoots, particularly at the tips of new shoots. They prefer the underside of leaves on succulent new growth for feeding and protection from the sun and drying conditions. Young, swelling leaves and flower buds are a favorite target, which is why young seedlings may be severely damaged or killed by aphids. When abundant, aphids can cause serious damage to larger plants. Some species of aphids have "saliva" that, when injected into plant cells during feeding, causes abnormal, often twisted plant growth. This can be the first obvious sign of a heavy aphid infestation.
Heavy feeding usually stunts growth, deforms leaves, flowers or fruit, or forms galls on leaves, stems or roots. Leaf distortion from heavy feeding by aphids is commonly seen on leafy vegetables, honeysuckle, plum, cherry and ash trees.
Aphids may transmit plant diseases, such as viruses, from plant to plant as they feed. These viruses cause yellow, mottled or curled leaves and stunted growth. Root-feeding aphids also slow growth.
While feeding, they excrete a sweet sap-like liquid called "honeydew" that attracts ants and other insects. Some ants and wasps "herd" and "milk" aphids, using the liquid as a source of food. To safeguard their source of honeydew, these insects will protect aphids from natural enemies. Often a line of ants ascending a tree trunk is our first indication of aphids being present.
In order to control an aphid population, the ants protecting the aphids may need to be controlled first, and then natural predators may be able to reduce the aphid population and eliminate any additional control measures. Not only does this honeydew create a sticky mess, it often supports the growth of sooty mold that gives landscape plants, fruits and vegetables a dull, dark cast and makes them undesirable. Honeydew and molds can usually be washed off plants and fruits; these are then safe for eating. However, on leafy vegetables and crops such as broccoli, cabbage, cauliflower and Brussels sprouts, honeydew, mold and aphids are more difficult to wash off.
Early detection is the key to preventing aphid infestation. The flight of the winged colonizers cannot be predicted, so a weekly inspection of your plants will help early detection. Buds and new growth are key locations. If only a few are found, they can be removed with your fingers - or remove the entire leaf, put it into a sealed bag and discard. In many cases, a strong burst of water will dislodge them, but repeating the process for two or more days may be necessary.
It is highly advisable to remove excess debris, weeds and any plant material susceptible to aphid colonization from your location, and always inspect all vegetable and ornamental plants before bringing them home.
Natural enemies play an important role in aphid control. Ladybeetles, lacewings, Syrphid fly larvae, small parasitic or predaceous wasps are all natural predators of aphids. Plant flowers that produce nectar in your garden or yard to attract these natural enemies. It is necessary to control ants tending aphids in order for natural enemies to migrate in and control the aphids. Ants in trees and single-stemmed shrubs can be prevented from reaching the aphids by the use of sticky barriers applied around the trunks and branches, or try using baits to eliminate the ants at their source.
If aphids colonies are found on 5 percent or more of the foliage, then control measures should be considered. Most products used for aphid control work as contact insecticide. In other words, the aphids must be hit directly with the spray so it can be absorbed by the insects' bodies. Since aphids tend to dwell on lower leaves, this can be difficult sometimes. There are a multitude of pesticides and insecticides that list aphid control. Always read the label and follow manufactures instructions, apply to target area only and avoid over-spraying.
Never use a systemic insecticide on fruit trees or vegetables. Systemic insecticides are absorbed into the roots and foliage of plants. Horticultural oils, insecticidal soaps and other organic solutions are also effective.
Both Organic Gardening and Farmers Almanac list several homemade sprays for control of aphids. No matter what method you choose, never apply any liquid to plant foliage when the ambient temperature is over 80 degrees.
Although aphids seldom kill a mature plant, the damage they do and the unsightly honeydew they generate warrants control.
Happy gardening, hopefully you can enjoy your summer with out aphids.