Aphids on Ornamentals

Ornamentals Advisory Blog

Aphids are serious pests in ornamental plants, causing both direct and indirect damages through loss of saps, deformation, discoloration, abnormal development, reduced photosynthesis because of sooty mold growth, and transmission of plant viruses which may have severe economic impacts. The control strategies against aphids infesting ornamental plants typically involve of synthetic insecticides.

Aphids are economically important pests on many ornamental crops. Under the optimal environmental conditions of the greenhouse, parthenogenetic (asexual) and viviparous (live-bearing) reproduction can continue year-round. In such circumstances, large populations are quick to develop.

Aphids damage crops directly, wilting and distorting leaves and flowers as they feed, but they also cause a number of other problems. The physical presence of a large number of aphids can be a cause for concern, and the honeydew they excrete as they feed promotes the growth of black sooty molds, which in turn reduce the crop's photosynthesis as well as its aesthetic value. Dust, dirt, and skins shed in molting adhere to the viscous substance, making plants unsightly. Furthermore, aphids transmit several plant viruses.

Because many ornamental crops have little tolerance for damage, growers need to identify aphid populations early and take appropriate control measures. The need for early control has resulted in the sometimes-unnecessary prophylactic use of chemicals for aphid control in greenhouses and nurseries.

Symptoms

Aphids usually prefer to feed on succulent young shoots and leaves, although some species occur on flowers, twigs, branches, or even roots. They seldom kill plants, but their feeding can cause stunted plant growth, curled and yellowed leaves, or distorted stems and fruits; some species cause galls on roots, leaves, or stems. Damage results primarily from the loss of plant juices, although some aphid species transmit plant viruses or inject toxins into plants while feeding. Aphids, and certain other plant sap sucking insects, excrete large amounts of honeydew, a sticky substance often seen on leaves, pavement, automobiles, or other surfaces below infested foliage. Honeydew consists mainly of excess sugar ingested by the insects and passed through the body. Ants are often attracted to the sugary honeydew and occasionally tend the aphids much as man tends cattle; some ants even carry aphids to new plant parts to establish more colonies. Honeydew also attracts flies, wasps, and bees, thus adding a nuisance element for humans. A black sooty mold often grows on plant parts covered with honeydew. This fungus can detract from the plant's appearance and reduce the amount of light reaching leaves (thus reducing photosynthesis).

Life Cycle

 The "typical" aphid species may produce several wingless generations in the spring, followed by a generation of winged forms. The winged forms can fly to other plants where many more wingless generations may be produced. As days become shorter and cooler, a generation of winged aphids may be produced which fly back to the host. Aphids can increase rapidly in an extremely short time. During warm weather some species can complete a generation in less than two weeks. In many species, most or all the generations consist of females which give birth to live female young and are produced without sexual reproduction (parthenogenesis). Males may be produced near the end of the cold season.

Description

Aphids are small (usually 1/8-inch-long or less), delicate, more or less pear-shaped insects with long legs and antennae. Their color can vary from green to brown to red or black. They may be winged or wingless, but wingless forms are more common. Most aphids have a pair of tube-like structures, called cornicles, projecting backwards near the rear of the body. They have piercing-sucking mouthparts and feed by sucking sap from plant tissue.

Management

Non-Chemical control

In some cases, cultural practices such as proper pruning, fertilizing, and watering play an important role in preventing or suppressing an aphid infestation. When practical, try washing aphids off an affected host with a strong stream of water.

Beneficial insects play an important role in aphid control. Lady beetles (both adults and larvae), lacewings, some flower flies (larvae), and tiny parasitic wasps will use aphids as a source of nourishment for the development of their offspring.

Chemical control

The use of insecticides is often the only effective means of managing an aphid infestation. Several registered insecticide formulations are available for aphid control. However, to avoid damaging valuable plants, apply the material only to plants that are specified on the label. Be sure to follow all insecticide label directions. Chemical control recommendations: Actara, Chess and Karate Zeon.