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Non-Chemical Control of Plant Pests: Aphids

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Non-Chemical Control of Plant Pests: Aphids
Photography by Luc Viatour

At only one to six millimeters long, the soft-bodied, pear-shaped aphid is a tiny, difficult-to-see plant pest. Some aphids have wings, while others don't, but all have two long antennae and six long legs. Different aphid species are different colors and can also be impacted by the plants on which they feed; thus aphids may be green, yellow, brown, red or black. However because the biology, habits and damage of all these species are similar, so too are the recommendations for their management.

Aphids may be found singly or in groups, and they are usually wingless. However, when populations grow large, winged aphids will often be present as well, enabling it to disperse and form colonies in new areas. Aphids can be distinguished from other similar plant pests, such as mites or thrips, by the fact that they will not move off rapidly when disturbed.

Aphids can reproduce asexually and can develop into reproductive adults in about a week. During this same week, the adult aphids can have produced up to 80 offspring.

Plant hosts: Aphids will feed on virtually any indoor, garden or ornamental plant. They primarily colonize new growth, but will also feed on other parts of the plant, including leaves, stems, bulbs and roots.

Damage: The aphids feed on plants for their sap. Although one or two aphids that are quickly eliminated may cause little to no damage, high and quickly developing populations can cause significant damage: Their feeding causes leaves to curl and yellow, and shoots to become stunted. This insect also secretes honeydew which coats the plant and attracts secondary pests such as ants. Some species also inject a toxin into the plant further damaging it. In addition, the aphids can transmit viruses to vegetable and ornamental plants.

Signs: The curling leaves are distinct signs of aphid activity. It is particularly critical that these leaves be clipped, as aphids can hide beneath the curling leaves and make it virtually impossible to see or eliminate them. Clipping and examining undamaged leaves can also be a good way to check for aphids. High populations of ants on and around plants can also be a sign that aphids may be present, as the ants feed on the honeydew the aphids produce.

Non-Chemical Control

  • Wash entire plant with soapy water (approx. 2 tsp mild detergent per gallon of water).
  • Plants that can withstand high water pressure can be hosed with a forceful spray to knock off the aphids and their honeydew. Pay particular attention to the underside of the leaves. This can be done as often as can be withstood by the plant.
  • Prevent aphids from entering homes or greenhouses by ensuring that all door and window screens are in good repair. Screening vents can also be helpful to prevent entry by these – and other pests.
  • Prune any parts of a plant that are heavily infested.
  • Because they have very soft bodies, small numbers of aphids can be eliminated by squishing them with fingers.
  • Inspect new plants to ensure they are aphid-free before placing them with established plants. It can be helpful to quarantine them first to ensure no less-visible eggs were brought in with the plant.
  • If planting outdoors, check the area and plants in the vicinity for signs of aphids.
  • Eliminate these prior to planting.
  • If ants are seen climbing the plants to tend the aphids, try placing a band of Teflon or sticky material around the plant to keep the ants from climbing, or otherwise controlling and eliminating the ants from the area.
  • Aphids are attracted to and can easily cause significant damage to seedlings, so growing these under protective covers can help keep aphids away during this important growth time.
  • The aphid's natural enemies are the green lacewing, the fall midge and some species of ladybugs.

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