Ministry of Environment
Integrated Pest Management
Most gardeners are familiar with aphids—the tiny, numerous pear-shaped insects that suck plant sap. They are common pests on roses, vegetables, fruit and shade trees, and ornamental shrubs. Aphids suck plant sap, which distorts leaves and new growth and may weaken the plant. Some spread plant viruses and most aphids secrete honeydew as they feed, which leaves a sticky coating on leaves and fruit (or your car!) below. Unsightly, but harmless, sooty moulds often grow on the honeydew.
It is important to realize that aphids are not always a problem. Some plants are damaged very little by aphid attacks and aphids feeding on shrubs and trees in late summer can help harden off new growth before winter.
In the spring, overwintered aphid eggs hatch into females. These do not mate, but they are able to give birth to live nymphs continuously (up to 10 or more per day) during the growing season. In the fall, these "stem-mothers" produce male and female aphids that mate and produce eggs that overwinter. When they become too crowded some aphids grow wings and migrate to new plants.
Aphids are difficult to control using sprays because any survivors quickly develop new colonies. Aphid populations also become resistant to insecticides used repeatedly.
The best long-term control for aphids is provided by their natural enemies. An aphid infestation that is ignored by the gardener almost always disappears thanks to the action of hundreds of native species of predatory bugs, beetles, flies, lacewings, midges and numerous tiny parasitic insects. You can attract this army of native beneficial insects to the garden by planting flowers and herbs among the vegetables; protect them by not using insecticides.
If you want to speed the disappearance of an aphid infestation:
- Wash aphids off plants with a strong stream of water, repeat in 3 - 4 days and again, weekly, if necessary. This is remarkably effective and will suffice for most infestations.
- To kill overwintering aphid eggs, spray dormant oil on fruit trees in February.
- Early in the spring, release aphid midges (Aphidoletes aphidimyza) to boost the beneficial population. This is a native species sold commercially in B.C. One release of 250 midges is usually enough for the average yard or small orchard. Watch for the tiny, bright orange midge larvae among the aphids.
- Spray commercial insecticidal soap or make a soap spray of 10-25 ml liquid, non-detergent soap to 4 litres of water (1-2 tablespoons per gallon). Test spray homemade mixtures on a few leaves first and wait for a day or two to make sure the mixture does not burn leaves. Repeated applications of soap sprays damage tender foliage, therefore avoid using soaps on the same foliage more than 3 times in a row.
Home-made mixtures of hot peppers, onions and garlic work for some gardeners. Liquefy the ingredients in a blender, mix with sufficient water to make a spray, strain through fine mesh and add a small amount of non-detergent soap (1-2 ml per litre).
As a last resort, spray with domestic garden products containing pyrethrins, which are extracted from pyrethrum daisies, or rotenone (use wettable powder formulations). Although these botanical insecticides break down quickly in the environment, they are as toxic at the time of application as other, more persistent chemicals. Always wear protective clothing, rubber gloves and a tight-fitting dust mask to spray pyrethrins or rotenone and follow directions on the label. Never use these insecticides near ponds or waterways because they will poison fish.