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Description:

Aphids are small (about 3 but up to 5 mm), soft-bodied, somewhat pear-shaped insects that have long, thin antennae, six legs and may be green (most species), yellow, red, pinkish, purple-brown or black. Most aphids in a particular population are wingless and they usually have a pair of tube like structures that stick out from their abdomen called cornicles. These insects have piercing-sucking mouthparts. There are many species of aphids in the Order of Homoptera (e.g. Norway Apple Aphids (Periphyllus lyropictus), Woolly Apple Aphids (Eriosoma lanigerum).

Symptoms of Aphid Infestation:

Aphids are often found in clusters. They cause damage by sucking the sap from the underside of young stems and growing tips. Aphid damage can also be seen on leaves (including yellowing, curling, puckering, twisting and general deformation). Another likely indicator is a sticky honeydew liquid on the plants, which is actually the body waste of many species. Sometimes a secondary fungus, called black sooty mold, will grow on the honeydew, making the affected plants look unsightly.

Plants Affected:

A wide variety of ornamentals, shrubs and trees can be affected including asters, browallia, calendula, cosmos, dahlias, gladiolas, hollyhocks, iris, petunias, primula, roses, shepherd's purse, sunflowers, sweet pea, zinnia, spireas, flowering cherry, snowball viburnum, birch, linden, willow and Norway maple. All vegetables are susceptible but aphids are most commonly found on a wide variety of vegetables including green bean, broccoli, brussel sprouts, cabbage, cauliflower, cucumber, lettuce, peppers, potato, melon, sweet corn and rutabaga. Fruits such as apple or cherry can also be affected.

Life Cycle and Habits:

Female aphids can reproduce sexually or asexually. In the springtime and throughout the growing season, females, reproducing asexually, give birth to five live, female young. Sexual reproduction occurs in the autumn or under conditions of extreme overcrowding. Aphids possess the capability to develop wings during conditions of overcrowding, enabling them to fly to another host plant or search for a male. Eggs either hatch shortly after being laid, or remain over winter and hatch in the spring. Nymphs are able to reproduce in ten to twelve days after hatching.

Ants often carry aphids around on their backs and therefore are often responsible for spreading aphids. Sometimes control of aphids is dependent upon control of ants.

Organic Management/Control Strategies:

The City of Toronto adopted a new municipal by-law (spring 2004) that restricts the use of pesticides. For details about the by-law visit the Pesticide by-law page on Toronto Public Health's Web site at www.city.toronto.on.ca/pesticides or www.toronto.ca/health. Questions may be e-mailed to pesticide@toronto.ca. Aphids are rather weak in physical strength and speed, and can be controlled using a number of organic interventions.

Natural Control:

• Predatory insects such as ladybugs and lacewings can be released in the garden to feed on aphids. They can be purchased at some garden centres, usually in late spring.

Mechanical Control:

• Aphids can be easily knocked off a plant with a strong jet of water from a hose. (Spray both upper and lower leaf surfaces).
• Potato and rose aphids lay their eggs on the tips of roses. Control by tip pruning the roses or, to smother eggs, apply dormant oil in the springtime before bud break.
• Insecticidal soap or liquid hand soap mixed with water can be sprayed on aphids.
• Silicon dioxide (diatomaceous earth), dusted on affected plants, is also effective.

Cautions/Considerations:

Aphids can be very difficult to control once they become established and leaves curled (e.g. fruit trees).

References:

The Toronto Botanical Garden Weston Family Library is an excellent source for horticultural information.

• Yepson, Roger B.Jr. ed. The Encyclopedia Of Natural Insect and Disease Control. Pennsylvania, U.S.A.: Rodale Press, 1984.

• Cranshaw, Whitney. The Ultimate Guide to Backyard Bugs. Princeton, U.S.A.: Princeton University Press, 2004.

• Alford, David V. A Colour Atlas of Pests of Ornamental Trees, Shrubs and Flowers. Portland, Oregon: Timber Press, 2003.

• The Gardener's Handbook - An Integrated Approach to Insect and Disease Control, Toronto, Canada: Publication 64. Ontario Ministry of Agriculture, Food and Rural Affairs, Queen's Printer for Ontario, 1998.

Factsheets are produced by the Toronto Master Gardeners in association with the Toronto Botanical Garden. They provide introductory information about a broad range of horticultural topics and are intended for personal use and study purposes. Should your gardening group or organization wish to use multiple copies we ask that you inform the Toronto Botanical Garden at info@torontobotanicalgarden.ca.

Date revised: January 8, 2006