Common Garden Pests: Aphids

February 22, 2017

The aphid is one of the most common garden pests. Worldwide there are over 4,000 species of aphids, feeding on numerous garden plants, from annuals and perennials to flowering shrubs. Not every plant is susceptible to aphids. Usually, each species has only a few plants, or sometimes only one plant, on its menu. Common host plants in Northwestern Ontario gardens include fuchsias, vinca vines, asparagus ferns, carnations, chrysanthemums, English daisies, tomato plants and rose bushes.

Aphids spend the winter as eggs. In spring, the newly hatched aphids are all female. They multiply rapidly, continuously giving birth to as many as 10 live nymphs per day. Several generations occur in one summer. When temperatures become cooler in autumn, some males are produced. The males and females mate to produce eggs, which go on to overwinter on plants and trees, then hatch as new females in spring.

Aphids are tiny and slow moving. Their bodies are soft and pear-shaped. In our area, they are usually pale green or whitish, but species in other parts of the world can be brown, black, pink or red. They will be found in clusters on stems or on the underside of leaves. They are especially fond of tender, succulent new growth. If you suspect an aphid infestation the first place to look is on the plant's newest leaves.

Aphids cause damage when they suck substantial amounts of a plant's juices, weakening it and leaving it open to diseases. Symptoms of an infestation include discolouring, wilting, curled leaves and deformity of leaves, especially new growth. Leaves may also be coated with a shiny, sticky film. This substance, called honeydew, is excreted by aphids when they cannot metabolize all the sugar they suck from the plants. Ants are fond of honeydew and have been known to purposely carry aphids onto plants in anticipation of a sweet reward.

Thankfully, aphids are quite easy to control. Some people swear that certain plants repel aphids and using these next to susceptible plants will protect them. Try planting garlic, chives, anise, coriander and petunias in your garden if you want to test this theory. For light infestations you can try squishing the aphids or spraying them off with water. A natural, organic insecticidal soap is also effective, although more than one application is often required.

Insects are natural visitors to your garden. While some, like aphids, are harmful, others are beneficial, such as ladybugs and their larvae, which eat aphids, as many as 2400 in their lifetime. If you are lucky enough to have ladybug friends in your garden try to protect them as well as they protect your plants from serious predators like aphids.