Identifying and managing aphids

There are many varieties of aphids. Not all aphids are pests in the garden, but those that are wreak havoc when left to their own devices. Follow our guide to controlling aphids without resorting to the use of insecticides.

Aphids are small (up to 1⁄8 inch), soft, rounded insects with little wings. Upon closer inspection, a pair of pipe-like cornicles usually can be seen protruding from the back of their bodies. They come in a wide variety of colors ranging from light yellow to dark, nearly black. They are often referred to by the type of plant they attack, for example Black cherry aphid, Wooly apple aphid, or Pea aphid.

Aphids have the potential to become particularly nasty garden pests. They feed by piercing holes in plant tissue and sucking the juices. This makes them efficient at transmitting disease from one plant to another.

Where are they found?

• Aphids are found throughout North America. They feed on a wide range of fruits and vegetables, flowers, ornamentals, and shade trees.
• Aphids feed in large groups and tend to attack new shoots, tips and bulbs – although some species feed on all parts of a plant including its root system.
• Infestations are at their worst in spring, early summer, and again in autumn.

Identification

• Warning signs of aphid infestation include distorted shoot tips and new leaves. Some aphids cause wilting, leaf curling, and dieback of shoots and buds.
• The presence of a sticky coating (honeydew) is another telltale sign of aphid infestation. Honeydew is often accompanied by a black sooty mold that detracts from a plants appearance.

Damage

• Because aphids feed by sucking sap from plants, they are efficient at transmitting viral diseases from one plant to another.
• Aphids produce a sticky honeydew substance. This is the waste material they excrete after feeding on plant sap.
• Honeydew covers the leaves, stems, and branches of infested plants and turns black when covered with sooty mold. Apart from its generally unattractive appearance, it tends to attract large colonies of ants.

Breeding

• Most aphids are female. It is usual for a female to give live birth to a genetically identical daughter through asexual reproduction (referred to as parthenogenesis).
• Aphids breed prolifically. Adults produce three to six young per day over the course of their lifetime, which usually extends to about a month.
• As a consequence, populations can increase dramatically resulting in infestation within only a matter of days.

Controlling aphids

Introduce only healthy plants

• Aphids are commonly introduced into a garden on new planting material.
• Always obtain your plants from a reputable organic supplier.
• Before purchasing plants in the form of transplant sized individuals, crowns, rootstock or young trees or shrubs visually inspect all foliage for the presence of aphids.

Routinely inspect plants

• Routinely inspect garden plants for the telltale signs of aphid infestation (wilting, leaf curling, dieback of shoots and buds, and the presence of black sooty mold).
• Early identification of potential problems allows a range of interventions to be applied before aphid populations get out of hand. This greatly reduces the need to rely upon commercially prepared insecticides.

Encourage natural predators

• Prevent aphid infestations by encouraging natural biological systems.
• Aphids are basically defenceless and are a food source for a wide range of natural predators and parasites. Lady beetles, lacewing larvae, aphid midges, and parasitic wasps are all effective at helping to control aphid populations.

Physically remove aphids

• Physically remove aphid populations by rubbing affected plant stems and branches with a moist cloth.
• For aphid populations located on more delicate plant areas, use jets of water. Use a misting bottle, and adjust the nozzle to a single stream. Squirt water at populations to dislodge and lethally injure aphids. Any aphids that do survive will be unlikely to make their way back to the host plant.
• Light scale infestations can simply be removed with your thumbnail.

Manage weeds effectively

• Many weed varieties host aphids. Effectively managing weeds and their numbers is an effective means of controlling aphid numbers.
• Understand which weed varieties in your garden host aphids and routinely remove these weed types.

Apply hot pepper or garlic repellent spray

• When aphid infestation is widespread amongst plant foliage and steps 1 through 5 have proved ineffective, apply a hot pepper or garlic repellent spray.
• An appropriately prepared garlic or hot pepper spray applied once every two to three days for about two weeks should prove effective at killing persistent aphid populations.