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Ministry of Agriculture, Food and Rural Affairs

Aphids

Aphid colony on leaf Aphid adults and young nymphs Aphid damage Click to enlarge.

Beginner

Scientific Names
Myzus persicae, Brevicoryne brassicae, Lypaphis erysimi

Identification

  • Small, pear-shaped insects, with cornicles or “tail-pipes” near the tip of their abdomen
  • Typically found in colonies located on the underside of the leaf, or along the stem or petioles
  • Aphids pierce the leaves and suck the sap from many vegetable crops, causing leaf distortion
  • Aphids act as a primary vector of several economically significant virus disease, spreading the virus as they feed

Often Confused With
Leafhoppers
Tarnished plant bugs

Period of Activity
Aphids are present throughout most of the growing season. Populations build quickly during hot, dry weather. Aphid populations are often kept below threshold levels where predators (ladybird beetles, lacewings, minute pirate bugs, etc.) are present in abundance.

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field. Watch for the presence of aphids on the developing fruit. Take note of any aphid populations that continue to build over a several week period. Inspect the underside of leaves from the top, middle and bottom of plants.

Thresholds
None established. Treat if aphid populations begin to build directly on the fruit.

Advanced

Scientific Names
Myzus persicae
, Brevicoryne brassicae, Lypaphis erysimi

Identification
Aphids are small, pear-shaped insects, with cornicles or “tail-pipes” near the tip of their abdomen. They are typically found in colonies located on the underside of the leaf, or along the stem or petioles. Aphids pierce the leaves and suck the sap from many vegetable crops. Their feeding causes leaf distortion.  Aphids produce a sticky substance called “honeydew,” which can promote the development of secondary moulds (sooty mould). These moulds may affect marketability.

Often Confused With
Leafhoppers
Tarnished plant bugs

Biology
Aphids also act as a primary vector of several economically significant virus diseases. Non-colonizing aphids move through the crop in search of suitable host plants, spreading the virus as they feed. With many viruses, the disease infection occurs after less than 1 minute of feeding. The control of aphid populations with insecticides does little to prevent the spread of viruses.

Period of Activity
Aphids are present throughout most of the growing season. Populations build quickly during hot, dry weather. Aphid populations are often kept below threshold levels where predators (ladybird beetles, lacewings, minute pirate bugs, etc.) are present in abundance.

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field.  Watch for the presence of aphids on the developing fruit.  Take note of any aphid populations that continue to build over a several week period.

Thresholds
None established.  An otherwise healthy crop can tolerate fairly high numbers of aphids without suffering yield loss.  Treat if aphid populations begin to build directly on the fruit.

Management Notes

  • After harvest, crop residues that are heavily infested with aphids should be worked into the soil. This will prevent aphids from moving into later plantings and will also reduce the numbers of cabbage and turnip aphids surviving through the winter.
  • Transplants should be examined for aphids and treated before placing in the field. Even relatively small numbers of aphids can increase rapidly and damage transplants.
  • There are numerous species of predatory and parasitic insects which serve to regulate aphid populations. Important predators include the ladybird beetles, minute pirate bugs, lacewing larvae, syrphids, predatory midges, ground beetles and spiders.
  • Aphid numbers often increase dramatically after the application of insecticides which are detrimental to beneficial insects. Broad-spectrum materials such as pyrethroids should be used only as required in an IPM program where aphid control is a consideration.
  • Later in the season, large number of aphids frequently become infected with fungal diseases. Outbreaks of disease are favoured by dense plant canopies, large aphid populations, and moist conditions. Periods of heavy rain can directly dislodge aphids from plants and promote the development of these diseases.