Biology and management of the mealy cabbage aphid
Mealy cabbage aphid is a serious pest of vegetable brassicas as infestations can lead to distorted foliage, contamination of produce by aphids, wax, cast skins and honeydew, yield loss and even plant death. It is also an important vector of several viruses, including Turnip mosaic virus (TuMV) and Cauliflower mosaic virus (CaMV).
Risk factors in oilseeds and vegetable brassicas
- Spring oilseed rape is at highest risk, although mild winters can result in damaging infestations on winter oilseed rape
- Hot, dry summers can result in large populations
Scientific name: Brevicoryne brassicae
Wingless aphids are up to 2.6 mm long, green and covered with a greyish-white mealy wax, with short, transverse, dark bars on the upper side of the thorax and abdomen.
Winged aphids have a dark head and thorax.
Mealy cabbage aphid life cycle and crop damage
Nov–Feb: This species overwinters on brassica crops and wild hosts, mostly in their active stages, although some may overwinter as eggs.
Mar–Oct: The production of winged forms allows this species to move to new brassica crops, multiplying rapidly in hot, dry conditions.
Initial symptoms in vegetable brassicas are small, bleached areas on the leaves that become yellowish and crumpled. Young plants can become stunted and die, especially in unfavourable weather.
Early infestations in oilseed rape occur under leaves, but later infestations move to developing flowers and pods and can result in dense colonies. Autumn feeding often causes leaf distortions, twisting of the midrib and chlorotic patches. The crop usually recovers in the spring. In spring oilseed rape, serious infestations can cause pod distortions and yield loss.
On all crops, Turnip mosaic virus (TuMV) and Cauliflower mosaic virus (CaMV) cause leaf mottling and vein clearing, stunting, and black mottling and streaking on stems.
Non-chemical and chemical control
Natural enemies include parasitic wasps (for example, Diaeretiella rapae), ladybirds, hoverflies, lacewings, several predatory flies, spiders, and insect-pathogenic fungi. Providing habitats that encourage the presence of these natural enemies may help control aphid numbers.
However, they may not prevent virus transmission because this can occur even at low aphid densities.
Biopesticides are being evaluated for control of this pest.
- Winter oilseed rape: >13% of plants infested before petal fall
- Spring oilseed rape: >4% of plants infested before petal fall
- Vegetable brassicas: none established