On first appearances this insect may be confused with cabbage whitefly. However, mealy cabbage aphid does not fly up in a white cloud when disturbed. Other symptoms to look out for include:

• Dense colonies of greyish-white aphids, up to 2.5 mm long, clustered on the underside of leaves and on the growing points
• The leaves develop a whitish-yellow discolouration where the aphids are feeding
• On young plants, the foliage develops in a distorted manner and the growing point may be killed
• In addition to edible and ornamental brassicas, this aphid can also be found on some related wild plants, such as charlock and shepherd’s purse
• On most brassicas these insects can be tolerated and are a food source for many aphid predators, which can wipe out aphid colonies. On kale and young plants palatability and growth can however be affected

• Where possible tolerate populations of aphids
• Check brassicas frequently from spring onwards so action can be taken before a damaging population has developed, especially on more vulnerable young plants and kale
• Use finger and thumb to squash aphid colonies where practical
• Encourage aphid predators in the garden, such as ladybirds, ground beetles, hoverflies, parasitoid wasps and earwigs. Be aware that in spring aphid populations often build up before natural enemies are active in sufficient numbers and then give good control
• Dispose of old brassica plants once they have finished cropping to reduce the risk of the next season’s plants becoming affected

Mealy cabbage aphid overwinters on its host plants as eggs that are laid on stems in late autumn, although in mild winters aphids can be active throughout winter.

For most of spring and summer, the aphids are present as wingless females that give birth to live young.

Winged forms develop when plants have very large populations, allowing the aphids to migrate to new host plants.