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Pests and diseases: Mealy cabbage aphid




  • Look for

    Waxy residues and small white skin sheds on leaves and heads of many brassicas and cabbage family plants. There may be a covering of a sticky, sugary substance on the leaves which could become infected with sooty mould. Leaves may become yellow with high infestations. Dense colonies of aphids may be found on the undersides of older leaves.

    Plants affected

    Cabbages, cauliflowers, kale, rape, spinach, Brussels sprouts, turnips, broccoli, mustard, other cabbage family crops, radishes, swedes and some weeds.

    About Mealy cabbage aphid

    • Aphids are usually found on the youngest leaves and shoots, or on the heads of cabbages.
    • The undersides of more mature leaves will also be affected when infestations are large.
    • Adult aphids are up to 2mm long and elliptical in shape. They are mainly green in colour although their waxy coating gives them a powdery grey appearance.
    • During the warmer months aphids give birth to as many as five live young a day so rapidly produce large colonies.
    • When the colonies become over populated, they move to different locations by producing winged aphids.
    • During the autumn, aphids mate and produce eggs which overwinter.
    • Mealy cabbage aphids can damage plants in two ways, either directly by piercing the leaf with their feeding tubes and sucking the sap, or indirectly by infecting the plant with a virus.
    • Aphid-transmitted viruses can often result in deformed and stunted plants.
    • Aphids feed on plant sap, and excrete plant sugars as honeydew
    • Honeydew often covers the leaves of a plant and then becomes infected with unsightly black sooty moulds.

    Treatment

    Chemical

    Products containing the following chemical ingredients are all effective on Mealy cabbage aphid

    Pyrethroids and Pyrethrin

    Organic

    • Regular and thorough observation of plants.
    • Spray infested areas with a firm jet of water.
    • Spray with natural fatty acids, for example insecticidal soap.
    • Netting and fleece can be used to stop the aphids spreading.
    • For outdoor plants, aphid predators such as ladybirds, hoverflies, lacewing larvae and parasitic midges called aphidoletes, can be released onto affected plants.
    • For greenhouse plants in a contained environment, parasitic wasps such as Aphidius colemani and Aphidius ervi can be used.

    Prevention

    • Regularly check plants for signs of aphid infestation and deal with them as soon as they appear.
    • Encourage natural enemies like ladybirds, hoverflies and lacewings to become established in the garden by planting daisy-like flowers, yellow flowers and in particular, the poached egg plant Limnanthes douglasii.
    • Avoid using broad spectrum insecticides which will kill beneficial insects as well as aphids.
    • Encourage insect-eating birds such as blue tits, by hanging feeders during the winter months and nest boxes in the spring.
    • Maintain a weed-free environment around the brassica plants and collect and destroy all shed leaves.

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