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Cabbage whitefly are small white-winged insects that can be found on the undersides of brassica leaves. They are frequent found on brassicas in allotments and gardens but not necessarily a serious problem that requires control.
Cabbage whitefly (Aleyrodes proletella) on Cabbage (Brassica sp.). Credit: RHs/Science.
Cabbage whitefly is a sap-feeding insect that can infest cabbage and all other types of brassica. It can be a particular problem on kale, as the insect can develop on the foliage that is destined for dinner plates.
Cabbage whitefly can be difficult to control, particularly on allotments where there are likely to be affected plants on nearby plots that will be a source of re-infestation. Fortunately, cabbage whitefly only infests outer leaves and usually causes little real damage to parts of the plant that are consumed, therefore infestations can usually be tolerated. The immature stages in the life cycle are not very susceptible to insecticides and so several applications may be needed to reduce a heavy infestation. Complete eradication is neither feasible nor necessary as it is only heavy infestations that are likely to cause problems with sooty mould. Brassica leaves are waxy and this makes them difficult to wet with pesticide sprays. Kale is the plant most affected as this insect occurs on young leaves that are going to be eaten. On cabbage, sprouts, cauliflower and broccoli, the edible parts are little affected.
Cabbage whitefly is not attacked by the biological control, Encarsia formosa parasite sold for use against glasshouse whitefly (Trialeurodes vaporariorum) but there are some other Encarsia species that occur naturally in Britain that develop as larvae in cabbage whitefly nymphs. They are not commercially available but are sometimes sufficiently numerous to be effective at keeping cabbage whitefly at a low level. The use of relatively persistent pesticides, such as deltamethrin or lambda-cyhalothrin, will be harmful to these parasites and may allow a resurgence in the whitefly population that is able to reproduce without its numbers being reduced by these natural enemies.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Cabbage whitefly is present on its host plants throughout the year and overwinters as adult insects.
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