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Cabbage whitefly

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last updated Mar 27, 2013
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Cabbage whitefly (Aleyrodes proletella) on Cabbage (Brassica sp.). Credit: RHs/Science.

Cabbage whitefly is a frequent pest on brassicas in allotments and gardens but not necessarily a serious problem.

What is cabbage whitefly? Back to top

Cabbage whitefly is a sap-feeding insect that can infest cabbage and all other types of leafy brassica. It is particularly a problem on kale, as the pest develops on the foliage that is destined for our dinner plates.

Symptoms Back to top

  • White-winged insects, 1.5mm long, that fly up in clouds from the underside of brassica leaves when disturbed
  • Flat, oval, whitish-green scale-like nymphs are attached to the lower leaf surface
  • Black or greenish-grey sooty moulds can develop on the upper leaf surface on the sticky honeydew excreted by this pest

Control Back to top

Brassica leaves are waxy and this makes them difficult to wet with a spray. Fortunately, because whitefly causes little real damage, infestations can be tolerated. Kale is the plant most affected by this pest as the insect occurs on the young leaves that are going to be eaten. On cabbage, brussels sprout, cauliflower and broccoli, the edible parts are little affected. 

Non-chemical control

Cabbage whitefly is not attacked by the Encarsia parasite sold for use against glasshouse whitefly but there are some other Encarsia species that occur in Britain that develop as larvae in cabbage whitefly nymphs. They are not commercially available but are sometimes sufficiently numerous in gardens and allotments to be effective in keeping cabbage whitefly at a low level. The use of relatively persistent pesticides, such 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 biocontrols.

Short persistence organic pesticides that can be sprayed onto the lower leaf surfaces include:

  • Plant oils (eg Vitax Organic 2 in 1 Pest and Disease Control, Scotts Bug Clear for Fruit & Veg)
  • Fatty acids (eg Bayer Organic Pest Control, Doff Greenfly and Blackfly Killer)
  • Plant extracts (Agralan Whitefly Killer)
  • Pyrethrum (Py Spray Garden Insect Killer concentrate, Scotts Bug Clear Gun for Fruit & Veg, Growing Success Fruit & Veg Bug Killer)
  • Several applications of these mild contact insecticides will be necessary to reduce a heavy infestation

Chemical control

  • If a damaging infestation of cabbage whitefly has developed, use deltamethrin (Bayer Provado Ultimate Fruit & Vegetable Bug Killer) or lambda-cyhalothrin (Westland Plant Rescue Fruit & Vegetable Bug Killer)
  • No more than  two applications of these insecticides are permitted on brassicas during the growing season (but up to three for deltamethrin on cauliflower, broccoli, kale and chinese cabbage). There is a seven-day harvest interval for these two insecticides

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology Back to top

Cabbage whitefly is present on its host plants throughout the year and overwinters as adult insects.

  • The adults lay eggs on the lower leaf surface, from which hatch the scale-like nymphs
  • Both adults and nymphs suck sap and excrete a sugary substance (honeydew) that allows the growth of sooty moulds
  • Brassicas are tolerant of the pest and even heavy infestations have little impact on plant growth, but sooty mould can be a problem, especially on Brussels sprout buttons and the leaves of kale
  • Although similar to glasshouse whitefly, cabbage whitefly is a different species and does not attack plants other than brassicas
  • Similarly glasshouse whitefly will not infest brassicas

Quick facts

Common name Cabbage whitefly
Scientific name Aleyrodes proletella
Plants affected: All leafy brassicas, including kale cabbage, broccoli and Brussels sprout
Main symptoms: Small white winged and scale-like insects on the underside of leaves. Sooty moulds may develop on the upper leaf surface
Most active: All year round

 

 

 

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