Cabbage whitefly

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

Cabbage whitefly (Aleyrodes proletella) on Cabbage (Brassica sp.). Credit: RHs/Science.

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

 

 

 

What is cabbage whitefly?

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

Symptoms

  • 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

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 by this pest as the insect occurs on young leaves that are going to be eaten. On cabbage, sprouts, cauliflower and broccoli, the edible parts are little affected.

Non-chemical control

Cabbage 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 reinfestation.  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 by this pest as the 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 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 thicloprid, 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.

Chemical control

Short persistence organic pesticides can be sprayed onto the lower leaf surfaces. These will have limited effects on natural enemies and have a one day harvest interval. Products include:

  • Plant oils (e.g. Vitax Organic 2 in 1 Pest and Disease Control,  Bug Clear for Fruit & Veg)
  • Fatty acids (e.g. Bayer Organic Bug Free, Doff Greenfly and Blackfly Killer, Doff Universal Bug Killer, Natures Answer Natural Fungus and Bug Killer) 
  • Natural pyrethrum/pyrethrins (e.g. Py Spray Garden Insect Killer concentrate, Bug Clear Gun for Fruit & Veg, Growing Success Fruit & Veg Bug Killer, Pyrol Bug & Larvae Killer) 

Several applications of these mild contact insecticides will be necessary to reduce a heavy infestation

Synthetic insecticides. These products have longer persistence and should only be used if a damaging infestation of cabbage whitefly has developed.  There are restrictions on the number of applications that can be made to food-plants and a longer harvest interval. The label instructions must be followed when applying these products to food plants.

Deltamethrin (e.g. Bayer Provado Ultimate Fruit & Vegetable Bug Killer) or lambda-cyhalothrin (e.g. Westland Resolva 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. Thiocloprid (e.g. Bayer Provado Ultimate Bug Killer Ready to Use) is limited to one application during the growing season and has a 14 day harvest interval 

Download

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

Biology

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 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

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