Whiteflies are

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.

• 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 insect
• Cabbage whitefly should not be confused with glasshouse whitefly or viburnum whitefly which are not found on brassicas

Check brassicas frequently so action can be taken before a damaging infestation has developed. When choosing management options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section and avoiding pesticides. Within pesticides the shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached. 

Non-pesticide control

• Tolerate the presence of cabbage whitefly, with the exception of plants where young leaves are consumed such as kale it does not normally affect edible parts
• Encourage parasitoid wasp predators.  Cabbage whitefly is not a host of the biological control, Encarsia formosa parasitoid 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 can be numerous and keep cabbage whitefly at a low level. The use of pesticides will be harmful to these parasitoids and can allow a resurgence in the whitefly population that is able to reproduce without its numbers being reduced by these natural enemies
• Encourage predators and other natural enemies of whitefly, in the garden, such as ladybirds, wasps and ground beetles.

Pesticide control

• Complete eradication of cabbage whitefly is neither feasible nor necessary as it is only large populations that are likely to cause sooty mould. The immature stages of cabbage whitefly are not very susceptible to insecticides and so several applications may be needed to reduce a large population. 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.
• Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear Fruit & Veg, Vitax Rose Guard) can give good control of whitefly. These pesticides have a very short persistence and so may require reapplication to keep whitefly numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults
• Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action against aphids (e.g. Ecofective Bug Control, Growing Success Bug Stop, Rose Clear 3 in 1 Action SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These products contain some synthetic ingredients and so are not considered organic
• More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
• A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
• The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available

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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 this insect and it usually has little impact on plant growth, but sooty mould can be a problem, especially on sprout buttons and the leaves of kale
• Although similar in appearance to glasshouse whitefly, cabbage whitefly is a different species and does not feed on plants other than brassicas
• Similarly glasshouse whitefly will not feed on brassicas out of doors