What is cabbage whitefly?
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.
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.
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
- 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
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)