Check susceptible plants frequently from spring onwards so action can be taken before a damaging infestation has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (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.
Due to this insects rapid reproductive rate and the widespread occurrence of pesticide-resistant strains, biological control often gives better results than insecticides on greenhouse plants.
This involves introducing tiny parasitoid wasps, Encarsia formosa, which prey on the whitefly scale nymphs. The parasitoid is available by mail order from the Biological control suppliers . It is important to introduce the parasitoid before plants are heavily infested as it cannot give instant control. Parasitised whitefly nymphs turn black so it is easy to monitor the progress of the control. As Encarsia is killed by most insecticides, avoid spraying with products other than fatty acids, plant invigorators, plant extracts or plant oils (see below) prior to its introduction.
Other non-pesticide controls
- Hang sticky yellow sheets (widely available from garden suppliers) above or among the plants to trap adult whitefly, this can help monitor whitefly activity rather than give control
- Glasshouse whitefly can feed and breed on weeds so good weed control inside and around the glasshouse will remove alternate host plants
- Watch for signs of whitefly on new purchases as the insect is often first brought into a glasshouse on new plants. If possible quarantine new plants in order to give eggs and nymphs a chance to develop and be recognised
- Good ventilation will help to check the growth of sooty moulds
- Cleaning glasshouses in winter can help reduce overwintering populations
Glasshouse whitefly often requires repeated treatment to control infestations
- Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear for Fruit and Veg) 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, RHS Bug and Mildew Control, SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These 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)
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
Follow label instructions when using pesticides. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval. Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.
Pesticides for gardeners
Biological control suppliers