Due to this pest's 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 parasitic wasps, Encarsia formosa, which attack the whitefly nymphs. The parasite is available by mail order from the suppliers of biological controls. It is important to introduce the parasite before plants are heavily infested as it cannot give instant control. Parasitised 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, urea/mineral lattice, plant extracts or plant oils (see below) prior to its introduction.
Other non-chemical controls
Hang sticky yellow sheets (widely available from garden suppliers) above or among the plants to trap adult whitefly. 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 pest 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.
Frequent sprays with contact insecticides deltamethrin (e.g. Bayer Sprayday Greenfly Killer), lambda cyhalothrin (e.g. Westland Resolva Bug Killer), pyrethrins (e.g. Py Spray Garden Insect Killer, Py Bug Killer Spray, Bug Clear Gun for Fruit & Veg, Defenders Bug Killer, Growing Success Fruit & Veg Bug Killer, Growing Success Shrub & Flower Bug Killer, Vitax House Plant Pest Killer, Pyrol Bug & Larvae Killer Concentrate), plant extracts (e.g. Vitax Organic Pest & Disease Control Concentrate, Bug Clear for Fruit & Veg, Agralan Whitefly Killer), fatty acids (e.g. Bayer Organic Bug Free, Bayer Natria Bug Control, Doff Universal Bug Killer) or products which contain a blend of surfactants and nutrients (e.g. SB Plant Invigorator) can control established infestations.
Resistance to pyrethrins, deltamethrin and lambda-cyhalothrin can occur. Products containing deltamethrin and lambda-cyhalothrin can be used on edible plants listed on the label provided the label instructions on maximum dose and harvest interval are followed.
Systemic insecticides can be applied as foliar sprays or compost drenches. Systemic insecticides are absorbed into the plant tissues and are taken up by sap-sucking insects when they feed. They also usually have some contact action. There are several formulations available.
- A compost drench containing thiocloprid (e.g. Bayer Provado Vine Weevil Killer 2) is for application to the roots of ornamental plants growing in pots or containers only
- Foliar sprays containing thiacloprid (e.g. Bayer Provado Ultimate Bug Killer) can be sprayed on the foliage of ornamentals and some edible plants (e.g. greenhouse-grown tomatoes, peppers, aubergine and cucumber) provided the label instructions are followed.
- Acetamiprid can be applied as a compost drench (e.g. Bug Clear Ultra Vine Weevil Killer) on container-grown ornamental plants, or as a foliar spray (e.g. Bug Clear Ultra or Bug Clear Ultra Gun) on ornamental plants only
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Biological control suppliers (Adobe Acrobat pdf document)