Whitefly are small winged insects, which fly up in clouds from the underside of the leaves of affected plants when disturbed. They suck the sap of plants, weakening the plant.
Whitefly set up home and live out their lives on the underside of leaves. As adults they are about 2mm long with white wings, which give them their name.
The female adults lay eggs that hatch into yellowy-green, scale-like nymphs that become pupae before reaching adulthood. This gives tree generations living under the same leaf and all of them feeding on the sap of the plant.
In the garden, whitefly are fond of a wide range of plants, including azaleas, rhododendrons, honeysuckle and vegetables including cabbages. Indoors, in the conservatory or in the greenhouse they’re less picky and will feed on many houseplants, ornamentals and vegetables.
There’s usually little visible damage to the plants themselves, but brush past an infested plant or close the greenhouse door sharply and you’ll see a ‘white cloud’ rise from the underside of the leaves. If the infestation is left untreated things change.
They feed on sap and they excrete a sticky honeydew that drops on to lower foliage. A black sooty mould develops, which is very unsightly. Whitefly can also spread plant viruses.
Pyrethrin-based and other naturally occuring insecticides will control whitefly. For best results, spray thoroughly as these insecticides only kill on contact.
For treatment of ornamental plants and certain listed fruit and vegetable crops (see the list on the product label), a systemic insecticide will provide more effective control.
In greenhouses and conservatories, yellow ‘sticky’ traps can help control as can the biological control encarsia - a tiny wasp that lays its eggs in the scale stage of the whitefly.