The glasshouse whitefly is a small white flying insects which lays eggs on the undersides of leaves. It is usually found indoors. Whitefly are fairly inactive in cool temperatures over Winter, but multiply very quickly in warm Spring and Summer weather. They fly about at the slightest disturbance, and may even create ghostly white clouds in the air. They fly like tiny moths.
Remember whiteflies are nearly always moving. If you see white threads static on tops of the leaves, they are not whitefly but something else - very likely to be shed aphid skins dropped down from developing Aphid under leaves above. Or they could be thrips larvae. They are not "whitefly" unless body and wings are a ghostly white.
Whiteflies suck sap from their host plant and drop sticky secretions onto leaves below. Left uncontrolled Whiteflies overwhelm the plant, weakening it and flying around in huge numbers. Undersides of leaves become populated with Whiteflies adults and white eggs (scales).
The most effective treatment for whitefly is the parasite "Encarsia". It is supplied on small cards which can be hung up around your plants. For more information about Encarsia click here
Encarsia work best with temperatures above 21°C with 12hr+ daylight hours. Generally, this means introducing Encarsia from mid April to August, although it can be earlier or later with extra heat and light.
The Standard pack should give good control for an average conservatory or small greenhouse. You may benefit from a second batch two weeks later.
The Larger pack should be used if the Whitefly infestation is very bad or the area large. They will stay with their prey within a greenhouse, but are not suitable for applying outdoors.
More technical information about encarsia cards
Click here for closeup pictures of encarsia cards
Click here for information about Tobacco Whitefly