These common sap-feeding garden pests mainly affect houseplants and greenhouse plants. They are a sub-tropical pest, introduced into the UK by accident.
Now over 1,400 species of whitefly have been recorded worldwide, 56 of which have been found in Europe. Known to thrive in the warm environment of greenhouses, the glasshouse whitefly causes yellowing and often disfigured leaves.
How to spot glasshouse whitefly
Whitefly are about 1.5mm long and they can be easily seen, especially if a plant is disturbed - you will see clouds of small white-winged insects flying up. They lay their eggs in a circular or crescent pattern on the undersides of leaves. Eggs are cone-shaped and are from dark gray to burnt orange. When the eggs hatch in 4-12 days, what emerges is a white, legless, oval shaped nymph.
Whiteflies weaken plants and make them vulnerable to further attacks from other pests and diseases.
Glasshouse whitefly excrete sticky honeydew deposits as they feed, which fall on to the surrounding foliage. This causes a dark sooty mould to develop on the leaves. It is important to keep a close eye on your greenhouse vegetables like cucumber, melon, tomato, and peppers. Outdoor plants are also affected, but not as severe as greenhouse plants.
How to treat whitefly
Squash the eggs if you see them on the leaves. Try tapping the leaves of infected plants and, using a vacuum cleaner, suck up the clouds of whitefly as they fly up. Alternatively, spray plants with soapy water or purchase yellow sticky strips which attract the flies and causes them to stick to the card.
A natural method for getting rid of whiteflies is using nature's own predator, the Encarsia parasite. These tiny parasitic wasps search for fresh whitefly larvae and lay their eggs amongst them. The Encarsia larvae develop inside the scales, killing the Whitefly larvae and turning them black.
If you use this method then don’t trim off any plant material with black scales on it or you will be throwing out valuable parasites. It is also important to avoid spraying insecticides when using this biological control, as most insecticides will kill off the Encarsia parasite too.