In the garden: A wide range of ornamental and edible plants
On Crops: A wide range of ornamental and edible plants
Throughout UK and Europe
The Greenhouse whitefly is a small sap-sucking insect that infests and feeds on the undersides of leaves. Adults resemble small white moths and are around 1.5mm in length. They are often found under the new tender leaves, either as mating pairs or as egg-laying females. Eggs are usually laid in circles as the female pivots around her feeding site. White wax is also deposited on the leaf where the eggs are laid. Initially the eggs are a pale yellow in colour but change to black just before they hatch. The small hatchling larvae are able to move around the leaf to find a suitable place to feed before shedding their skin and becoming immobile. They are pale green in colour and scale-like in appearance. For the rest of the larvae’s life it remains immobile on the underside of the leaf, attached by its straw-like mouthpart through which it sucks the plant sap. After two more skin sheds, the larvae swell and harden to become pupae from which the next generation adults emerge.
Infested plants can become weakened by the feeding of both adult and juvenile whiteflies. Leaves can also become contaminated with black sooty moulds that grow on honeydew excreted by the whiteflies.
Use a fine mesh netting to protect susceptible plants from adult whitefly. Yellow sticky traps can also be used to reduce adult whitefly numbers on plants.
Adult whiteflies are delicate insects that can usually be removed from plants with soap-based sprays. Juvenile whitefly can be controlled with predatory Coccinelid beetles, predatory true-bugs such as Macrolophus and parasites such as Encarsia formosa. As a last resort, both adult and juvenile whitefly can be controlled with organic approved Pyrethrum sprays that are available from garden product suppliers. These need to be applied following the label instructions.
Greenhouse whitefly can build up to extremely large numbers on outdoor strawberry, cucumber and pumpkin leaves. When the weather becomes cooler in early autumn, the adults disperse from outdoor crops to seek warmer environments. This is an important time to regularly check glasshouse crops for new whitefly invasions.