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Individually, whiteflies are just a few millimetres from head to tip of tail
- about the size of a pinhead! They usually fly around in clouds when disturbed,
and otherwise, are happy to carry on sucking the sap out of your plants from the
underside of the leaves. Unmistakably white, they are shaped like miniature
moths.
As well as sucking the sap out of plants, they excrete a sticky
honeydew - typical of aphids to which they are related. The honeydew in turn
attracts sooty mould and other fungal diseases.
Whiteflies are not the easiest of insect pests to control, so prompt
action is required as soon as any are found. It will probably need several
applications of a suitable insecticide, and the manufacturer's spraying
schedule should be followed.
Systemic insecticides are best. Insecticides containing Permethrin or
Bifenthrin seem to do the trick. If the infestation is on edible plants or
vegetables - and in particular they can be a plague on Brassicas - then
Bifenthrin would be the preferred option. Again, follow the manufacturer's
recommendations regarding cropping periods after application. Some types
of Whiteflies have developed a resistance to certain chemical sprays,
making them very difficult to control. If you have ongoing problems with
whiteflies, then try alternating the type of chemical spray.
Whitefly in the Greenhouse
Fuchsias in particular are susceptible to whitefly attack - especially
when grown under glass - or indoors. In the greenhouse, there are
biological controls available. Another option is to 'catch' the whitefly
with sticky yellow flycatcher cards.
If there is a severe infestation, then a great way of reducing the
numbers in a short time, is by the use of a portable vacuum cleaner - such
as a CarVac. Woks wonders until you can get the other orthodox
controls taking effect.
Don't ignore whiteflies. They will not simply go away! Be vigilant as
soon as plants break into leaf right after the winter break, and also
inspect the undersides of leaves for whitefly during mild winter periods.
A wide range of plants are susceptible to whitefly attacks including
Fuchsias, Brassicas, Dahlias, and more or less any crops grown under
glass. Mottling or yellowing of leaf surface is often the first sign of an
infestation, as the juveniles hatch from the eggs laid on the underside of
leaves and start to tuck into the ready supply of food! A\parasitic wasp -
Encarsia formosa - can be successful for commercial applications. This
avenue seems to be less successful with whitefly infestations in domestic
situations.
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