The adults are small white moth-like flies, 1mm in length. Eggs are laid on the undersides of leaves and hatch
in 8 days. Both newly hatched 'crawlers' and adults feed by sucking the sap from the underside of the leaf.
They also excrete 'honeydew' which causes problems with black sooty mould. After 4 nymph stages they form a
black pupa, visible as a small speck under the leaves. Most species can complete a full life cycle in 20-30
days, less in summer. Each adult female may lay 200 eggs. Egg laying increases in warm weather. Whiteflies
have no hibernation period and must have a suitable host all year. Severe winters reduce numbers
Suggested Organic Strategies:
- A parasitic wasp Encarsia formosa is commercially available as a biological control.
- Other predators include spiders, ladybird larvae, lacewings, hoverflies and damsel bugs.
- Sticky yellow traps
are useful at the beginning of the season.
- Vacuuming in the early morning when whiteflies are cold and slow-moving with a small hand-held battery
operated vacuum is useful particularly for the adults before a great deal of egg-laying is done. After
vacuuming enclose the section of the machine containing the bag with plastic and put in the freezer for
- Companion plants e.g.
nasturtium may help to repel the pest.
Organic Strategies for Whitefly Control
© Frances Michaels
Whiteflies suffer from an identity crisis, as they are not flies at all, in appearance they resemble tiny,
pure white 'moths' but are in fact, closely related to sap-sucking aphids. Aphid cast-off skins could be
mistaken for whitefly, but whitefly will quickly flutter up and fly away when disturbed, while the cast-off
aphid skins will drop off. Just shake the plant to find out which you have! While there are about 20 species
in Australia, the most serious pest is the greenhouse whitefly Trialeurodes vaporariorum
attacks a very wide range of plants including tomatoes and beans. Unfortunately, whiteflies don't go round
in ones or twos - they go round in hordes, so a severe attack can have a major impact on a plant.
Whiteflies suck sap from the plant, resulting in a yellow mottling on the surface of the leaf, as well as
leaf loss, wilting and stunting. Not only do they feed on plants, but they also produce honeydew, which
spoils the plants' appearance, attracts ants and black sooty mould. Whiteflies can also transmit plant
Adult whiteflies have a 3 mm wingspan and are covered with a white, waxy coating. Each adult female lays about
200 eggs on the underside of the leaves, the eggs hatch in 8 days. Newly hatched 'crawlers' or 'nymphs'
move around for a few days but then insert their feeding tube and lose their functional legs. At this stage
they can be confused with scale.
Most species can complete a full life cycle in 20-30 days, less in summer. Whiteflies have no hibernation
period and must have a suitable host all year. Severe winters reduce numbers considerably.
In many ways, whitefly is a modern pest, created by the over-use of pesticides that have killed off its
natural enemies. One study has even demonstrated an increased whitefly reproductive capacity when sprayed
with certain insecticides!
Physical and Cultural Controls
If you had clouds of whiteflies on your tomatoes or beans in the previous year, then acting early in the
spring is your best bet to control this pest! Useful strategies include:
- Vacuuming in the early morning when whiteflies are cold and slow moving can remove many of the adults
before they have a chance to lay many eggs. After vacuuming, empty the vacuum bag into a plastic bag and
put in the freezer for 24 hours.
- Hang sticky yellow traps
above the plants, at the beginning of the season to detect an invasion early. Tapping the plants with a
stick will cause the whitefly to fly up and onto the traps. Whiteflies are strongly attracted to the colour
yellow, so you really shouldn't wear yellow clothing around whiteflies or you may carry them from plant to
- Physical barriers such as floating row covers
or mosquito netting work very well for early-season protection.
- Handpick older leaves to remove young whitefly stages.
- Avoid using a lot of nitrogen fertilizer, including manures, as succulent growth will increase whitefly
populations. You may need to check your phosphorus and magnesium levels, as deficiencies in these are
believed to contribute to whitefly infestations.
- Try a high pressure hosing in the early morning, 3 days in a row.
Least-Toxic Chemical Controls
- Natural enemies of whitefly include small birds, spiders, lacewings, hoverflies, ground beetles, mirid
bugs and damsel bugs. The adults and larvae of some ladybirds also feed on whiteflies. Habitat, such as a
border of perennial plants, needs to be available all year round as a refuge for these predators.
- An important predator and parasitoid of whiteflies is the tiny wasp Encarsia formosa. It is
available commercially from
Biological Services, PO Box 501, Loxton,
SA 5333 Ph 08 8584 6977. It is most likely to be effective inside glasshouses rather than outdoors, Encarsia
wasps kill whitefly nymphs in one of two ways: they either lay an egg inside the nymph, providing food for
their young, or they kill the nymph right away and feed on it. Once the whitefly nymphs are parasitised they
turn black and no longer feed.
Whiteflies began showing resistance to synthetic insecticides many years ago, and have since become a major
problem in some crops and greenhouses. To control an infestation use a suitable organic spray as soon as adults
are noticed, make sure you spray underneath the leaves.
Pyrethrum Plus Garlic
Sticky Yellow Traps
- Insecticidal soap sprays such as
Natrasoap are a good choice of
control for the home gardener; spray every 2-3 days for 2 weeks.
- Spray Eco-Oil or try making
your own oil spray by mixing 1 tablespoon dishwashing liquid detergent with 1 cup of cooking oil; add 1 to
2.5 teaspoons of this solution to 1 cup of water, spray onto plants every 10 days.
- Botanical insecticides such as
pyrethrum plus garlic are useful.
Research undertaken in NZ on neemís effectiveness for
whitefly found that it had a major impact by preventing the 'nymph' stage from developing into an adult; the
nymphs tend to disappear from the treated plants.