Organic Strategies for Whitefly Control
© Frances Michaels
Whiteflies suffer from an identity crisis, as they are not flies at all. they resemble tiny, pure white moths
but are, in fact, closely related to sap-sucking
. Cast-off aphid skins on leaves could
be mistaken for whitefly, but whitefly will quickly flutter up and fly away when disturbed, whereas the aphid
skins will simply drop off. Just shake the plant to find out which you have!
A Modern Pest
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
While there are about 20 species in Australia, the most serious pest is the greenhouse whitefly Trialeurodes
that 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 viruses.
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 eight 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 to 30 days, less in summer. Whiteflies have no hibernation
period and must have a suitable host all year. Severe winters reduce numbers considerably.
Physical and Cultural 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 85846977. It is most likely to be effective inside glasshouses rather than outdoors, Encarsia
wasps kill whitefly nymphs in one of two ways: they lay an egg inside the nymph, providing food for
their young, or they kill the nymph outright and feed on it. Once the whitefly nymphs are parasitised they
turn black and no longer feed.
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:
Least-Toxic Chemical Controls
- 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.
- At the beginning of the season, hang
sticky yellow traps
above the plants 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 avoid wearing yellow
clothing around whiteflies or you may carry them from plant to plant.
- Use a floating row cover such as a Vege Net
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, three days in a row.
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 and make sure you spray underneath the leaves. Sprays include:
Sticky Yellow Traps
- Potassium soap sprays such as
Nature's Way Vegie and Herb Spray
are a good choice of control for the home gardener; spray every two to three days for two weeks. Soap sprays
work by blocking the insect's breathing pores and dissolving its outer covering, resulting in dehydration.
They are considered very safe for the environment.
- Eco Oil is certified organic
and can be used to control a range of insect pests including whitefly. For best results, use it at the first
sign of infestation.
Eco Oil has an enhanced formulation
which helps to attract beneficial insects into the garden.
- Neem is a botanical insecticide made from extracts of the neem tree.
Eco-neem is a registered organic spray that controls
a wide range of insects including whitefly. It works in multiple ways with the two main actions being
suppression of insect appetite (they starve to death) and restricting growth (unable to moult successfully).
It is approved in Australia for use on ornamental plants only but would be particularly useful sprayed on a
trap crop of tall, lush grass. Research undertaken in New Zealand on neem's 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.
- Botanical insecticides such as garlic or a hot chilli spray are useful. You can try making these at home
yourself but always test the spray on one plant (the one you are least fond of) before spraying the whole
garden. Commercial formulations are less likely to burn the leaves.