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How to Control Whitefly Without Harmful Pesticides

whitefly pest insect on leaf

Whiteflies are small white flying insects around 1mm long that prefer to hide on the undersides of young plant leaves, and when disturbed fly up in the air around the plant in a cloud of white flying insects, often in large numbers. They belong to the order Hemiptera (true bugs), family Aleyrodidae (Whiteflies), and are related to aphids, scales and mealybugs. 

There are many different species of whiteflies, including greenhouse whiteflies (Trialeurodes vaporariorum) and silverleaf whiteflies (Bemisia tabaci), and all species are considered pests. Whitefly attack a wide range of produce crops, ornamental plants and weeds, which serve as host plants that they can feed on.

These insects suck the sap from the leaf and excrete honeydew (the sugary sap of the plant minus the proteins which they ingest) which leaves the lower surface of the leaf sticky to the touch, much like aphids do, causing considerable damage in the process.

What Damage Do Whitefly Cause?

The loss of a plant’s nutrient-rich sap can weaken it and stunts its growth. Heavy whitefly infestations can cause discolouration of leaves, defoliation (leaf drop), deformities in leaves and fruit, a reduction in yields, and may even kill plants.

Whitefly can breed very quickly to produce large populations which can significantly impact plant health. Their eggs hatch after 5–9 days and whitefly can complete their lifecycle from egg to adult in 18–28 days in warm weather! Newly emerged females are ready to mate in 12–20 hours, can live up to 60 days, and breed several times during their short lifespan. As such, they can produce large populations in 3-4 weeks, and 8–12 overlapping generations within a year, that can cause considerable plant damage.

The honeydew that whitefly excrete on the surface of a leaf is a sugary liquid that attracts ants which interfere with the activities of natural predators that control whitefly and other pests. It can also attract black sooty mould in humid conditions. This mould grows and feeds off the sugars, smothering the leaf surface with a thick black coating that restricts plant photosynthesis, but can be washed off fairly easily.

These sap-sucking pests have needle-like mouthparts which can pierce the plant tissue to reach the flowing plant sap inside. Feeding this way, they also act as disease vectors, organisms that carry and transmit infectious pathogens, spreading viruses from plant to plant.

While feeding on plant sap, silverleaf whitefly also inject toxic saliva is into the plant which can cause physiological changes to plant tissue. Common symptoms include:

Whitefly Prevention Methods

While it may be possible to or tolerate small outbreaks of whitefly, controlling large populations of this pest is difficult, even with toxic pesticides! Prevention of the problem is a far better long-term strategy.

The best way to prevent whitefly populations explosions is by minimising conditions favourable to them, and instead promoting environment that are detrimental to them. This can be done in the following ways:

Biological Controls for Whitefly

In many situations, the natural enemies of whiteflies can do a sufficient job to control pest numbers without having to resort to chemical treatments. Outbreaks often occur when the populations of these beneficial insects are disrupted by the use of toxic insecticides.

Whiteflies have a range of natural enemies, such as ladybirds, lacewings, hoverflies, parasitic wasps such as Encarsia species, predatory mites such as Montdorensis species, and predatory bugs such as big-eyed bugs, and minute pirate bugs.

Encourage these beneficial insects by growing plants for the Asteraceae (daisy) and Apiaceae (parsley) family, and other companion plants such as Sweet Alyssum, all of which produce shallow flowers that can serve as a nectar source to provide an alternative food source when pest numbers are low.

Physical Whitefly Control Methods

Physical controls include manual methods such as hand removal of small pest infestations, pest infested leaves, or hosing pests off and traps such as sticky traps.

Organic Chemical Controls for Whitefly

There are environmentally safe pesticide sprays that can be used to control whitefly populations.

The fairly frequent application of these sprays is necessary to keep up with the very fast breeding cycle of the pest.

It is worth noting that both horticultural soap and horticultural oil work by smothering the insect and stopping it breathing, effectively suffocating it. Since they don’t work by chemical action like other pesticides, the pests can never develop resistance.

As a general precaution when using garden sprays, do not spray when shade temperatures are near 30°C or higher, or when the soil is dry and plants are suffering from moisture stress.

Whitefly Resistance to Toxic Synthetic Pesticides

Whitefly can quickly develop resistance to toxic pesticides, and many are already resistant to the most common ones, including some of the heavy-duty agricultural pesticides.

According to the New South Wales Department of Industry,
silverleaf whitefly arrived in Australia with resistance to synthetic pyrethroids, organophosphates, carbamates and insect growth regulators. Since their arrival, they’ve developed measurable resistance to endosulfan (similar to DDT and now banned), amitraz, bifenthrin and imidacloprid.

By using a combination of environmentally safe control methods together, the populations of whitefly can be reduced to such a low level where their impact will be negligible.


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