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Whiteflies
They look like little moths, but they aren't - not even closely related. They hide in vegetation and when disturbed they take off in a white cloud, only to settle back down as quickly. They are whiteflies, the scourge of greenhouse production everywhere.
To the home gardener, they are usually nothing more than a nuisance.
There are about 20 species of whitefly in Australia. The greenhouse whitefly (Trialeurodes vaporariorum) has the biggest host range, including tomatoes and beans.
There is also an azalea whitefly (Pealius azaleae) which is found on rhododendron species, a specific Australian citrus whitefly, and even one the lives on ferns.
Description
The whitefly belongs to the Order Hemiptera, which includes aphids. The adults have a wingspan of about 3mm and are covered in a powdery wax. They congregate on the underside of leaves, and suck sap.
The eggs (each female can lay about 200) are usually deposited on the underside of leaves, in a pattern or randomly, depending on the species.
Control
Small populations can be ignored, especially on ornamentals in the garden, although whitefly can be guilty of spreading plants viruses. They also exude a honeydew, on which sooty mould grows.
If populations are a big nuisance, try sticky traps. Whiteflies are attracted to bright orange-yellow. This colour is painted on boards (cardboard or something longer lasting about 300 mm square), and then coated with something sticky like oil. The insects fly onto the boards and remain stuck. Clean and reapply the oil as necessary.
Handpicking older leaves will remove young whitefly stages.
Avoid the use of a lot of nitrogen fertiliser, including manures. The succulent growth is very attractive to the insect.
One of the SGA staff, Julian, reports on the SGA gardening forum some good advice: Use a dustbuster! Click here to view the entire discussion.
A conventional vacuum cleaner is also acceptable. Don't worry about what the neighbours think!
There's no doubt, though, that the best defence is biodiversity, as also discussed on the forum by Marika. Populations of whitefly build up in greenhouse environments where one sort of crop is grown in large volumes.
In the garden, this is usually not the case, except with vegetables, in which case it's wise to intersperse with pest repellant plants (click here for the Pest Repellant Plants information sheet).
Production greenhouse operators often use the parasitic wasp Encarsia formosa to control greenhouse whitefly. This control method really only suits an enclosed environment.
This photograph (right) shows adult whitefly and Encarsia formosa wasp laying its eggs in a whitefly nymph (parasitized nymphs turn black), are courtesy of Biological Services
Silver Leaf Whitefly
Gardeners in Queensland, northern NSW and parts of Western Australia should be vigilant for a newly introduced whitefly, the silver leaf whitefly.
Since its arrival in Australia in 1994, silver leaf whitefly has spread quickly and is now causing severe problems, especially for vegetable and soybean producers in most parts of Queensland and for cotton growers in the NSW's Central Highlands where it threatens the viability of the area's cotton production.
The pest is still spreading, with recent outbreaks occurring in the Carnarvon area of Western Australia and the Darling Downs of Queensland.
What to look for
The distinguishing feature between this and the common greenhouse whitefly is the way the wings are held. The silver leaf whitefly holds its wings tent-like, whereas the greenhouse whitefly lies them flat over its abdomen and partly overlapping.
Adult greenhouse whiteflies are much larger than silver leaf whitefly, which are around 1mm long. Silver leaved whitefly feed and lay eggs on the underside of leaves. Adults can be found on any leaves.
Control
The silver leaf whitefly develops resistance to insecticides rapidly, so control using insecticides is generally unsustainable.
The use of natural enemies is considered one of the main ways to manage this whitefly. The introduction of exotic parasitoids are part of biological programs that have proven successful in parts of the USA. In these places the predatory agents have reduced the impact of the whitefly considerably.
Further information sourced from: What Garden Pest or Disease Is That? By Judy McMaugh, published by New Holland.
Click here to return to the list of info pages
The information contained on this page is Copyright © SGA and intended for personal use only.
You may not use the information for any other purpose without the express written permission of SGA.
