Whiteflies

This page provides an overview of whitefly pests in vegetable crops. The related tools listed at the end of the page provide detailed information about their identification, damage and management. It is important to be able to identify insect pests such as whitefly, and to have unknown species expertly identified so that they can be appropriately managed.

Whitefly – an overview:

Whiteflies are small sucking insect related to aphids, leafhoppers, and mealybugs. They are usually found on the undersides of young leaves and have the capacity for rapid reproduction when conditions are favourable. When leaves are disturbed in infested crops, clouds of white flying insects indicate their presence.

Warm weather, nearby whitefly host crops or weeds and poor hygiene in protected cropping structures increase the risk of whitefly infestation. They can infest a large range of vegetable crops. Whitefly spread with infested plant material and attached to equipment and people.

Whitefly as sap suckers

Whitefly can damage plants by sucking sap from the plants, causing reduced growth, leaf yellowing, stunting, and yield reduction. Damage is similar to that caused by aphids. Sticky, sugary secretions called honeydew from whitefly can result in the development of sooty mould, which in turn affects the photosynthetic (food-producing) abilities of the leaves. Adults and nymphs are usually found feeding on the underside of leaves.

Whitefly as virus vectors

Whitefly adults are an important vector or carrier of viruses which can result in enormous economic losses in vegetable crops.

Whitefly species, hosts and damage

There are two main types of whitefly: Silverleaf whitefly (SLW) and Greenhouse whitefly (GWF). A new whitefly – Bemisia tabaci Q biotype – has been found in Queensland vegetable crops. As with SLW (B biotype), Q biotype whitefly can transmit viruses, including the ToTV. SLW favours warmer and drier environments (25°C to 30°C) and has the capacity to breed more quickly than GWF. GWF prefers temperatures of 20°C to 25°C.

Whitefly species	Vegetable host crops	Appearance	Primary damage
Silverleaf whitefly (SLW) (Bemisia tabaci Biotype B)	Cucurbits; capsicum; tomato; eggplant; brassicas; lettuce; sweetpotato; beans; beets.	Adults are 1.5 mm long, with powdery white wings (held at a slight angle) and a yellowish body.	Injects toxic saliva while feeding, causing silvering of leaves in cucurbits and irregular ripening and blotching in tomato. Produce honeydew, reducing plant vigour. Important vector of TYLCV and ToTV.
Greenhouse whitefly (GWF) (Trialeurodes vaporariorum)	Greenhouse vegetables; leafy vegetables.	Adults have white wings held flat and roof-like over the body.	Plants may wilt, turn yellow, drop leaves and have reduced growth rates. Produce honeydew, reducing plant vigour. Important virus vector of BPYV and ToTV.

Pest management

Integrated Pest Management (IPM) combining cultural, biological and chemical methods should be used to manage whitefly. Regular monitoring is important for decision making. Cultural practices that help to reduce or eliminate insecticide use is encouraged as these pests, particularly the SLW, rapidly develop resistance to insecticides. Long term SLW management requires an area-wide management approach, involving host-free periods and insecticide resistance management strategies.

Cleaning up property

Get rid of broadleaf weeds and the remnants of harvested crops. Weedy areas and crop residues can be often neglected and provide a perfect breeding ground for whitefly. Host weeds include sow thistle, bell or cow vine, jute, wild sunflower, and burr-gherkin.

Crop-free summer break

Adopting a susceptible crop-free summer break (early December to early February) will prevent the continuous availability of host plants for SLW. If adopted on a large-scale, such a gap in production reduces SLW numbers and lowers the risk of widespread insecticide resistance development.

Seedlings free of pest

Seedlings are a major means for spreading whitefly into new plantings. Young plants are generally more susceptible to damage and so early infestations need to be avoided. Clean seedlings should be always used against this damaging pest, as well as others such as the western flower thrips (WFT).

Use sticky traps

Yellow sticky traps can be used to detect and monitor whitefly activity, but should not be used to make spray application decisions. Traps should be changed each week and the total flies counted. Around 3–5 traps should be placed in a block of 2–3ha, level with the tops of the plants since SLW are most attracted to young foliage.

Field sampling

Whitefly adults and eggs are mostly found on the underside of young leaves while larger nymphs are most obvious on older leaves. The presence of large numbers of red-eyed nymphs indicates that adult SLW numbers have the potential to increase rapidly within the next 2–3 days. Adults should be sampled early morning and the edges of the field are usually infested first if the adults are moving into the crop from infested areas outside fields.

Biological control methods

Releasing parasitic wasps to attack whitefly can serve as a valuable management tool. Eretmocerus hayati can manage SLW, while Encarsia spp. species attacks both SLW and GWF.

Chemical controls

When whitefly numbers reach a point where insecticides must be used in order to avoid significant damage, this is known as the ‘action threshold’. The secret to effective whitefly management is to apply controls immediately when numbers reach this level. Systemic insecticides applied as seedling drenches or pre-plant soil applications can be effective for SLW control. SLW has developed a high level of resistance to some insecticides.