Greenhouse whitefly

Adults:

• about 1.5mm long
• hold their white powdery wings flat, almost parallel to and obscuring the body when viewed from above.

Nymphs:

• pale yellow-green
• scale-like
• long hairs protruding all over the body
• most nymph stages are immobile.

Silverleaf whitefly

Widespread; common in horticulture.

Cotton, sunflower, soybean, navy bean.

• Adults and nymphs suck on sap and excrete honeydew which interferes with photosynthesis and discolours the lint in cotton.
• A secondary infection develops when a sooty black mould fungus grows on the sticky honeydew.
• Under very heavy infestations, plants lose vigour causing leaf-wilting and failure to set seed.

The greenhouse whitefly breeds throughout the warm months with a life cycle of about 5–7 weeks. It can have up to 3 generations on a sunflower crop and 7 generations per year. Summer and autumn are risk periods, with outbreaks favoured by warm weather and host availability.

• Usually found on the lower leaf surface.
• Affects all crop stages.

Parasitic wasps (Encarsia formosa and Eretmocerus spp.) usually provide effective biological control.

Predators include small predatory bugs, lacewing larvae and ladybirds.

A management strategy needs to preserve and promote the activity of predators and parasites. Avoid early season use of broad spectrum insecticides, particularly pyrethroids and organophosphates.