Find out you can cope with whitefly infestations in your garden.

Whitefly

Is your garden infested with whiteflies? If you are not sure, look out for leaves that are white to silverish with small black dots. Whitefly infestations mainly occur on those plants cultivated under cover. However, in gardens, onions, peas and fuchsias seem to be particularly vulnerable. Outdoor whitefly infestations commonly occur during extended warm, dry spells. However, the damage done during these infestations is usually not too serious.

Whiteflies are close relatives of the woolly aphid and scale, and they look somewhat like minute moths. The adult flies are approximately 2mm long with four winglets. Their bodies and wings are coated with a white waxy dust, which gives them their characteristic dusty-white appearance.

The adult female deposits 2-3 eggs daily on the underside of leaves and, during her adult lifespan, she will lay up to 150 eggs. The yellowish-green, transparent, flat larvae will hatch after a couple of days. The adult whiteflies and their larvae remain on the underside of leaves and weaken plants by sucking sap. Whiteflies thrive under greenhouse conditions and can be ‘imported’ into the house and garden by plants cultivated under cover. Plants especially vulnerable to whitefly attack are tomatoes, cucumbers, beans, geraniums, fuchsias and species of lantana. The whiteflies that attack the various species of brassicas are especially persistent.

Controlling whitefly

In Europe, whitefly attacks in greenhouses are controlled by releasing predator wasps (Encarsia formosa), which are commercially available at nurseries. The released female wasps lay eggs in the whitefly larvae and the wasp larvae, in turn, feed on the whiteflies. Unfortunately, commercially grown predators are not yet available in South Africa.

Whiteflies are strongly attracted to anything yellow. Cut a square piece of card or plastic, paint it bright yellow or, alternatively, coat thinly with old grease and hang amongst the affected plants. The whiteflies will be attracted to the yellow board or, if they land on the greasy cardboard, they will be trapped by the grease.

For severe attacks, spray with a systemic insecticide. As the nymphs hide on the underside of leaves, ensure that you spray both sides of the leaves. Spray twice at an interval of three days. Thereafter, spray the plants with a tissue strengthening spray such as kelp spray. Rhubarb planted in the greenhouse or in the garden will repel whiteflies, as they dislike the smell of rhubarb plants.