Prevention and Protection Against Mites

The greenhouse whitefly (Trialeurodes vaporariorum) is one of the most serious pests, particularly on houseplants and in greenhouses.

They settle on the underside of leaves and suck plant sap. Infested leaves gradually die off. Additionally, whiteflies can transmit many viral diseases to plants.

Although they don't normally overwinter in our climate, in greenhouses and at room temperatures they can reproduce year-round.

Which plants do whiteflies attack?

In greenhouses, whiteflies are most commonly found on solanaceous plants, namely tomatoes, peppers and cucumbers. Among houseplants, those with thin leaf cuticles and not very glossy surfaces are at risk - these are easier for whiteflies to feed on. Whiteflies can also very often be found on ornamental plants - they particularly enjoy fuchsias, geraniums and gerberas.

Signs of whitefly infestation

If you notice that plant leaves are yellowing, becoming deformed or dropping off, simply look at the underside of the leaves. If you find approximately 2mm white or yellowish moths that briefly fly away when disturbed and then land again, these are whiteflies. They also excrete a sweet sticky liquid - honeydew. This clogs the plant's surface and prevents it from breathing and photosynthesising. Due to this and the weakening caused by sap-sucking, plants grow poorly, become stunted and can eventually dry out completely.

The liquid excreted by whiteflies can become food for saprophytic fungi - so-called sooty mould. These can cause black spots on the underside of leaves, but don't harm the plant themselves.

Prevention and protection against whiteflies

Whiteflies multiply in humid environments, so it's advisable not to overwater plants and to let the substrate dry out between waterings. Sticky traps also have their place, which besides providing protection also serve a monitoring function - based on the number of stuck whiteflies you can determine whether plants need to be sprayed with insecticides.

Chemical control involves spraying with insecticides, which should be carried out immediately after detection. Usually the spraying needs to be repeated several times.

In enclosed spaces, it's also possible to use the "parasitic wasp" - Encarsia formosa. Adults lay eggs inside whitefly larvae and effectively eliminate them.