Whitefly
Trialeurodes vaporariorum
Role in the garden
Small white insects that suck the sap under the leaves and deposit a honeydew conducive to sooty mould.
How to attract / manage it
Yellow sticky traps; in a greenhouse, French marigold, basil and nasturtium planted near tomatoes slowed whiteflies in a trial (Conboy et al., 2019).
Practical guide
Where to find them
Greenhouse crops mainly (tomato, cucumber, aubergine), sometimes cabbages outdoors.
Prevention
Ventilate the greenhouse, plant basil or French marigolds nearby, set up yellow sticky traps from the start of the crop.
Early signs
A cloud of small white flies that take off at the slightest contact with the foliage; sticky honeydew and sooty mould on the lower leaves.
Action / control
Yellow sticky traps. Releases of beneficials (Encarsia formosa). Insecticidal soap (black soap) under the foliage, at the dose on the label (UC IPM).
Sources
- RHS (Royal Horticultural Society) : Glasshouse whitefly (rhs.org.uk/biodiversity/glasshouse-whitefly)
- UC IPM (université de Californie), Pest Notes : Whiteflies (ipm.ucanr.edu)
- Conboy, N.J.A. et al. (2019). Companion planting with French marigolds protects tomato plants from glasshouse whiteflies through the emission of airborne limonene. PLOS ONE, 14(3), e0213071.
- van Lenteren, J.C. (2012). The state of commercial augmentative biological control: plenty of natural enemies, but a frustrating lack of uptake. BioControl, 57(1), 1-20.
Favourite plants / resources
Related plant entries
Tomato
Central plant of the tomato guild. The neighbouring basil is reputed to hinder aphids through its volatile compounds.
Cucumber
A trailing cucurbit cross-pollinated by bees and bumblebees. Sow in pots in April or in place after mid-May; staking is essential beyond 1 m. Prone to leaf spot and downy mildew in late summer, water at the base only, mulch abundantly, space plants 60-80 cm apart.
Cabbage
A brassica with a long rotation: 4 to 5 years between two brassicas, 8 to 10 years after a clubroot attack (Réussir Fruits & Légumes, 2022), whose spores (Plasmodiophora brassicae) can contaminate the soil for up to 20 years (RHS). Very greedy (nitrogen, calcium, water). To be planted after a legume to benefit from the nitrogen.
Aubergine (eggplant)
A tropical nightshade that needs a lot of warmth (>20 °C at night), often grown in a cold greenhouse in northern France. Vibration-pollinated (buzz) by bumblebees, hence the value of attracting them. High demand for water and nutrients. Against Meloidogyne nematodes, the French marigold (Tagetes patula) only works as a dedicated, dense crop over a whole season, not as a mere border (see its fact sheet).