Thrips
Thysanoptera (Frankliniella occidentalis, Thrips tabaci)
Role in the garden
Thread-like insects of 1 to 2 mm that rasp the epidermis of leaves and flowers and suck up the contents: silvery patches dotted with black specks, distorted flowers. Thrips tabaci mainly attacks alliums, the western flower thrips greenhouse crops.
Activity period
May to September in the garden, earlier and later under cover
How to attract / manage it
Blue sticky traps, predatory Orius bugs, predatory mites, overhead watering on alliums.
Practical guide
Where to find them
Between the sheathing leaves of leek and onion, in the flowers and under the leaves of cucurbits, peppers and strawberries; very common in greenhouses in hot, dry weather.
Prevention
Mulch and water regularly (thrips thrive in the dry), encourage the predatory Orius bugs with pollen flowers (marigold, yarrow, phacelia), set blue sticky traps from spring under cover, rotate allium crops.
Early signs
Small silvery streaks and patches on the leaves, dotted with minute black droppings; leek and onion leaves marbled with white; distorted flowers and young fruit.
Action / control
Frequent sprinkling with water on alliums, black-soap sprays, releases of Orius laevigatus or predatory mites (Amblyseius) under cover, removal of badly affected leaves.
Sources
- INRAE, Ephytia : Thrips (fiches Tomate, Courgette & courges, Info-Insectes Thysanoptera)
- Ctifl : gestion du thrips du poireau, irrigation par aspersion et choix variétal
- RHS : Thrips (rhs.org.uk)
- UC IPM, Pest Notes : Thrips (ipm.ucanr.edu)
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.
Leek
A traditional ally of the carrot: its sulphur compounds are reputed to confuse the carrot fly (Psila rosae), on the model of the onion, whose effect has been measured (Uvah and Coaker, 1984). Earth up during growing to blanch the stem.
Onion
The sulphur compounds released by the bulbs are reported to repel several pests (the carrot fly in particular), an effect documented in the laboratory, moderate in the garden. Like the other alliums, tradition keeps it away from legumes, with no effect on their nodulation demonstrated in the field.