Red spider mite (two-spotted spider mite)
Tetranychus urticae
Role in the garden
A tiny mite (about half a millimetre) that pierces the leaf cells in hot, dry weather: the foliage becomes speckled, greys and dries out, sometimes under fine webs.
Activity period
June to September in the garden; all year round under glass and indoors
How to attract / manage it
Mist the foliage, shade, predatory mites (Phytoseiulus persimilis), black soap.
Practical guide
Where to find them
Under the leaves, first on plants stressed by heat and drought: beans, cucurbits, tomatoes and aubergines, strawberries, greenhouse and house plants. Under a hand lens, minute yellow, green or orange-red moving dots.
Prevention
Avoid water stress (mulch, regular watering), ventilate and shade the greenhouse in the hot hours, mist the foliage in the evening during heatwaves (the mite hates humidity), do not treat with broad-action insecticides, which wipe out its natural predators.
Early signs
Fine yellow speckling on the upper side of the leaves, a leaden-grey then bronzed look, leaves drying out; at an advanced stage, thin webs between leaves and stems.
Action / control
Hose down the undersides of the leaves vigorously, spray black soap or an approved oil under the foliage several times, introduce the predatory mite Phytoseiulus persimilis in the greenhouse, remove and dispose of badly affected leaves.
Sources
- RHS : Glasshouse red spider mite (rhs.org.uk)
- UC IPM, Pest Notes : Spider Mites (ipm.ucanr.edu)
- INRAE, Ephytia : Tetranychus urticae (tétranyque tisserand), fiches Hypp et Biocontrol
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.
Courgette (zucchini)
A cucurbit (Cucurbita pepo) with separate male and female flowers on the same plant, dependent on bees and bumblebees for cross-pollination, hence the value of companion flowers nearby. Sow in pots in April or in place after the last frosts (mid-May), in rich soil well supplied with compost. Its large leaves quickly cover the ground and limit weeds; mulching and watering at the base (never on the foliage) slows the powdery mildew common in late summer. Harvesting young and regularly keeps production going.
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.
Bean
A nitrogen-fixing legume: in symbiosis with Rhizobium bacteria housed in its root nodules, it fixes nitrogen from the air, first for itself; part of it returns to the soil as its roots and haulm decompose, mainly benefiting the following crops. It belongs to the Three Sisters: maize serves as its stake and squash blankets the ground at its feet. Climbing varieties occupy the vertical layer while dwarf ones fill the low storey, two ways of inhabiting the bed. Its flowers feed bees and bumblebees, and at season's end, cutting the plants at the collar and leaving roots and haulm in place returns part of the nitrogen to the soil; the nitrogen in the seeds leaves with the harvest. Grown ahead of hungry vegetables, it readily opens a rotation.