Two-spotted spider mite: how to recognise and treat it

Pest

Symptoms

Fine pale stippling or mottling on the upper leaf surface; leaves may turn bronze.
Tiny yellowish-green mites with two dark patches, white cast skins and eggs on the leaf undersides — easiest to see with a 10× hand lens.
Fine silk webbing over leaves and shoot tips in heavy attacks.
Leaves turn yellow or reddish, dry up and drop; badly attacked plants weaken and may die. Worst in hot, dry, dusty conditions.

Spray the leaf undersides forcefully with water, at least once a day while mites are present.
Insecticidal soap or horticultural or plant oil (such as neem) covering the leaf undersides completely; test on one plant first, and do not spray water-stressed plants or in great heat.
In a greenhouse or conservatory, release the predatory mite Phytoseiulus persimilis; Amblyseius californicus or the predatory midge Feltiella acarisuga also help.

Sulfur sprays on plants the label allows — not on cucurbits, not above 32 °C and not within 30 days of an oil spray; avoid pyrethroids and carbaryl, which kill mite predators and can make outbreaks worse.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Keep plants well watered — drought-stressed plants suffer most.
Keep dust down with mulch and regular watering, and rinse dusty foliage; in greenhouses raise humidity by damping down, which lowers the risk but does not control mites on its own.
Check leaf undersides with a hand lens from spring to autumn, and remove badly infested plants from the greenhouse in late summer.
In winter clear plant debris, old canes and ties from the greenhouse, clean it, and control weeds in and around it.

Figures checked against these sources.