Red spider mite (Tetranychus urticae)
These tiny mites, which are light-green with two darker spots on their backs in summer, only mature to red in autumn and winter. They feed on the undersides of leaves, killing cells which gives leaves a distinctive mottled apperance. In serious infestations, they spin a fine web for protection and to help them migrate to nearby plants. The dry conditions they require are mostly found under glass where they can be a serious problem. However, they can also affect outdoor crops in dry conditions. They overwinter as adults in cracks and crevices in greenhouses, emerging in Spring to lay eggs.
- Mottling and yellowing of leaves with silvering and silky webbing when advanced.
- Badly affected leaves may fall.
Prevention & control
- Give greenhouses a thorough clean over winter to clear the hibernating adults out of their hiding places
- Regular misting (twice daily) may be enough to control them
- If not, wash off with a water and insecticidal soap solution
- Use a biological control such as Phytoseiulus persimilis
Courgette, sum. squash