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Spider mites
Tetranychus urticae
PestMedium impact
Tiny mites (barely visible to the naked eye) that feed on the underside of leaves, causing pale stippling and fine webbing. Thrive in hot, dry conditions and reproduce extremely rapidly - populations can explode in a polytunnel or glasshouse during a heat wave.
Currently in peak season - extra vigilance worthwhile.
Key facts
- Type
- Pest
- Active season
- Jun - Sep
- Peak season
- Jul - Aug
- Vulnerable stages
- Growing · Harvesting
- Spread rate
- fast
- If confirmed
- Act soon
Signs & symptoms
- -pale yellow or silver speckling across the upper surface of leaves
- -fine, dusty webbing on leaf undersides and around growing tips
- -leaves taking on a dry, bronzed, or washed-out appearance
- -tiny moving dots visible on leaf undersides with a hand lens
Management
Do now
- -Mist foliage to raise humidity - spider mites struggle in humid conditions
- -Remove heavily webbed growth and bin
- -Introduce biological control (Phytoseiulus persimilis) in glasshouse situations
Prevention
- -Maintain adequate humidity in growing areas, especially in polytunnels during hot spells
- -Water plants well during dry periods - drought-stressed plants are far more susceptible
- -Avoid dusty conditions which encourage mite activity
Further reading
- -Spider mites thrive in hot, dry conditions - raising humidity is the single most effective cultural control and can stop an infestation from worsening
- -Populations can double in a week under warm conditions, so early action matters