Spider Mite
Predatory mites such as Phytoseiulus.
Spider mites thrive in warm, dry conditions. Phytoseiulus persimilis provides fast suppression...
About Spider Mites
Spider mites, particularly the two-spotted spider mite (Tetranychus urticae), are one of the most damaging pests in protected horticulture. They thrive in warm, dry conditions and multiply rapidly, causing leaf speckling, bronzing and eventually plant collapse if left unmanaged. Even small populations can expand explosively during summer or under glasshouse heating.
Symptoms of Spider Mite Damage
- Fine pale speckling (“stippling”) on upper leaf surfaces
- Bronzing or yellowing of foliage
- Fine webbing between leaves, stems and growing points
- Leaf drop and reduced plant vigour
- Rapid spread in hot, dry weather
Why Biological Control Works
Spider mites are highly susceptible to predatory mites. These beneficial predators actively hunt mites at all life stages and reproduce quickly under the same warm conditions that favour the pest. Key species such as Phytoseiulus persimilis provide rapid knockdown, while Amblyseius swirskii and Amblyseius andersoni offer long-term prevention and early-season protection.
Common UK Spider Mite Species
- Tetranychus urticae — Two-spotted spider mite (most common)
- Tetranychus cinnabarinus — Carmine mite
- Panonychus ulmi — Fruit-tree red spider mite
IPM Recommendations
- Start predators early, especially in warm, dry environments
- Use Phytoseiulus persimilis for curative knockdown
- Use Amblyseius swirskii or A. andersoni for prevention
- Mist lightly or raise humidity to slow mite reproduction
- Monitor leaf undersides weekly with a hand lens
- Avoid broad-spectrum insecticides and sulphur, which harm beneficial mites
Preventative vs Curative Strategy
Preventative: Apply slow-release sachets of Amblyseius swirskii or Amblyseius andersoni early in the season to suppress any incoming mites.
Curative: When hot spots appear, release large numbers of Phytoseiulus persimilis directly onto affected plants for fast suppression.
Environmental Notes
- Phytoseiulus needs 18–30°C and good humidity to thrive
- Amblyseius swirskii is excellent in warm summer crops
- Amblyseius andersoni performs even at cooler temperatures
- Low humidity increases spider mite reproduction — increase RH where possible
Biological Controls for Spider Mite
The options below are examples of beneficial insects and biological products commonly used against spider mite. Always refer to supplier guidance and product labels for crop safety and local registration status.
Phytoseiulus persimilis
Product: Phytoline
Environment: glasshouse
Temperature Range: 15.0 – 32.0°C
Rate: 10-20/m²
Frequency: Weekly until control
Curative
Amblyseius californicus
Product: Californiline
Environment: glasshouse
Temperature Range: 20.0 – 30.0°C
Rate: 25-50m²
Frequency: 14 days
Preventative
Amblyseius andersoni
Product: Anderline
Environment: glasshouse
Temperature Range: 6.0 – 30.0°C
Rate: 25-50m²
Frequency: 14 days
Preventative
Feltiella acarisuga
Product: Feltiline
Environment: glasshouse
Temperature Range: 15.0 – 30.0°C
Rate: 0.5–1/m²
Frequency: Weekly until control
Curative
Phytoseiulus persimilis
Product: Phytoline
Environment: outside
Temperature Range: 15.0 – 32.0°C
Rate: 10-20/m²
Frequency: Weekly until control
Curative
Amblyseius andersoni
Product: Anderline
Environment: outside
Temperature Range: 6.0 – 30.0°C
Rate: 25-50m²
Frequency: 14 days
Preventative
Feltiella acarisuga
Product: Feltiline
Environment: outside
Temperature Range: 15.0 – 30.0°C
Rate: 0.5–1/m²
Frequency: Weekly until control
Curative
Phytoseiulus persimilis
Product: Phytoline
Environment: tunnel
Temperature Range: 15.0 – 32.0°C
Rate: 10-20/m²
Frequency: Weekly until control
Curative
Amblyseius andersoni
Product: Anderline
Environment: tunnel
Temperature Range: 6.0 – 30.0°C
Rate: 25-50m²
Frequency: 14 days
Preventative
Feltiella acarisuga
Product: Feltiline
Environment: tunnel
Temperature Range: 15.0 – 30.0°C
Rate: 0.5–1/m²
Frequency: Weekly until control
Curative
Related Biological Solutions
Growers dealing with spider mite often also monitor these pests as part of a complete IPM programme: