How can I eradicate spider mites in a greenhouse? - briefly
Apply a registered miticide (e.g., abamectin, neem oil) and release predatory mites such as Phytoseiulus persimilis for biological control. Keep humidity low, rinse plants with water regularly, and quarantine any infested material to stop further infestation.
How can I eradicate spider mites in a greenhouse? - in detail
Effective control of spider mites in a greenhouse requires an integrated approach that combines sanitation, environmental manipulation, biological agents, and targeted chemicals.
Sanitation and cultural practices reduce population buildup. Remove heavily infested leaves and discard them outside the structure. Replace or repair damaged netting that allows mite entry. Rotate crops when possible, and avoid planting host plants consecutively. Keep plant spacing adequate to improve air circulation and reduce leaf humidity, conditions that favor mite reproduction.
Environmental adjustments suppress mite development. Maintain temperatures below 25 °C (77 °F) during peak infestation periods; many mite species reproduce fastest at 28–30 °C (82–86 °F). Lower relative humidity to 50 % or less, as high humidity interferes with mite egg viability. Use exhaust fans and dehumidifiers to achieve these targets.
Biological control introduces natural predators that consume mites rapidly. Common agents include:
- Phytoseiulus persimilis – specializes in spider mite predation, effective at low to moderate infestations.
- Neoseiulus californicus – tolerant of higher temperatures, useful when conditions exceed the optimal range for P. persimilis.
- Amblyseius swirskii – attacks both spider mites and whiteflies, suitable for mixed pest situations.
Release predators at a ratio of 5–10 adult mites per square meter, and re‑apply if mite numbers rise. Provide a pollen source (e.g., Typha pollen) to sustain predator populations when prey density declines.
Chemical options serve as a last resort or for rapid knock‑down. Select products with low residual activity to protect beneficial insects. Effective classes include:
- Abamectin – systemic, disrupts mite nerve function; apply at label‑recommended rate, repeat after 7 days if needed.
- Bifenthrin – contact pyrethroid; use with caution, as it can harm released predators.
- Neem oil – botanical insecticide that interferes with mite feeding; apply early in the morning or late afternoon to avoid photodegradation.
When applying chemicals, rotate active ingredients to prevent resistance development. Follow a strict re‑entry interval and observe pre‑harvest limits.
Monitoring determines the timing of interventions. Inspect the underside of leaves weekly with a 10× hand lens. Count mites per leaf segment; thresholds of 5–10 mites per leaf indicate the need for action. Use sticky traps to detect adult movement and assess predator presence.
Combining these tactics—cleaning, climate control, predator release, judicious chemical use, and regular scouting—provides a reliable framework for eliminating spider mite infestations in greenhouse production.