How to get rid of spider mites in a greenhouse? - briefly
Apply cultural measures (reduce humidity, increase ventilation, and wash foliage with a strong jet of water), introduce predatory mites such as Phytoseiulus persimilis, and, if needed, use a selective acaricide following label instructions. Regular scouting and prompt treatment of new infestations prevent recurrence.
How to get rid of spider mites in a greenhouse? - in detail
Spider mite infestations develop rapidly in greenhouse environments where temperature, humidity, and plant density favor reproduction. Effective management requires an integrated approach that combines cultural, biological, and chemical tactics.
Maintain optimal environmental conditions. Keep temperature between 70‑75 °F (21‑24 °C) and relative humidity above 60 %. Higher humidity interferes with mite egg laying and reduces adult mobility. Ensure adequate ventilation to prevent stagnant air and to disperse leaf‑surface dust that can conceal mites.
Implement rigorous sanitation. Remove plant debris, fallen leaves, and weeds that serve as reservoirs. Disinfect tools, benches, and trays with a 10 % bleach solution or horticultural disinfectant before reuse. Quarantine new stock for at least two weeks and inspect thoroughly for early signs of infestation.
Monitor populations systematically. Place sticky cards or white‑paper traps near the canopy and inspect weekly. Count mites per leaf segment; action thresholds typically range from 5–10 mites per leaf for tender crops and 10–15 for mature plants. Early detection limits the need for more aggressive interventions.
Deploy biological agents. Introduce predatory mites such as Phytoseiulus persimilis, Neoseiulus californicus, or Amblyseius swirskii at a rate of 50–100 individuals per square meter. Release in multiple batches to sustain pressure. Augment with entomopathogenic fungi (e.g., Beauveria bassiana) applied as a foliar spray according to label instructions.
Apply horticultural oils and soaps. Spray neem oil, horticultural oil, or potassium salts at 0.5–2 % concentration, covering both leaf surfaces and undersides. Repeat applications every 5–7 days until mite counts drop below threshold. Ensure thorough coverage to reach concealed feeding sites.
Use selective acaricides when necessary. Choose products with low toxicity to beneficials, such as bifenthrin‑based formulations or spinosad, and follow resistance‑management guidelines: rotate active ingredients, limit applications to three per season, and observe pre‑harvest intervals. Avoid broad‑spectrum insecticides that eradicate natural enemies.
Rotate crops and select resistant varieties where available. Alternate host plants with non‑susceptible species to interrupt the mite life cycle. Prune heavily infested foliage and discard it in sealed bags to reduce inoculum.
Document all actions. Record dates of introductions, applications, environmental readings, and mite counts. Analyze trends to refine timing and dosage of future controls.
By combining environmental regulation, sanitation, vigilant monitoring, biological augmentation, targeted sprays, and prudent chemical use, greenhouse operators can suppress spider mite populations and protect crop health.