How to treat a greenhouse for spider mites in autumn after harvest? - briefly
Clean the greenhouse thoroughly, apply an oil‑based miticide or sulfur spray, release predatory mites such as Phytoseiulus persimilis, and maintain low humidity and cooler temperatures to suppress further infestations.
How to treat a greenhouse for spider mites in autumn after harvest? - in detail
Effective control of spider mites in a greenhouse during the autumn period after the crop has been harvested requires an integrated approach that combines sanitation, environmental manipulation, biological agents, and, when necessary, selective chemicals.
Sanitation and removal of residual plant material eliminate preferred habitats for mites. All harvested produce, wilted leaves, and debris should be cleared promptly. Surfaces such as benches, trays, and walkways must be disinfected with a solution of 0.5 % sodium hypochlorite or a commercial greenhouse sanitizer. After cleaning, allow the structure to dry completely before re‑entering.
Environmental adjustments reduce mite reproduction. Maintain daytime temperatures between 18 °C and 22 °C; lower temperatures below 15 °C suppress egg laying. Reduce relative humidity to 50 %–60 % by increasing ventilation and using dehumidifiers. Ensure continuous airflow to prevent stagnant microclimates where mites thrive.
Biological control agents provide long‑term suppression. Release predatory mites (e.g., Phytoseiulus persimilis, Neoseiulus californicus) at a rate of 1 – 2 predators per square meter. Apply the predators in the early evening to protect them from direct sunlight. Supplement with entomopathogenic fungi such as Beauveria bassiana, applied as a foliar spray at the manufacturer‑recommended concentration.
Chemical interventions should follow a rotation schedule to avoid resistance. Use acaricides with different modes of action, for example:
- Abamectin – contact and ingestion, applied at 0.5 ml L⁻¹, repeat after seven days if monitoring shows resurgence.
- Spiromesifen – systemic, applied at 0.2 ml L⁻¹, effective against all mobile stages.
- Sulfur dust – contact, applied at 1 g m⁻², safe for most crops and compatible with predatory mites.
Before each application, inspect plants with a 10× hand lens to assess mite density. Treat only when the population exceeds the economic threshold of five mobile mites per leaf.
Monitoring continues throughout the season. Place sticky traps on the upper and lower tiers of the greenhouse, replace them weekly, and count captured mites. Record data in a logbook to identify population trends and evaluate control efficacy.
Finally, prepare the greenhouse for the next planting cycle. After pest management, perform a thorough fumigation with a vapor‑phase disinfectant such as hydrogen peroxide vapor, ensuring all surfaces are free of viable mites and eggs. Seal the structure for 24 hours to allow complete penetration of the fumigant. Once cleared, install new crop supports and resume cultivation.