How to treat a greenhouse in autumn for pests and diseases caused by spider mites? - briefly
Apply a miticide early in the autumn cycle, maintain low humidity, and introduce predatory mites such as Phytoseiulus persimilis for biological control. Seal gaps, remove infested debris, and regularly monitor temperature and plant health to prevent reinfestation.
How to treat a greenhouse in autumn for pests and diseases caused by spider mites? - in detail
Effective autumn management of a greenhouse plagued by spider‑mite infestations and the diseases they transmit requires a systematic approach that combines monitoring, cultural adjustments, biological control, and targeted chemical applications.
Begin by establishing a rigorous scouting routine. Inspect leaves twice weekly, focusing on the undersides where mites congregate. Look for stippling, yellowing, and fine webbing. Record population thresholds; action is warranted when mite numbers exceed 5 mites per leaf square centimeter or when disease symptoms appear on more than 10 % of the foliage.
Adjust environmental parameters to create unfavorable conditions for the pest. Reduce temperature to 15–18 °C during the night and maintain daytime temperatures no higher than 22 °C. Increase relative humidity to 70–80 % by employing misting systems or humidifiers, as dry air accelerates mite reproduction. Ensure adequate ventilation to prevent condensation while maintaining the desired humidity level.
Implement cultural practices that disrupt mite life cycles. Remove and destroy heavily infested plant material promptly. Rotate crops with non‑host species for at least one month before re‑introducing susceptible crops. Clean and disinfect benches, tools, and containers with a 10 % bleach solution to eliminate residual eggs and pathogens.
Introduce biological agents as the primary control measure. Apply predatory mites such as Phytoseiulus persimilis or Neoseiulus californicus at a rate of 50 – 100 predators per square meter, repeating applications every 7–10 days until mite populations decline. Supplement with entomopathogenic fungi (e.g., Beauveria bassiana) applied as a foliar spray at 1 × 10⁸ conidia ml⁻¹, ensuring thorough coverage of leaf undersides.
Reserve chemical interventions for severe outbreaks that do not respond to biological control. Use miticides with low residual activity and minimal impact on beneficial organisms, such as abamectin (0.5 ml l⁻¹) or spirodiclofen (0.2 ml l⁻¹), applied according to label rates and rotated every 14 days to prevent resistance. Follow each application with a thorough rinse of the greenhouse to remove residues that could harm predators.
Monitor disease development closely. For viral or fungal diseases transmitted by mites, employ resistant cultivars where available. Apply systemic fungicides (e.g., fosetyl‑Al 0.2 %) to protect against secondary infections, but limit use to early signs of disease to avoid phytotoxicity.
Maintain a detailed log of all interventions, environmental readings, and pest counts. Review the data weekly to adjust strategies promptly, ensuring that mite populations remain below economic thresholds and disease incidence stays minimal throughout the autumn season.