How should a greenhouse be treated in autumn after a spider‑mite infestation? - briefly
«Remove all visible mites, disinfect all surfaces, and apply a suitable miticide or release predatory mites such as Phytoseiulus persimilis». «Increase ventilation, lower humidity, and cover plants with frost cloth or mulch to prevent re‑infestation during the cooler months».
How should a greenhouse be treated in autumn after a spider‑mite infestation? - in detail
Autumn management of a greenhouse previously affected by spider‑mite colonies requires a systematic approach that eliminates residual populations, restores favorable microclimate conditions, and prevents re‑infestation.
A thorough sanitation cycle should be completed before planting resumes. All plant residues, fallen leaves, and soil surface debris must be removed. Surfaces such as benches, frames, and trays should be scrubbed with a detergent solution and then treated with a disinfectant containing quaternary ammonium compounds or a 10 % bleach solution, allowing a contact time of at least 15 minutes. After drying, the greenhouse interior should be inspected for hidden mite shelters, and any detected refuges must be eliminated.
Biological control agents provide long‑term suppression. Release predatory mites (e.g., Phytoseiulus persimilis or Neoseiulus californicus) at a rate of 10–15 predators per square meter, distributing them evenly across the growing area. Maintain humidity above 60 % and temperature between 20 °C and 25 °C to promote predator activity. Supplemental releases may be necessary if mite counts exceed threshold levels of 5 mites per leaf.
Chemical options remain useful when biological measures alone are insufficient. Select miticides with distinct modes of action, such as bifenazate, abamectin, or spiromesifen, and rotate them according to the Insecticide Resistance Action Committee (IRAC) classification. Apply the product at the label‑specified rate, targeting the undersides of leaves where mites congregate. Conduct treatments early in the day to allow photodegradation of residues before nightfall.
Environmental adjustments reduce the suitability of the greenhouse for mite development. Increase relative humidity by misting or using humidifiers, aiming for 70 % during the night period. Reduce temperature fluctuations by sealing gaps and employing thermal curtains. Enhance ventilation to lower leaf temperature and discourage mite reproduction.
Continuous monitoring validates the effectiveness of interventions. Deploy sticky traps or leaf brush sampling weekly, counting mites under a stereomicroscope. Record population data, treatment dates, and environmental parameters in a logbook to identify trends and refine future protocols.
By integrating sanitation, biological agents, judicious chemical use, and precise environmental control, the greenhouse can be restored to a pest‑free state before the next cropping cycle.