How to treat a greenhouse for spider mites in spring and autumn? - briefly
Inspect plants weekly, discard heavily infested foliage, and apply a registered miticide such as neem oil or sulfur‑based spray according to label directions. Follow with a dusting of horticultural oil or release of predatory mites, and keep humidity low with adequate ventilation to prevent re‑infestation.
How to treat a greenhouse for spider mites in spring and autumn? - in detail
Effective control of Tetranychus urticae in a greenhouse during the transitional seasons requires a systematic approach that combines monitoring, cultural adjustments, biological agents, and, when necessary, targeted chemicals.
Begin each season with a thorough inspection. Use a white‑paper tray placed beneath foliage for 10‑15 minutes; the number of motile mites per tray provides a baseline population density. Record findings and repeat the check weekly.
Cultural practices
- Reduce relative humidity to 50‑60 % by increasing ventilation and using dehumidifiers; low humidity limits mite reproduction.
- Maintain temperature between 18‑24 °C; avoid prolonged periods above 28 °C, which accelerate development.
- Remove plant debris and weeds that can harbor overwintering individuals.
- Rotate crops or interplant with non‑host species to disrupt the mite life cycle.
- Prune heavily infested leaves promptly, discarding them away from the greenhouse.
Biological control
- Release predatory phytoseiid mites (e.g., Phytoseiulus persimilis, Neoseiulus californicus) at a rate of 1 predator per 5 cm² of leaf surface when mite counts exceed 5 mites per leaf.
- Apply entomopathogenic fungi such as Beauveria bassiana in a water‑soluble formulation; spray until runoff to ensure coverage of the underside of leaves.
- Introduce predatory insects like Amblyseius swirskii for supplemental suppression, especially on flowering crops.
Chemical intervention (reserved for severe outbreaks)
- Use miticides with low resistance risk, such as abamectin or spirodiclofen, following label‑specified pre‑harvest intervals.
- Rotate active ingredients every 7‑10 days to prevent resistance buildup.
- Apply the product as a fine mist, ensuring thorough wetting of leaf undersides; avoid excess runoff that could damage roots.
Sanitation and equipment
- Clean pots, trays, and benches with a 5 % soap solution before re‑use.
- Disinfect tools with 70 % ethanol after handling infested plants.
- Install sticky traps on frames to monitor adult mite movement and assess control efficacy.
Record‑keeping
- Log temperature, humidity, mite counts, releases of predators, and any pesticide applications.
- Review data after each season to refine thresholds and improve future management plans.
By integrating these measures, growers can keep spider mite populations below economic injury levels throughout both spring and autumn, preserving plant health and yield without reliance on frequent chemical treatments.