How and with what to treat a greenhouse in autumn for spider mite control? - briefly
Apply horticultural or neem oil sprays early in the autumn, covering all foliage and repeating every 7–10 days until temperatures drop below 10 °C, and maintain low humidity with good ventilation. If populations remain high, introduce predatory mite species such as Phytoseiulus persimilis for biological control.
How and with what to treat a greenhouse in autumn for spider mite control? - in detail
Treating a greenhouse in the autumn season to suppress spider mite populations requires an integrated approach that combines preventive measures, cultural adjustments, biological agents, and, when necessary, selective chemicals.
First, monitor the crop regularly. Use a white‑paper tray or leaf‑stamping method weekly; a count of more than five motile stages per leaf indicates the need for action.
Sanitation and cultural tactics:
- Remove heavily infested leaves and dispose of them away from the structure.
- Clean benches, pots, and screens with a mild detergent solution to eliminate residual eggs.
- Reduce plant density to improve air circulation and lower leaf temperature, conditions that discourage mite development.
- Adjust heating to maintain daytime temperatures between 18‑20 °C; cooler nights slow reproduction cycles.
Biological control options:
- Release predatory mites (e.g., Phytoseiulus persimilis, Neoseiulus californicus) at a rate of 5–10 predators per m², repeating applications every 5–7 days until pest numbers drop below economic thresholds.
- Apply entomopathogenic fungi such as Beauveria bassiana in a water‑soluble formulation; spray until runoff, covering undersides of leaves where mites reside.
- Ensure compatible environmental conditions (relative humidity 70 % for fungi, 60‑80 % for predatory mites) to maximize efficacy.
Chemical interventions, reserved for severe outbreaks:
- Use acaricides with low residual activity, such as abamectin or spirodiclofen, at label‑recommended rates; rotate modes of action every 10‑14 days to prevent resistance.
- Follow strict pre‑harvest intervals and observe re‑entry intervals to safeguard worker health.
Integration and timing:
- Begin preventive releases of predatory mites early in the season, before temperatures fall below 15 °C.
- Introduce fungal sprays when humidity rises above 70 % during evening hours to enhance infection.
- Apply the first selective acaricide only after confirming that biological agents have failed to reduce populations to acceptable levels.
Record-keeping:
- Log temperature, humidity, mite counts, and treatment dates. Trend analysis helps refine schedules for subsequent autumn cycles.
By maintaining vigilant monitoring, optimizing greenhouse microclimate, deploying natural enemies, and reserving chemicals for confirmed failures, growers can effectively manage spider mite pressures throughout the autumn period.