How to treat the soil after a spider mite infestation in a greenhouse? - briefly
Replace the infested top layer of substrate and sterilize the remaining soil by heat (e.g., 45–50 °C for several days) or an approved soil fumigant, then apply a biological control such as predatory mites or beneficial microbes to suppress any residual spider mite populations.
How to treat the soil after a spider mite infestation in a greenhouse? - in detail
After a spider‑mite outbreak, the growing medium often contains mite eggs, webbing, and microbial imbalances that can trigger reinfestation. Effective soil management eliminates residual pests, restores a healthy microbial community, and reduces the risk of recurrence.
- Remove all plant material, fallen leaves, and debris from the beds. Dispose of the material in sealed bags or burn it to prevent egg survival.
- Loosen the soil to a depth of at least 10 cm. This exposes hidden eggs and improves aeration.
- Apply a soil‑sterilization method:
- Thermal: Heat the substrate to 60–70 °C for 30 minutes using a steam‑sterilizer or hot water bath.
- Solar: Spread the soil in thin layers on clear plastic and expose it to direct sunlight for 5–7 days, covering at night to retain heat.
- Chemical: Use a non‑systemic fumigant such as methyl bromide or a suitable soil disinfectant, following label rates and safety guidelines.
- Re‑introduce beneficial microorganisms: incorporate a high‑quality compost, mycorrhizal inoculant, or a commercial microbial blend to outcompete opportunistic pathogens.
- Adjust soil moisture to optimal levels (40–60 % field capacity). Over‑wet conditions favor mold growth, while excessive dryness stresses plants and may encourage mite migration.
- Apply a biological control agent if live mites remain: predatory mites (e.g., Phytoseiulus persimilis) can be released onto the soil surface, where they consume remaining stages.
Monitor the substrate weekly for signs of mite activity or fungal growth. If recurrence is detected, repeat the sterilization cycle and reinforce biological controls. Maintain sanitation, avoid excessive nitrogen fertilization, and ensure proper ventilation to keep the greenhouse environment unfavorable for spider mites.