How can soil in a greenhouse be disinfected from spider mites? - briefly
A soil drench of a systemic acaricide such as abamectin or a neem‑oil emulsion will kill spider mites present in the medium. After treatment, heat the soil to at least 50 °C for 30 minutes to ensure complete disinfection.
How can soil in a greenhouse be disinfected from spider mites? - in detail
Spider mites can survive in the substrate of a greenhouse, making soil sanitation essential for healthy crop production. Effective decontamination combines physical, chemical, and biological tactics, each applied with precise timing and dosage.
Physical approaches
- Heat treatment: Raise substrate temperature to 50‑55 °C for 30 minutes. Use a portable heater or steam sterilizer; monitor with a calibrated thermometer to avoid overheating and damaging beneficial microbes.
- Solarization: Spread soil in a thin layer (5‑10 cm) on a clear plastic sheet, seal edges, and expose to full sun for 5‑7 days. Temperatures above 45 °C in the top layer suppress mite eggs and larvae.
- Steam pasteurization: Pass steam at 70 °C through the medium for 10 minutes. This method kills immature stages while preserving most organic matter.
Chemical controls
- Insecticidal soaps: Apply a 2‑3 % solution of potassium salts of fatty acids, ensuring thorough saturation of the substrate. Repeat after 7 days to target newly hatched individuals.
- Neem oil emulsions: Use a 0.5‑1 % concentration, mixed with water and a surfactant. Soil drench delivers active azadirachtin to mites feeding on roots.
- Synthetic acaricides: Employ products containing abamectin, spirodiclofen, or bifenthrin according to label rates. Rotate classes to prevent resistance buildup; limit use to avoid phytotoxicity.
Biological options
- Entomopathogenic fungi: Incorporate spores of Beauveria bassiana or Metarhizium anisopliae at 1 × 10⁸ cfu g⁻¹ of substrate. Maintain moisture above 70 % for optimal infection.
- Predatory mites: Release Phytoseiulus persimilis or Neoseiulus californicus onto the soil surface. Provide a refuge of fine mulch to encourage establishment.
- Beneficial nematodes: Apply Steinernema feltiae at 1 million IJs per square meter; nematodes penetrate mite larvae and suppress populations.
Integrated protocol
- Remove plant debris and old potting mix.
- Apply heat or solarization for a minimum of five days.
- After cooling, inoculate the substrate with a fungal biocontrol agent.
- Perform a soil drench with neem oil or insecticidal soap; repeat after one week.
- Introduce predatory mites and maintain humidity at 60‑70 % to support their activity.
- Monitor mite counts weekly using a soil sampling tray; repeat chemical or biological treatments if thresholds exceed 5 mites per 10 cm².
Preventive measures
- Use sterile, commercially supplied potting media for new crops.
- Rotate crops and avoid reusing the same substrate without treatment.
- Install fine mesh screens on vents to limit mite ingress.
- Maintain leaf surface cleanliness; dust and debris can shelter mobile stages that migrate to the soil.
By combining thermal sanitation, targeted acaricides, and biological antagonists, growers can eradicate spider mite infestations in greenhouse substrates while preserving plant health and minimizing chemical residues.