How to disinfect soil in a greenhouse in autumn from spider mites? - briefly
Apply a soil drench of neem oil or a horticultural oil at a concentration of 1 %–2 % before the first frost, then cover the beds with a polyethylene sheet for 7–10 days to maintain humidity and kill the mites. Follow with a thorough irrigation using a calcium carbonate solution (1 kg per 100 L water) to neutralize residual oil and restore soil pH.
How to disinfect soil in a greenhouse in autumn from spider mites? - in detail
Effective soil sanitation in a greenhouse during the autumn season requires a systematic approach to eliminate spider‑mite infestations. The process begins with removal of plant debris, which serves as a reservoir for mite eggs and larvae. All spent media, fallen leaves, and twigs should be collected and incinerated or composted at temperatures above 55 °C to ensure complete destruction of any surviving stages.
The next step involves soil treatment. Two principal methods are recommended:
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Thermal disinfection – Fill the cultivation beds with clean, inert material such as sand or perlite, then apply steam at 80–90 °C for 30 minutes. Steam penetrates the substrate, killing mites at all life stages without leaving chemical residues. After cooling, the inert material can be removed and the original soil returned to the beds.
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Chemical disinfection – Apply a soil drench of a miticide approved for greenhouse use, such as a phosphine‑based product or a neem‑oil emulsion diluted according to the manufacturer’s instructions. Ensure thorough mixing to achieve uniform distribution. Allow the soil to remain moist for the recommended exposure period (typically 24–48 hours) before draining excess solution.
Following treatment, the soil should be aerated. Use a mechanical tiller or a manual fork to loosen the substrate, promoting oxygen flow and preventing the re‑establishment of mite populations. Incorporate a layer of diatomaceous earth or a fine sand mulch (2–3 cm thick) on the surface; this creates a physical barrier that deters mite movement and aids in moisture regulation.
Preventive measures are essential to maintain a mite‑free environment throughout the cooler months:
- Install fine mesh screens on ventilation openings to block mite ingress.
- Regulate temperature and humidity within optimal ranges (18–22 °C, 60–70 % relative humidity) to discourage mite reproduction.
- Implement a regular monitoring schedule, inspecting foliage and soil samples weekly with a hand lens. Early detection enables prompt localized treatment, reducing the need for whole‑soil disinfection.
Finally, before introducing new plants, quarantine them for at least seven days and treat their root zones with a mild miticide solution. This precaution prevents the introduction of external mite populations into the sanitized substrate. By adhering to these steps, greenhouse operators can achieve thorough soil decontamination in autumn, ensuring a healthy growing environment for subsequent crops.