How to treat a polytunnel for spider mites? - briefly
Apply a horticultural oil or neem‑based spray to all plant surfaces and tunnel walls early in the day, repeating the treatment every 7‑10 days until mites disappear. Follow with thorough removal of plant debris and release of predatory mite species to sustain control.
How to treat a polytunnel for spider mites? - in detail
Spider mites thrive in warm, dry environments typical of poly‑tunnel structures. Effective management requires an integrated approach that combines sanitation, cultural practices, biological agents, and, when necessary, selective chemicals.
Begin with regular scouting. Examine leaves every 3–5 days, focusing on the undersides where mites lay eggs and feed. Look for stippling, yellowing, or fine webbing. Record infestation levels to guide treatment thresholds.
Sanitation measures reduce initial populations:
- Remove and destroy heavily infested plants or severely damaged foliage.
- Clean tunnel surfaces, benches, and tools with a dilute bleach solution (1 % sodium hypochlorite) to eliminate residual eggs.
- Avoid excessive ventilation that creates hot, low‑humidity zones; maintain relative humidity above 60 % when possible.
Cultural controls limit mite reproduction:
- Water plants thoroughly to raise humidity; misting systems or bottom‑watering are effective.
- Provide adequate spacing to improve air circulation and reduce leaf temperature.
- Rotate crops annually; avoid planting the same host species consecutively in the same tunnel.
Biological agents offer sustainable suppression:
- Release predatory mites (e.g., Phytoseiulus persimilis or Neoseiulus californicus) at a rate of 10–20 predators per square foot when mite counts exceed 5 mites per leaf.
- Apply entomopathogenic fungi such as Beauveria bassiana according to label instructions; these fungi infect and kill spider mites while sparing beneficial insects.
- Ensure compatible environmental conditions (temperature 20–30 °C, relative humidity 70 %) to maximize predator efficacy.
Chemical options serve as a last resort and must be used judiciously:
- Choose products classified as miticides with low toxicity to non‑target organisms, such as abamectin or spirodiclofen.
- Apply according to the manufacturer’s dosage, targeting the leaf undersides where mites congregate.
- Rotate active ingredients every 7–10 days to prevent resistance development.
- Observe pre‑harvest intervals and residue limits to maintain food safety.
Monitoring continues after treatment. Re‑inspect plants 48 hours post‑application and weekly thereafter. Maintain records of mite counts, control measures applied, and environmental conditions to refine future interventions.
By adhering to this systematic protocol—early detection, rigorous sanitation, humidity management, biological augmentation, and prudent chemical use—spider mite outbreaks can be kept at a manageable level, preserving plant health and product quality within the tunnel environment.