How can I defeat spider mites in a greenhouse? - briefly
Use cultural practices, biological control agents, and selective miticides to eliminate spider mites in greenhouse crops. Maintain low humidity, rinse foliage regularly, and release predatory mites such as Phytoseiulus persimilis for ongoing suppression.
How can I defeat spider mites in a greenhouse? - in detail
Effective control of spider mites in greenhouse production requires an integrated approach that combines cultural, biological, and chemical measures.
First, maintain optimal environmental conditions. Spider mites thrive at temperatures above 25 °C and low humidity. Reducing temperature to 20–22 °C and raising relative humidity to 60–70 % suppresses reproduction rates. Ensure adequate ventilation to prevent hot, stagnant air pockets.
Second, implement strict sanitation. Remove plant debris, fallen leaves, and weeds that can harbor mite colonies. Clean pots, benches, and trellises with a mild detergent solution between crops. Quarantine new plants for at least two weeks and inspect them under a magnifying lens before introduction.
Third, use biological agents. Predatory mites such as Phytoseiulus persimilis, Neoseiulus californicus, and Amblyseius swirskii are effective when released at a ratio of 3–5 predators per adult spider mite. Apply them when mite populations reach 2–3 per leaf, and provide a pollen or yeast supplement to sustain predator numbers.
Fourth, apply horticultural oils and soaps. Neem oil, horticultural oil, and potassium salts (e.g., insecticidal soap) penetrate the mite’s waxy cuticle, causing desiccation. Spray until runoff, covering the undersides of leaves where eggs and motiles reside. Repeat applications every 5–7 days, monitoring for phytotoxicity.
Fifth, resort to selective acaricides only when thresholds are exceeded (e.g., >10 mites per leaf). Choose products with low residual activity and rotate active ingredients to avoid resistance. Examples include abamectin, bifenazate, and spiromesifen. Follow label rates precisely and observe pre‑harvest intervals.
Sixth, monitor continuously. Use sticky traps and leaf beat sampling to estimate population density. Record data weekly to detect early infestations and evaluate the efficacy of each control tactic.
By combining environmental management, sanitation, biological control, safe chemicals, and diligent scouting, greenhouse operators can keep spider mite populations below damaging levels while minimizing chemical inputs and resistance development.