How to kill spider mites in a greenhouse? - briefly
Apply a miticide such as abamectin, neem oil, or a sulfur‑based spray, covering all leaf surfaces and maintaining humidity above 60 % to disrupt the mite life cycle. Reinforce control with frequent water misting, removal of heavily infested leaves, and release of predatory insects like Phytoseiulus persimilis.
How to kill spider mites in a greenhouse? - in detail
Spider mites thrive in warm, humid greenhouse conditions, feeding on the undersides of leaves and causing stippling, yellowing, and reduced photosynthesis. Effective eradication requires an integrated approach that combines preventive measures, cultural practices, biological agents, and, when necessary, chemical controls.
First, reduce the environment that favors mite reproduction. Maintain temperature below 80 °F (27 °C) during the hottest part of the day and keep relative humidity above 60 % to disrupt the mite life cycle. Provide adequate ventilation and avoid excessive nitrogen fertilization, which creates tender foliage that attracts the pests.
Second, implement regular scouting. Inspect plant foliage weekly with a 10× hand lens, focusing on leaf undersides. Record infestation levels and map heavily affected zones to target treatments precisely.
Third, apply cultural tactics. Remove and destroy heavily infested leaves or whole plants. Prune overcrowded canopies to improve air flow. Flush the greenhouse with a fine water spray to dislodge mites from leaf surfaces; repeat every 2–3 days while populations are low.
Fourth, introduce biological control agents. Predatory mites such as Phytoseiulus persimilis, Neoseiulus californicus, and Amblyseius swirskii consume all mobile stages of spider mites. Release rates of 50–100 predatory mites per square meter, followed by a weekly supplement during peak infestations, sustain pressure on the pest. Ensure that pesticide applications do not harm these beneficial organisms.
Fifth, consider botanical oils and soaps. Neem oil (5 % active ingredient) and horticultural oil (1–2 % concentration) applied to both leaf surfaces create a suffocating film that kills mites on contact. Use a calibrated sprayer to achieve thorough coverage; repeat every 5–7 days until the population falls below economic threshold.
Sixth, resort to synthetic acaricides only when other measures fail. Select products with short residual activity, such as abamectin or spirotetramat, and rotate modes of action to prevent resistance. Follow label rates precisely, observe pre‑harvest intervals, and protect pollinators and workers with appropriate PPE.
Finally, document all interventions, monitor mite counts after each action, and adjust the program based on observed efficacy. Continuous integration of these steps maintains spider mite populations at manageable levels and safeguards greenhouse productivity.