How can I fight spider mites in greenhouses? - briefly
Apply an integrated pest‑management strategy: monitor crops, introduce predatory mites (e.g., Phytoseiulus persimilis), and treat infestations with horticultural oil or sulfur spray while maintaining low humidity and good ventilation. Combine cultural controls, biological agents, and timely chemical applications to keep spider mite populations below damaging levels.
How can I fight spider mites in greenhouses? - in detail
Effective control of spider mites in greenhouse production requires a systematic approach that combines prevention, monitoring, and targeted interventions.
Accurate monitoring is the first step. Inspect the undersides of leaves weekly using a hand lens or a low‑magnification microscope. Record mite counts and note the progression of infestations. Thresholds vary by crop, but a common action point is 5–10 mites per leaf.
Cultural practices reduce the suitability of the environment for mite development. Maintain temperatures below 25 °C when feasible, because high temperatures accelerate reproduction. Keep relative humidity above 60 % to deter mite colonization; humidification or misting systems can achieve this. Remove plant debris, weeds, and infested material promptly. Rotate crops and avoid planting the same species in the same location for consecutive cycles.
Mechanical measures provide immediate reduction. Use vigorous water sprays to dislodge mites from foliage; repeat every 2–3 days during outbreaks. Install sticky traps of yellow or blue color along aisles to monitor population levels and capture adult mites.
Biological agents form the core of sustainable management. Release predatory mites such as Phytoseiulus persimilis, Neoseiulus californicus, or Amblyseius swirskii at a rate of 5–10 predators per square meter. Ensure that releases occur early, before the pest reaches the action threshold. Supplemental releases may be necessary after pesticide applications. Entomopathogenic fungi like Beauveria bassiana can be applied as a foliar spray; maintain leaf wetness for at least 12 hours to allow infection.
Chemical options are reserved for severe infestations or when biological control is insufficient. Select miticides with distinct modes of action to avoid resistance buildup. Commonly used products include abamectin (chlorinated phenylpropanoid), spirotetramat (tetramic acid), and bifenazate (carboxylic acid). Apply according to label rates, targeting the juvenile stages of the mite. Rotate chemicals every 3–4 applications and incorporate a 7‑day interval between treatments and releases of predatory mites.
Integrated pest management (IPM) ties all components together. Develop a schedule that begins with regular scouting, followed by cultural adjustments, then mechanical removal, and finally biological or chemical interventions as needed. Document each action, mite count, and environmental condition to refine thresholds and improve future responses.
By maintaining optimal climate conditions, eliminating host material, employing predatory organisms, and applying chemicals judiciously, greenhouse operators can suppress spider mite populations while preserving crop health and product quality.