What to use to treat cucumbers in a greenhouse against spider mites during fruiting in polycarbonate? - briefly
Use horticultural oil (neem or mineral oil) or a registered acaricide such as abamectin, spinosad, or sulfur, applied at label‑recommended rates with thorough coverage of leaf undersides.
What to use to treat cucumbers in a greenhouse against spider mites during fruiting in polycarbonate? - in detail
Cucumber production in polycarbonate‑covered greenhouses faces severe spider‑mite pressure during the fruiting phase. Effective control requires a combination of chemical, biological, and cultural tactics tailored to the protected environment and the market‑ready stage of the crop.
Chemical options must meet fruit‑safety standards and respect pre‑harvest intervals. Contact miticides such as bifenthrin (0.05 mg L⁻¹) and spirodiclofen (0.1 mg L⁻¹) provide rapid knock‑down but risk resistance if used repeatedly. Systemic products like abamectin (0.015 mg L⁻¹) penetrate plant tissue, protecting developing fruit while maintaining low residue levels. Both classes should be alternated according to label‑specified rotation periods to preserve efficacy.
Biological agents complement chemicals and reduce resistance pressure. Predatory mites—Phytoseiulus persimilis and Neoseiulus californicus—establish quickly on foliage, suppressing populations when released at a rate of 30 predators cm⁻². Entomopathogenic fungi such as Beauveria bassiana (1 × 10⁹ conidia L⁻¹) can be applied as a foliar spray, delivering mortality under humid conditions. Successful deployment requires maintaining relative humidity above 70 % for 24 h post‑application.
Cultural practices limit mite colonisation and enhance treatment performance. Frequent fine‑mist irrigation (2 min every 2 h) reduces leaf temperature and increases humidity, creating an unfavorable environment for mites. Installing reflective mulch beneath the polycarbonate lowers leaf temperature by 2–3 °C, discouraging reproduction. Regular scouting with leaf‑beat trays identifies infestations before economic damage, allowing timely intervention.
An integrated pest‑management (IPM) programme coordinates these measures. Thresholds of 5 mites per leaf trigger the first control action, typically a predatory‑mite release. If populations exceed 10 mites per leaf, a miticide rotation follows, respecting label‑specified PHI. Subsequent cultural adjustments—enhanced ventilation, adjusted irrigation schedules—maintain conditions that deter mite resurgence. Continuous monitoring ensures that each tactic operates within its optimal window, protecting fruit quality while minimizing pesticide input.