How to treat spider mites on cucumbers in a polycarbonate greenhouse? - briefly
Apply a greenhouse‑approved miticide such as sulfur or neem oil and release predatory mites (e.g., Phytoseiulus persimilis) to reduce infestations. Keep leaf surfaces humid (≥ 60 % RH), regularly prune heavily infested vines, and monitor plants to prevent recurrence.
How to treat spider mites on cucumbers in a polycarbonate greenhouse? - in detail
Spider mites thrive in the warm, humid microclimate created by polycarbonate glazing. Effective control requires a combination of preventative measures, regular scouting, and targeted interventions.
First, maintain optimal greenhouse conditions. Keep temperature below 30 °C during the hottest part of the day and ensure good air circulation with fans or vent openings. Reduce leaf wetness by watering at the base of the plants rather than overhead, limiting the moisture film that can encourage mite reproduction.
Second, inspect plants frequently. Examine the undersides of leaves for the characteristic fine webbing and tiny, moving specks. A magnifying lens at 10× magnification is sufficient to confirm presence. Record infestation levels on a simple scale (e.g., 0 = none, 1 = light, 2 = moderate, 3 = severe) to guide treatment decisions.
Third, adopt cultural tactics. Remove heavily infested leaves and discard them away from the greenhouse. Rotate cucumber varieties that exhibit greater resistance to mite damage. Introduce reflective mulches or white screens to increase light intensity, which discourages mite colonization.
Fourth, employ biological agents. Release predatory mites such as Phytoseiulus persimilis or Neoseiulus californicus at a rate of 10–20 predators per square meter. Ensure the greenhouse environment remains within the predator’s temperature tolerance (20–28 °C) and avoid broad‑spectrum insecticides that could harm them. Supplemental food (e.g., pollen) can sustain predator populations during low prey periods.
Fifth, apply horticultural oils or soaps when mite numbers exceed a moderate threshold. Use a neem‑based oil or a potassium salts‑based soap at the label‑recommended concentration, applying to both leaf surfaces until runoff. Repeat applications every 5–7 days until the population declines, and avoid treatment during the hottest part of the day to prevent phytotoxicity.
Sixth, reserve chemical acaricides for severe outbreaks that do not respond to the above measures. Choose products with a short residual activity and low toxicity to humans and beneficial organisms, such as abamectin or spirodiclofen, and rotate modes of action according to the resistance management guidelines. Follow label instructions for dosage, pre‑harvest interval, and personal protective equipment.
Finally, document all actions. Keep a log of scouting dates, infestation scores, biological releases, and any chemical applications. Review the data weekly to adjust the integrated program, ensuring sustainable control while preserving cucumber yield and quality.